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HvacTech2
 
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Default Thermostat Wiring



Hi David, hope you are having a nice day

On 31-Jul-03 At About 18:56:24, David Martel wrote to All
Subject: Thermostat Wiring

DM 0006315 From: "David Martel"

DM Peter,

DM I think he answered the question. C Black/Blue - Common of 24 VAC
DM transformer G Green - Fan relay

if you do this you may blow your transformer.


-= HvacTech2 =-


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Peter
 
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On Thu, 31 Jul 2003 17:18:34 GMT, "Travis Jordan" wrote:

Peter wrote:
I'd like to find out whether there is any "standard" to the wiring
between home thermostats and the HVAC equipment.

The thermostats in my house are connected to the HVAC units in the
basement via a 5 conductor cable. Yellow, green, white, red, blue.

The blue is not connected. I *assume* that two of the other four are
the main on/off and the other two are for the fan on/auto switch.
Can I tell by color which is which or do I have to open up the
thermostat and look?

Thanks.

Peter


Most installers adopt the commonly used 'standard' wire color code.
Here's a sample of some typical usage:

R Red - Power 24 VAC transformer
C Black/Blue - Common of 24 VAC transformer
W White - Primary heat call relay
E Brown - Emergency heat relay
Y Yellow - Primary cool call relay
G Green - Fan relay
O Orange - Change-over to cool relay
B Blue - Change-over relay to heat relay

Here's as much as you will ever want to know about the various
manufacturer's equipment-to-thermostat connections:

http://hbctechlit.honeywell.com/tech...0s/70-6627.pdf


So, which two wires are for the fan On function. Green is one, which is
the other?

In other words, if I wanted to run a jumper between two of the terminals
to force the fan to be On all the time (as if I put the fan switch in the
On position), which two terminals would it be? I assume one is where the
green wire is connected. Which is the other?

Peter

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jim
 
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Default Thermostat Wiring

Peter wrote:

On Thu, 31 Jul 2003 17:18:34 GMT, "Travis Jordan" wrote:

Peter wrote:
I'd like to find out whether there is any "standard" to the wiring
between home thermostats and the HVAC equipment.

The thermostats in my house are connected to the HVAC units in the
basement via a 5 conductor cable. Yellow, green, white, red, blue.

The blue is not connected. I *assume* that two of the other four are
the main on/off and the other two are for the fan on/auto switch.
Can I tell by color which is which or do I have to open up the
thermostat and look?

Thanks.

Peter


Most installers adopt the commonly used 'standard' wire color code.
Here's a sample of some typical usage:

R Red - Power 24 VAC transformer
C Black/Blue - Common of 24 VAC transformer
W White - Primary heat call relay
E Brown - Emergency heat relay
Y Yellow - Primary cool call relay
G Green - Fan relay
O Orange - Change-over to cool relay
B Blue - Change-over relay to heat relay

Here's as much as you will ever want to know about the various
manufacturer's equipment-to-thermostat connections:

http://hbctechlit.honeywell.com/tech...0s/70-6627.pdf


So, which two wires are for the fan On function. Green is one, which is
the other?

In other words, if I wanted to run a jumper between two of the terminals
to force the fan to be On all the time (as if I put the fan switch in the
On position), which two terminals would it be? I assume one is where the
green wire is connected. Which is the other?

Peter

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dont think you have to run any jumpers.. just put the switch on FAN and
the fan stays on.. AUTO means automatic and the fan will come on when
the compressor comes on.... and will go off when the compressor goes
off.

hope this helps.
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David Martel
 
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Default Thermostat Wiring

Peter,

I think he answered the question.
C Black/Blue - Common of 24 VAC transformer
G Green - Fan relay


Dave M.



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Peter
 
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Default Thermostat Wiring

On Thu, 31 Jul 2003 23:56:24 GMT, "David Martel"
wrote:

Peter,

I think he answered the question.
C Black/Blue - Common of 24 VAC transformer
G Green - Fan relay


Dave M.


I have yellow, green, white, red, blue wires. The blue wire is not
connected to anything. There is no black wire. That leaves yellow,
green, white, red.

One side of the fan relay is the green wire. The other side is ???
(yellow, white or red).

Peter
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  #6   Report Post  
Trevor Lowe
 
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Default Thermostat Wiring

Poor Peter.. I understand exactly what he's asking, but nobody is providing,
in black and white, the answer. I don't know the answer myself, but why
won'tanyone just tell him?? From all the responses to his posting, it seems
everybody has at least some idea what theyr'e talking about, but nobody will
let him in on their "little secret".

Childish.

Here's the question one more time: What two wires and their standard
corresponding colors would one person/one thermostat/one HVAC tech have to
short/connect together/work magic on to make that wonderful fan motor begin
to turn??

The answer must be in this format to be acceptable:

Black and Red.

Replace the above colors with whatever color would satisfy the
aforementioned question. Else, your response is unwelcome. No intro, no
outro, no silly rant about asking specific questions.. Just three words in
the exact format specified above.

"Peter" wrote in message
...
I'd like to find out whether there is any "standard" to the wiring between
home thermostats and the HVAC equipment.

