Why do a/c thermostats have 5 wires?
 

I would guess they need three: one for cooling part, one for the fan,
and one neutral.

So why 5?

Thanks!

Why do a/c thermostats have 5 wires?
 

On Jul 18, 2:30*am, Aaron Fude wrote:
I would guess they need three: one for cooling part, one for the fan,
and one neutral.

So why 5?

Thanks!

You need 5 if its a combination heating/cooling system, otherwise if
its strictly for cooling, you only need 3.

Why do a/c thermostats have 5 wires?
 

Some systems use two transformers and thus two "hots." RH for heating,
RC for cooling. If the system only has one transformer, the thermostat
has a jumper to go between RH and RC.

So, to get to five wires you'd have

RH Hot for heat
RC Hot for cooling
Yellow for compressor
White for heat
Black for common (to power the clock and electronics in a setback T
stat

Why do a/c thermostats have 5 wires?
 

On Jul 18, 4:07*pm, Rick-Meister wrote:
Some systems use two transformers and thus two "hots." RH for heating,
RC for cooling. If the system only has one transformer, the thermostat
has a jumper to go between RH and RC.

So, to get to five wires you'd have

RH Hot for heat
RC Hot for cooling
Yellow for compressor
White for heat
Black for common (to power the clock and electronics in a setback T
stat


Actually, my thermostat is strictly for cooling and it still has five
wires. Thus my question.

Thanks.

Why do a/c thermostats have 5 wires?
 

Aaron Fude wrote:

On Jul 18, 4:07 pm, Rick-Meister wrote:

Some systems use two transformers and thus two "hots." RH for heating,
RC for cooling. If the system only has one transformer, the thermostat
has a jumper to go between RH and RC.

So, to get to five wires you'd have

RH Hot for heat
RC Hot for cooling
Yellow for compressor
White for heat
Black for common (to power the clock and electronics in a setback T
stat



Actually, my thermostat is strictly for cooling and it still has five
wires. Thus my question.

Thanks.

Hot, common, fan, cool makes four. Perhaps the fifth isn't really
functional. What are the terminals to which they're connected labeled?

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Why do a/c thermostats have 5 wires?
 

In case one breaks. Spare wire within the bundle.

Cause it's what the installer had on the truck.

To generate questions.

Obscure building code.

Cause the installer got a good price.

Any or all of the above.

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


"Aaron Fude" wrote in message
...
On Jul 18, 4:07 pm, Rick-Meister wrote:
Some systems use two transformers and thus two "hots." RH for heating,
RC for cooling. If the system only has one transformer, the thermostat
has a jumper to go between RH and RC.

So, to get to five wires you'd have

RH Hot for heat
RC Hot for cooling
Yellow for compressor
White for heat
Black for common (to power the clock and electronics in a setback T
stat


Actually, my thermostat is strictly for cooling and it still has five
wires. Thus my question.

Thanks.

Why do a/c thermostats have 5 wires?
 

Fifth wire can be transformer power, to supply power to the electronic stat.

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


"CJT" wrote in message
...


Hot, common, fan, cool makes four. Perhaps the fifth isn't really
functional. What are the terminals to which they're connected labeled?

Why do a/c thermostats have 5 wires?
 

And the guy with that email adress is solidly PO'd at you for spamming him
with all your group replies.

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


"CJT" wrote in message
...

The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Why do a/c thermostats have 5 wires?
 

Stormin Mormon wrote:

Fifth wire can be transformer power, to supply power to the electronic stat.

i.e. what I called "hot"

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Why do a/c thermostats have 5 wires?
 

On Thu, 17 Jul 2008 23:30:47 -0700 (PDT), Aaron Fude
wrote:

I would guess they need three: one for cooling part, one for the fan,
and one neutral.


It's hot not neutral. The common wire to a group of switches (which
the thermostat is) is normally hot. In the case of normal thermostats,
that's 24VAC 1A max.

So why 5?


How many wires are actually connected to the thermostat? Maybe the
installer had some 5-conductor wire, and used that to save money. The
wire coming out of my furnace is 8-conductor. The other 4 aren't
connected to anything.