The thermostats in my house are connected to the HVAC units in the
basement via a 5 conductor cable. Yellow, green, white, red, blue.

The blue is not connected. I *assume* that two of the other four are the
main on/off and the other two are for the fan on/auto switch. Can I tell
by color which is which or do I have to open up the thermostat and look?

Thanks.

Peter

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nunya
 
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Default Thermostat Wiring

Peter,

IF and thats a HUGE IF your thermostat is wired correctly/to the acceptable
standard Red to anything turns that portion of the system on.

Example:
Red and Green = Fan
Red and Orange = reversing valve if so equiped, could be eiter heat or cool
depends on the system.
Red and Yellow = 1st stage cooling
Red and White = 1st stage heat

You should be able to look at your thermostats subbase and confirm that it
is wired correctly before jumping anything. You should have:
Red to Rh and Rc (your 24v feed from the transformer)
Green to G (feeds your fan relay)
Yellow to Y1 (feeds your first stage contactor/time delay circuit)
White to W1 (feeds your gas valve/gun/thermodisks etd etc)

If it's NOT wired like that to a subbase call someone, don't mess with it.
In addition, it appears that you don't know what your doing and you should
stop and call a pro, plain and simple. You mess with it your looking at
several hundred and could be upwards of 1000's (depending on the system) to
replace the components you fry. Simple solution.....place a call to a local
company for probably no more than a cnote will get you someone out there for
this and they will make sure it's done right.

-Brian


"Peter" wrote in message
...
On Thu, 31 Jul 2003 23:56:24 GMT, "David Martel"
wrote:

Peter,

I think he answered the question.
C Black/Blue - Common of 24 VAC transformer
G Green - Fan relay


Dave M.


I have yellow, green, white, red, blue wires. The blue wire is not
connected to anything. There is no black wire. That leaves yellow,
green, white, red.

One side of the fan relay is the green wire. The other side is ???
(yellow, white or red).

Peter
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  #8   Report Post  
Travis Jordan
 
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Default Thermostat Wiring

Trevor Lowe wrote:
Here's the question one more time: What two wires and their standard
corresponding colors would one person/one thermostat/one HVAC tech
have to short/connect together/work magic on to make that wonderful
fan motor begin to turn??

The answer must be in this format to be acceptable:

Black and Red.


Assuming standard wiring conventions were followed, the answer is:

Greeen and Red.

Although the original question indicated that we should not ask why he
wants to do this, I think we should point out that any external wiring
to the thermostat should be appropriated fused in order to protect the
HVAC equipment.


  #9   Report Post  
David Martel
 
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Default Thermostat Wiring

Hvac,

I meant to write Red to Green, as Nunya has answered. I must have been
1/2 asleep when I posted.
I don't understand why the transformer would be damaged by connecting
it's common through the relay's coil to ground.

Dave M.


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Peter
 
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On Thu, 01 Aug 2003 05:13:53 , "HvacTech2"
wrote:

Hi Peter, hope you are having a nice day

On 31-Jul-03 At About 12:25:47, Peter wrote to All
Subject: Thermostat Wiring

P From: Peter

P What I actually want to do is put in a second On/Auto switch for the
P fan -in parallel with the existing switch. (Don't ask why.) One
P side of the new switch should be wired to the green wire terminal.
P The other side of the new switch wired to what???

This would probably require a relay unless you would like to run the A/C at
the same time.


It will be wired to a relay which will be controlled by my home automation
system. I'm just trying to double check where in the HVAC system I should
wire the relay to.

Peter
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Peter
 
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Default Thermostat Wiring

Just to clarify to anyone who may care what I am planning to do and why I
asked the original question...

I wanted to know which two wires control the fan On/Auto function. I have
since learned from this thread it's green and red. I *will* open the
thermostat to double check that before I do anything else.

I plan to connect a normally-open relay in parallel with the On/Auto
switch. The relay will be controlled by my home automation system. This
will enable me to turn the fan On/Auto from my automation system. I am
not trying to control the heating/cooling functions of my HVAC; just the
fan On/Auto.

Assuming I pick the correct pair of wires (which I think I can now do even
though I am not a "professional") I don't see how this will damage my HVAC
system. If anyone thinks I'm wrong about that I'd certainly like to hear
what you have to say.

Peter
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meirman
 
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Default Thermostat Wiring

In alt.home.repair on Thu, 31 Jul 2003 21:28:28 -0400 Peter
posted:

On Thu, 31 Jul 2003 23:56:24 GMT, "David Martel"
wrote:

Peter,

I think he answered the question.
C Black/Blue - Common of 24 VAC transformer
G Green - Fan relay


Dave M.


I have yellow, green, white, red, blue wires. The blue wire is not
connected to anything. There is no black wire. That leaves yellow,
green, white, red.


Someone pointed out that standard colors are only used most of the
time. Do you have a thermostat connected now? And it works
correctly?

A voltohmmeter?. Turn off the furnace, then you can write down which
wire is connected to which screw on the thermostat, then disconnect
the wires. With the ohmmeter, you can find which pair of screws (and
which pair of corresponding wires) has zero, or near zero, resistance
between them when you have the fan switch on ON and infinite
resistance between them when you have the fan switch on OFF. On the
thermostat.

Since one is probably green, that will likely speed things up a lot.

Connect the switch in parallel to the thermostat switch, (You might
want to turn on the power and test it, then turn off the power again)
and reconnect the thermostat.

It's wonderful and very useful to ask for help, but no one else is at
your home, no one knows if for some strange reason yours wasn't wired
like others. Even human organs aren't always where they are usually
are.

You can also get in the habit of measuring for suitable voltages
before measureing resistance, and before connecting something new.

One side of the fan relay is the green wire. The other side is ???
(yellow, white or red).

Peter



Meirman

If emailing, please let me know whether
or not you are posting the same letter.

Change domain to erols.com, if necessary.
  #13   Report Post  
Gary Tait
 
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Default Thermostat Wiring

On Thu, 31 Jul 2003 21:25:47 -0400, Peter
wrote:

On Thu, 31 Jul 2003 18:07:44 -0500, jim wrote:

Peter wrote:

On Thu, 31 Jul 2003 17:18:34 GMT, "Travis Jordan" wrote:

Peter wrote:
I'd like to find out whether there is any "standard" to the wiring
between home thermostats and the HVAC equipment.

The thermostats in my house are connected to the HVAC units in the
basement via a 5 conductor cable. Yellow, green, white, red, blue.

The blue is not connected. I *assume* that two of the other four are
the main on/off and the other two are for the fan on/auto switch.
Can I tell by color which is which or do I have to open up the
thermostat and look?

Thanks.

Peter

Most installers adopt the commonly used 'standard' wire color code.
Here's a sample of some typical usage:

R Red - Power 24 VAC transformer
C Black/Blue - Common of 24 VAC transformer
W White - Primary heat call relay
E Brown - Emergency heat relay
Y Yellow - Primary cool call relay
G Green - Fan relay
O Orange - Change-over to cool relay
B Blue - Change-over relay to heat relay

Here's as much as you will ever want to know about the various
manufacturer's equipment-to-thermostat connections:

http://hbctechlit.honeywell.com/tech...0s/70-6627.pdf

So, which two wires are for the fan On function. Green is one, which is
the other?

In other words, if I wanted to run a jumper between two of the terminals
to force the fan to be On all the time (as if I put the fan switch in the
On position), which two terminals would it be? I assume one is where the
green wire is connected. Which is the other?

Peter

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dont think you have to run any jumpers.. just put the switch on FAN and
the fan stays on.. AUTO means automatic and the fan will come on when
the compressor comes on.... and will go off when the compressor goes
off.

hope this helps.


What I actually want to do is put in a second On/Auto switch for the fan -
in parallel with the existing switch. (Don't ask why.) One side of the
new switch should be wired to the green wire terminal. The other side of
the new switch wired to what???

Peter


This has reached the poin where you might want to take a look at the
furnace and see what wires go where at that end.
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HvacTech2
 
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Default Thermostat Wiring



Hi Travis, hope you are having a nice day

On 01-Aug-03 At About 07:44:17, Travis Jordan wrote to All
Subject: Thermostat Wiring

TJ From: "Travis Jordan"

TJ Trevor Lowe wrote:
Here's the question one more time: What two wires and their standard
corresponding colors would one person/one thermostat/one HVAC tech
have to short/connect together/work magic on to make that wonderful
fan motor begin to turn??


The answer must be in this format to be acceptable:


Black and Red.


TJ Assuming standard wiring conventions were followed, the answer is:

TJ Greeen and Red.

TJ Although the original question indicated that we should not ask why
TJ he wants to do this, I think we should point out that any external
TJ wiring to the thermostat should be appropriated fused in order to
TJ protect the HVAC equipment.

There is a lot more to it than this. the G is connected to the Y internally on
most thermostats. and jumpering these out will cause the A/C to run which
will damage the compressor.


-= HvacTech2 =-


... URA Redneck if you think cow tipping should be an Olympic sport.

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HvacTech2
 
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Default Thermostat Wiring



Hi 'nuther, hope you are having a nice day

On 01-Aug-03 At About 09:01:39, 'nuther Bob wrote to All
Subject: Thermostat Wiring

'B From: 'nuther Bob

'B On Thu, 01 Aug 2003 05:16:08 , "HvacTech2"
'B wrote:

'B If only it were that simple, but of course it isn't. by doing
'B what he wants to do the A/C would run at the same time which could
'B easily damage his compressor. and no, I do not give answers so
'B someone can damage their system.

'B Yeah, but he posted this in a followup:

'B "What I actually want to do is put in a second On/Auto switch for the
'B fan - in parallel with the existing switch. (Don't ask why.) One
'B side of the new switch should be wired to the green wire terminal.
'B The other side of the new switch wired to what???"

'B So, he's got a fan switch already. All he has to do is mimic that
'B switch.

Sorry you are wrong. I of course cannot see what he has but most thermostats
use a Y to G internal connection inside to run the fan when the A/C comes on.
if you parallel that, whenever you run the new switch you will run the A/C
and damage it.




-= HvacTech2 =-


... "Curiosity killed the cat, but for a while I was a suspect."- s.w.

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HvacTech2
 
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Hi Peter, hope you are having a nice day

On 01-Aug-03 At About 01:12:17, Peter wrote to All
Subject: Thermostat Wiring

P From: Peter

P Just to clarify to anyone who may care what I am planning to do and
P why I asked the original question...

P I wanted to know which two wires control the fan On/Auto function. I
P have since learned from this thread it's green and red. I *will*
P open the thermostat to double check that before I do anything else.

P I plan to connect a normally-open relay in parallel with the On/Auto
P switch. The relay will be controlled by my home automation system.
P This will enable me to turn the fan On/Auto from my automation
P system. I am not trying to control the heating/cooling functions
P of my HVAC; just the fan On/Auto.

P Assuming I pick the correct pair of wires (which I think I can now do
P even though I am not a "professional") I don't see how this will
P damage my HVAC system. If anyone thinks I'm wrong about that I'd
P certainly like to hear what you have to say.

what is the model number of your thermostat? if it is a honeywell T87?? or
one of several other mechanical models this will cause the A/C to run and it
will cause damage. the relay may have to be wired differently to make it
work.


-= HvacTech2 =-


... And now, a brief musical interlude

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  #17   Report Post  
Travis Jordan
 
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Default Thermostat Wiring

HvacTech2 wrote:
Hi Travis, hope you are having a nice day

On 01-Aug-03 At About 07:44:17, Travis Jordan wrote to All
Subject: Thermostat Wiring

From: "Travis Jordan"


Trevor Lowe wrote:
Here's the question one more time: What two wires and their

standard corresponding colors would one person/one thermostat/one
HVAC tech have to short/connect together/work magic on to make
that wonderful fan motor begin to turn??

The answer must be in this format to be acceptable:


Black and Red.


Assuming standard wiring conventions were followed, the answer is:


Greeen and Red.


Although the original question indicated that we should not ask why
he wants to do this, I think we should point out that any external
wiring to the thermostat should be appropriated fused in order to
protect the HVAC equipment.


There is a lot more to it than this. the G is connected to the Y
internally on most thermostats. and jumpering these out will cause
the A/C to run which will damage the compressor.

-= HvacTech2 =-


The poster indicated that his thermostat has the 'fan on' only feature.

Also, remember that his original post said:

"The thermostats in my house are connected to the HVAC units in the
basement via a 5 conductor cable. Yellow, green, white, red, blue."

We're assuming that the appearance of a (G) - fan relay wire means that
it is functional, and also that he is smart enough to know that the
current configuration does work to allow him to run the fan only (after
all, that is what he is planning on doing with his new control system).

Besides, even if G and Y were connected together, so what? If his
external control system were to attempt to short-cycle the compressor,
I would hope most modern compressors would have time delays built in.
After all, there is always the momentary power outage for the HVAC
manufacturer to worry about.


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HvacTech2
 
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Hi Peter, hope you are having a nice day

On 01-Aug-03 At About 10:55:28, Peter wrote to All
Subject: Thermostat Wiring

P From: Peter

P On Thu, 01 Aug 2003 19:22:39 , "HvacTech2"
P wrote:

P 1. Is there any way to do this without damaging my HVAC system?

P 2. If so, to what terminals on the control panel inside my HVAC unit
P should I connect the relay?
P it isn't that simple. you will need a single pole double throw
P relay and a special hookup to do what you want.

P You've convinced me that it's not as simple as just connecting my
P external relay to the green & red wires. Just so I understand this
P better, can you explain why that is. What "bad things" would happen
P if I did that?

What would happen is you would run the A/C compressor every time that relay
kicked in for the fan. there is an internal connection in the thermostat
between Y and G when the fan is in auto position. if you left it in the on
position it would be OK but that would defeat the purpose of the relay

-= HvacTech2 =-


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  #19   Report Post  
Peter
 
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On Thu, 01 Aug 2003 17:08:19 , "HvacTech2"
wrote:

what is the model number of your thermostat? if it is a honeywell T87?? or
one of several other mechanical models this will cause the A/C to run and it
will cause damage. the relay may have to be wired differently to make it
work.


I'm out of town now so I can't tell you the model number of my thermostat
but I will post that here when I'm back home next week. For now I can
tell you that it is a non-programmable mechanical model. Honeywell, I
think but I'm not positive.

Perhaps I should rephrase my original question to the following:

I want to connect an external normally-open relay to my HVAC system that
will paralel the function of the fan on/auto switch on my thermostat.
When the relay is closed it would be the same as the fan switch being in
the on position and when the relay is open it would be the same as the fan
switch being in the auto position. The relay should control only the fan;
it should not cause the compressor or heating system to run. Those
functions should continue to be controlled only by the thermostat setting.

That being the objective...

1. Is there any way to do this without damaging my HVAC system?

2. If so, to what terminals on the control panel inside my HVAC unit
should I connect the relay?

Peter

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HvacTech2
 
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Hi meirman, hope you are having a nice day

On 02-Aug-03 At About 04:51:53, meirman wrote to All
Subject: Thermostat Wiring

m From: meirman


m I think the terminology here might be a problem. On the thermostats
m I've used, if you turn the fan switch to ON**, the fan runs whether
m the A/C is on or not.


Think of it as a double pole single throw relay. G is common and there is R
and Y, when you are in auto G is connected to Y internally so that when Y (
cooling ) calls the fan runs at the same time. when you switch it to Fan On
it connects to R and disconnects from Y

m The A/C might be enabled***, but unless the
m house is hot enough that the the temperature setting is lower than
m the house temperature at the thermostat, and the compressor is
m running, I don't think most of us would say that the A/C has "come
m on".

See above.


m ***I"m not sure the industry term for this, but I mean by "enabled"
m that the A/C is ready to run as soon as the house is hot enough to
m cause the thermal switch to turn it on. What is the industry term
m for this? **Peter is trying to duplicate the ON setting for the fan
m switch, not the AUTO setting.

See above.

m To us, it's hard to understand when you say it runs the fan when the
m A/C comes on, if it runs the fan all the time.

See above.


m If there is an internal connection from the G to the Y, which is the
m primary cool call relay, what would happen if that internal
m connection was broken and the thermal part of the thermostat was
m relied on to turn on the compressor?

There is no "thermal part" to turn on the fan. again, see above.


m if you parallel that, whenever you run the new switch you will run
m the A/C and damage it.

m Do you mean, because even though the fan and compressor are on,
m eventually the house will be as cold as the A/C can make it, but it
m will keep running? Would that damage it?

Yes it will damage it. anything below abut 68 degrees indoor can cause the
evaporator to freeze which will slug the compressor with liquid refrigerant
and damage it.

m If you mean that would damage it, what happens if I use my current
m thermostat and set my A/C on and my thermostat to 33 degrees, and my
m fan on AUTO or ON?

early death for the compressor.

m Even without modifying the thermostat, how come we don't damage our
m A/C's when we have the A/C-Heat switch set to OFF and the Fan switch
m set to AUTO or ON?

see above.

m Can we damage our A/C just by setting the thermostat to settings we
m don't always use?

I don't know what you mean here but running the A/C anywhere below a 68
degree setpoint will cause excessive wear and early compressor failure.



-= HvacTech2 =-


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  #21   Report Post  
Peter
 
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On Fri, 02 Aug 2003 10:50:27 , "HvacTech2"
wrote:

P OK, I can now see that just connecting an external relay to the red
P and green wires is not the right answer. So, what is the way to do
P what I want to do ... to switch just the fan on/off using an exernal
P relay?

it is a little tricky but it can be done. due to liability I don't think I
should go into it.


-= HvacTech2 =-


Please consider this a public release from any liability you may have
(probably none) for any advice you give me on how to connect an external
relay to my home HVAC system to parallel the function of the fan on/auto
switch in my thermostat. I'm not a lawyer but that should cover you.

Peter

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meirman
 
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Default Thermostat Wiring

In alt.home.repair on Sat, 02 Aug 2003 15:20:40 GMT the_plumber
posted:

Peter wrote:


OK, I can now see that just connecting an external relay to the red and
green wires is not the right answer.
Peter



Whatever you do, DON'T CUT THE RED WIRE!


Why? What will happen if I d
  #23   Report Post  
meirman
 
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Default Thermostat Wiring

In alt.home.repair on Thu, 01 Aug 2003 17:04:11 "HvacTech2"
posted:



Hi 'nuther, hope you are having a nice day

On 01-Aug-03 At About 09:01:39, 'nuther Bob wrote to All
Subject: Thermostat Wiring

'B From: 'nuther Bob

'B On Thu, 01 Aug 2003 05:16:08 , "HvacTech2"
'B wrote:

'B If only it were that simple, but of course it isn't. by doing
'B what he wants to do the A/C would run at the same time which could
'B easily damage his compressor. and no, I do not give answers so
'B someone can damage their system.

'B Yeah, but he posted this in a followup:

'B "What I actually want to do is put in a second On/Auto switch for the
'B fan - in parallel with the existing switch. (Don't ask why.) One
'B side of the new switch should be wired to the green wire terminal.
'B The other side of the new switch wired to what???"

'B So, he's got a fan switch already. All he has to do is mimic that
'B switch.

Sorry you are wrong. I of course cannot see what he has but most thermostats
use a Y to G internal connection inside to run the fan when the A/C comes on.


I think the terminology here might be a problem. On the thermostats
I've used, if you turn the fan switch to ON**, the fan runs whether
the A/C is on or not. The A/C might be enabled***, but unless the
house is hot enough that the the temperature setting is lower than the
house temperature at the thermostat, and the compressor is running, I
don't think most of us would say that the A/C has "come on".

***I"m not sure the industry term for this, but I mean by "enabled"
that the A/C is ready to run as soon as the house is hot enough to
cause the thermal switch to turn it on. What is the industry term for
this? **Peter is trying to duplicate the ON setting for the fan
switch, not the AUTO setting.


To us, it's hard to understand when you say it runs the fan when the
A/C comes on, if it runs the fan all the time.

If there is an internal connection from the G to the Y, which is the
primary cool call relay, what would happen if that internal connection
was broken and the thermal part of the thermostat was relied on to
turn on the compressor? Would not the fan either stay on all the time
if the switch were in the ON position, or go on when it should if in
the Auto position?

if you parallel that, whenever you run the new switch you will run the A/C
and damage it.


Do you mean, because even though the fan and compressor are on,
eventually the house will be as cold as the A/C can make it, but it
will keep running? Would that damage it?

If you mean that would damage it, what happens if I use my current
thermostat and set my A/C on and my thermostat to 33 degrees, and my
fan on AUTO or ON?


Even without modifying the thermostat, how come we don't damage our
A/C's when we have the A/C-Heat switch set to OFF and the Fan switch
set to AUTO or ON?

Or when we have the A/C-Heat switch set to A/C, the thermostat set to
100 degrees (or anything hotter than what the house is), and the Fan
switch set to AUTO or ON?

Can we damage our A/C just by setting the thermostat to settings we
don't always use?

-= HvacTech2 =-


.. "Curiosity killed the cat, but for a while I was a suspect."- s.w.

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  #24   Report Post  
meirman
 
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Default Thermostat Wiring

In alt.home.repair on Sat, 02 Aug 2003 13:51:53 -0400 meirman
posted:

In alt.home.repair on Thu, 01 Aug 2003 17:04:11 "HvacTech2"
posted:



Hi 'nuther, hope you are having a nice day

On 01-Aug-03 At About 09:01:39, 'nuther Bob wrote to All
Subject: Thermostat Wiring

'B From: 'nuther Bob

'B On Thu, 01 Aug 2003 05:16:08 , "HvacTech2"
'B wrote:

'B If only it were that simple, but of course it isn't. by doing
'B what he wants to do the A/C would run at the same time which could
'B easily damage his compressor. and no, I do not give answers so
'B someone can damage their system.

'B Yeah, but he posted this in a followup:

'B "What I actually want to do is put in a second On/Auto switch for the
'B fan - in parallel with the existing switch. (Don't ask why.) One
'B side of the new switch should be wired to the green wire terminal.
'B The other side of the new switch wired to what???"

'B So, he's got a fan switch already. All he has to do is mimic that
'B switch.

Sorry you are wrong. I of course cannot see what he has but most thermostats
use a Y to G internal connection inside to run the fan when the A/C comes on.


I think the terminology here might be a problem. On the thermostats
I've used, if you turn the fan switch to ON**, the fan runs whether
the A/C is on or not. The A/C might be enabled***, but unless the
house is hot enough that the the temperature setting is lower than the
house temperature at the thermostat, and the compressor is running, I
don't think most of us would say that the A/C has "come on".

***I"m not sure the industry term for this, but I mean by "enabled"
that the A/C is ready to run as soon as the house is hot enough to
cause the thermal switch to turn it on. What is the industry term for
this?



**Peter is trying to duplicate the ON setting for the fan
switch, not the AUTO setting.


Replying to my own post, the line above is important, but much of the
rest of my previous post wasn't.

To us, it's hard to understand when you say it runs the fan when the
A/C comes on, if it runs the fan all the time.

If there is an internal connection from the G to the Y, which is the
primary cool call relay, what would happen if that internal connection
was broken and the thermal part of the thermostat was relied on to
turn on the compressor? Would not the fan either stay on all the time
if the switch were in the ON position, or go on when it should if in
the Auto position?

if you parallel that, whenever you run the new switch you will run the A/C
and damage it.


Do you mean, because even though the fan and compressor are on,
eventually the house will be as cold as the A/C can make it, but it
will keep running? Would that damage it?


OK, I still can't guess what Hvac would say to this, but I've figured
out what he is getting at.

If you mean that would damage it, what happens if I use my current
thermostat and set my A/C on and my thermostat to 33 degrees, and my
fan on AUTO or ON?


And I can't figure out what Hvac would say to this, but I can explain
the rest of it.

Hvac is referring to a connection in the thermostat, at least
mechanical ones he seems to say, between the Y (Primary cool call
wire) and the Auto position of the fan switch. He's saying that when
the unit is on A/C and the fan is on AUTO, when the thermostat calls
for cooling and closes the connection from the Red to the Yellow, this
also provides power to the internal connection from the Yellow to the
AUTO position of the fan, and thus runs 24 volts to the Green, so that
the fan goes on.

But, Peter, if you run a the switch part of a relay in simple shunt
with the ON position of the Fan switch, the power will go (logically
only since it is AC current) in the opposite direction, compared to
the last sentence of the previous paragraph**. That is, when the relay
you add sends 24 volts to the Green wire, that 24 volts would be
present at the AUTO lead of the Fan switch. We know the Fan switch is
in the AUTO position, because if it were in the ON position, it would
be ON all the time anyhow and Peter would be asking how to turn it
off, not how to turn it on. When the 24 volts reaches the Fan switch
Auto position, it then goes through the switch to the common terminal
of the Fan switch. And then via the internal connection in the
thermostat, to the Yellow screw/wire, where it goes to the furnace and
activates the cooling relay and cooling function of the AC.

Peter, I think if you stop here for a minute you can figure out what
you need to do, but if you are impatient, meet me after the 7 line
footnote in the next line. Otherwise, pause here to think about it.


**If this were DC, this could be prevented by the use of a diode, but
it is AlternatingCurrent. In some devices, not necessarily Air
Conditioning, one could probably just rectify the whole thing, the
whole power supply, with a diode and then block the current from going
the opposite direction with a well-placed diode in the opposite
direction, but half wave rectification would lower the effective
voltage, require a bunch of testing to make sure everything still
worked, and there is no need for that here.


What to do next?

Use the relay you are controlling remotely to disconnect the Green
lead of the thermostat from the Green lead of the furnace.


In other words, take the Green lead from the furnace-AC and connect it
to the common connector of a double throw relay switch. In the normal
position, have it connected to the Green lead from the thermostat, as
it is now.****

In the activated position, have it connected to the Red lead from the
thermostat/furnace-AC. Of course you don't have to and can't cut the
Red wire.

You can make these connections anywhere along the wire from the
furnace to the thermostat. Probably easiest near the furnace. But
you know that.

Don't forget, if you do a bad job or use a really inferior relay,
that this could lead to the fan not running whether the relay is
activated OR NOT. I guess this is what Hvac is worried about. Don't
forget what you have done, if you ever have problems^^. Don't forget
if you sell the house^^^ to rip out what you've done and solder the
halves of green wire, or tell the next owner what you have done, and
remind him to tell the owner after him.

(I was once involved in a situation where I fiddled with phone lines,
and years after I left, the phone company had to run a whole new wire
from the basement to the second floor, becuase they couldn't figure it
out. I had restored it, but not fully.)

^^I've fiddled with the wires to my stereo, my burglar alasm, my vcr
and its output distribution, and my car until I've made them so
complicated I can't even remember all the wiring. I have to refresh my
memory every time I need to change things. The burglar alarm, at
least I drew myself a schematic. (The car has notes scattered through
the wiring diagram pages in the shop manual)



(Hvac made a reference to needing a double throw relay, but that is
not how I figured this out. It was his reference to the internal
connection. Peter, feel free to sue me if you are foolish enough to
connect this wrong in blind obedience to my directions, without
thinking about it and being convinced on your own that this will work.
How could it not if you do what I say? Anyone else, who has not
released me, may sue me also. )


****As an aside, this setup would be referred to as Fail-Safe. Not
because it is a nuclear weapon where it will destroy the world if we
don't have rigid precautions. But because that compound word means
something specific. It means if your added relay fails, things will
return to normal, the Safe situation. The odds are very very high that
coil in it will de-energize and the relay will go back to its normal
position, and your wires will then be connected the way they were
before you fiddled with them. Of course, since this isn't an
explosive, you might want to reverse those wires so if it fails the
fan will always be on.

^^^I had a beautiful 1930 apartment in Brooklyn NY, with a separate
pipe next to the tub which controlled draining, not draining, and
overflow. In order to get a deeper bathtub, I taped up the overflow
holes, and got about 2 inches more. I was happy for 10 years, never
had an overflow, but I was afraid I would move out of the building
without undoing what I had done. But I remembered and did so the last
week I was there.

Here I have a modern little bathtub and I reversed the overlow plate,
to get about 1 1/2 inches more depth. I turned the overflow, inside
the tub, upside down. I hope I remember to undo it before I move,
although in Brooklyn, it was totally invisible -- there was no need to
pull the pipe up more than a quarter inch. Here one can see the open
drain at the top even before getting in the tub.


Even without modifying the thermostat, how come we don't damage our
A/C's when we have the A/C-Heat switch set to OFF and the Fan switch
set to AUTO or ON?

Or when we have the A/C-Heat switch set to A/C, the thermostat set to
100 degrees (or anything hotter than what the house is), and the Fan
switch set to AUTO or ON?

Can we damage our A/C just by setting the thermostat to settings we
don't always use?

-= HvacTech2 =-


Meirman


Meirman

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or not you are posting the same letter.

Change domain to erols.com, if necessary.
  #25   Report Post  
Peter
 
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Default Thermostat Wiring

On Sat, 02 Aug 2003 15:12:42 -0400, meirman wrote:

What to do next?

Use the relay you are controlling remotely to disconnect the Green
lead of the thermostat from the Green lead of the furnace.

In other words, take the Green lead from the furnace-AC and connect it
to the common connector of a double throw relay switch. In the normal
position, have it connected to the Green lead from the thermostat, as
it is now.****

In the activated position, have it connected to the Red lead from the
thermostat/furnace-AC. Of course you don't have to and can't cut the
Red wire.


Thank you for the answer! It does make sense to me now that I've learned
all that I've learned from this thread. And, I do like the "fail safe"
nature of your design.

The only fly in my ointment now is the relay I have (for my home
automation system) is single-pole, single-throw. There is no connector on
the "normally-open" side so I will have to find another relay that has
contacts on both sides that will work with my home-auto system.

Peter
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meirman
 
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Default Thermostat Wiring

In alt.home.repair on Sat, 02 Aug 2003 15:12:42 -0400 meirman
posted:


But, Peter, if you run a the switch part of a relay in simple shunt
with the ON position of the Fan switch, the power will go (logically
only since it is AC current) in the opposite direction, compared to
the last sentence of the previous paragraph**. That is, when the relay
you add sends 24 volts to the Green wire, that 24 volts would be
present at the AUTO lead of the Fan switch. We know the Fan switch is


I guess these lines are a little backwards, relative to the Fan
switch. ....the 24 volts from the Green wire would be present at the
Common terminal of the Fan switch.

in the AUTO position, because if it were in the ON position, it would
be ON all the time anyhow and Peter would be asking how to turn it
off, not how to turn it on. When the 24 volts reaches the Fan switch
Auto position, it then goes through the switch to the common terminal
of the Fan switch. And then via the internal connection in the


It reaches the Common terminal and then goes through the switch to the
AUTO terminal, and from the AUTO terminal to the Yellow screw/wire.

thermostat, to the Yellow screw/wire, where it goes to the furnace and
activates the cooling relay and cooling function of the AC.



Meirman

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  #27   Report Post  
Stormin Mormon
 
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Default Thermostat Wiring

Yes, you can tell. No, your guesses are incorrect.

How about call a HVAC guy to do it for you?

--

Christopher A. Young
Learn more about Jesus
www.lds.org
www.mormons.org
..
..

"Peter" wrote in message
...
I'd like to find out whether there is any "standard" to the wiring between
home thermostats and the HVAC equipment.

The thermostats in my house are connected to the HVAC units in the
basement via a 5 conductor cable. Yellow, green, white, red, blue.

The blue is not connected. I *assume* that two of the other four are the
main on/off and the other two are for the fan on/auto switch. Can I tell
by color which is which or do I have to open up the thermostat and look?

Thanks.

Peter

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meirman
 
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Default Thermostat Wiring

In alt.home.repair on Sun, 03 Aug 2003 15:33:06 GMT the_plumber
posted:

meirman wrote:

In alt.home.repair on Sat, 02 Aug 2003 15:20:40 GMT the_plumber
posted:

Peter wrote:


OK, I can now see that just connecting an external relay to the red and
green wires is not the right answer.
Peter


Whatever you do, DON'T CUT THE RED WIRE!


Why? What will happen if I d


Due to liability I don't think I should go into it.


This is a friend of the poster Meirman. I'm very sorry to notify you
that he did cut the red wire while he was in the middle of the last
post.

Somehow, the explosion caused his post to be sent, incomplete though
it was. The trauma and burn unit says he may be discharged in about 2
weeks.
  #29   Report Post  
HvacTech2
 
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Default Thermostat Wiring



Hi 'nuther, hope you are having a nice day

On 03-Aug-03 At About 15:20:11, 'nuther Bob wrote to All
Subject: Thermostat Wiring

'B From: 'nuther Bob

'B On Sun, 3 Aug 2003 12:25:11 -0700, "CBHvac"
'B wrote:

'B ....and thats why you are HERE and not in the alt.HVAC
'B group....we ran your silly stupid ass out. Now you are here, tryin
'B to impress those that do not know better.

'B I don't know why you'd run him out of alt.hvac. He chanted the HVAC
'B tech mantra "not for free, not for free".

It's because he doesn't have a clue. you really don't understand what we go
through in this trade. just about everything we work with is extremely
dangerous. I really don't want to see anyone get hurt. it isn't due to money
but the danger involved.


-= HvacTech2 =-


... I'm not really a cowboy. I just found the hat...

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  #30   Report Post  
dyiidiot
 
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Well, I'm not a tech or trainee or even the least bit knowledgable about
anything involving HVAC. I am, however, dealing with this exact same
issue. I am about to move out of an apartment and do not want my
landlord to charge me an ungodly damage fee for A/C that never worked
in the first place. So I have been randomly connecting wires of every
imaginable color hoping to win the deposit-return lottery. Am I lucky
to still be alive and should I cease this activity immediately?


--
dyiidiot
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View this thread: http://www.homeplot.com/showthread.php?t=14329



  #31   Report Post  
SQLit
 
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"dyiidiot" wrote in message
...

Well, I'm not a tech or trainee or even the least bit knowledgable about
anything involving HVAC. I am, however, dealing with this exact same
issue. I am about to move out of an apartment and do not want my
landlord to charge me an ungodly damage fee for A/C that never worked
in the first place. So I have been randomly connecting wires of every
imaginable color hoping to win the deposit-return lottery. Am I lucky
to still be alive and should I cease this activity immediately?


--
dyiidiot



Like the handle...

It is 24 volts at the t-stat. As long as you do not short the wrong ones to
ground or to each other there is little danger to you. Unless your standing
in a bucket of water. (following your handle).

a little googling and you should be able to come up with the wiring diagram
for your t-stat.



  #32   Report Post  
Tim Fischer
 
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It's never a very good idea to go randomly shorting out wires that you have
no idea what they do. Most T-stats are wired up with a common code --
google is your friend...

-Tim


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