Thanks!

I usually see 4: 24VAC supply, heat, cool, fan.

An additional wire might be for a multi-speed compressor, or heat-pump
changeover valve.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

Why do a/c thermostats have 5 wires?
 

Aaron Fude wrote:
I would guess they need three: one for cooling part, one for the fan,
and one neutral.

So why 5?

Thanks!

Years ago I learned the following:
Red = Hot = Power (24 volt) = R terminal
Green = Go = Blower = G terminal
White = Snow = Heat = W terminal
Yellow = Sun = A/C = Y terminal
Blue = Cool = A/C (If there is no Yellow wire) = Y terminal
The 5th wire = Common = C terminal

--
Moe Jones
http://www.MoeJones.info

Why do a/c thermostats have 5 wires?
 

On Sat, 19 Jul 2008 10:21:56 -0500, "Moe Jones"
wrote:

Aaron Fude wrote:
I would guess they need three: one for cooling part, one for the fan,
and one neutral.

So why 5?

Thanks!

Years ago I learned the following:
Red = Hot = Power (24 volt) = R terminal
Green = Go = Blower = G terminal
White = Snow = Heat = W terminal
Yellow = Sun = A/C = Y terminal
Blue = Cool = A/C (If there is no Yellow wire) = Y terminal
The 5th wire = Common = C terminal

The wires coming from my furnace are red, white, green, and gray
(could have been blue once?). This is the cable that has 4 extra
wires: orange, black, brown, yellow (not connected to anything).

I think the color code you gave is standard. I guess whoever put this
in had some extra wire like that.

The only system I've seen with C connected to the thermostat was one
where I added that connection because of thermostat I added required
it. On other systems, C (from the furnace) is connected to the
compressor only.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

Why do a/c thermostats have 5 wires?
 

Mark Lloyd wrote:
On Sat, 19 Jul 2008 10:21:56 -0500, "Moe Jones"

The wires coming from my furnace are red, white, green, and gray
(could have been blue once?). This is the cable that has 4 extra
wires: orange, black, brown, yellow (not connected to anything).

I think the color code you gave is standard. I guess whoever put this
in had some extra wire like that.

If we are talking 24 volt wiring it is OK to have the extra wiring incase
one of them go bad you can use the extra wiring.

When it comes to the C terminal, you use it on the subbase when the stat
needs the common conection so it sounds like you have a standard cool / heat
stat.
--
Moe Jones
http://www.MoeJones.info

Why do a/c thermostats have 5 wires?
 

Most that I have seen use 2 transformers, one for A/C one for heat.

So that would be 2 wires for A/C and 2 wires for heat with a 5th wire for
fan controls. Power for the clock and electronics is picked up from one of
the wires supplying either A/C or heat.


"Rick-Meister" wrote in message
...
Some systems use two transformers and thus two "hots." RH for heating,
RC for cooling. If the system only has one transformer, the thermostat
has a jumper to go between RH and RC.

So, to get to five wires you'd have

RH Hot for heat
RC Hot for cooling
Yellow for compressor
White for heat
Black for common (to power the clock and electronics in a setback T
stat

Why do a/c thermostats have 5 wires?
 

EXT wrote:
Most that I have seen use 2 transformers, one for A/C one for heat.

So that would be 2 wires for A/C and 2 wires for heat with a 5th wire
for fan controls. Power for the clock and electronics is picked up
from one of the wires supplying either A/C or heat.

The 2 transformerwas the older style of control wiring where the wiring
coming from the condensing unit was a 3 wire hook up. One of the wires went
to the thermostat to the RC terminal and one went to the Y terminal and the
third was going to the common of the transformer in the condensing unit.
This meant that the transformer in the condensing unit operated the blower,
in the house, and the condensing unit outside.
The transformer in the furnace would operate the heat only.
--
Moe Jones
http://www.MoeJones.info

Why do a/c thermostats have 5 wires?
 

On Sat, 19 Jul 2008 13:32:35 -0500, "Moe Jones"
wrote:

Mark Lloyd wrote:
On Sat, 19 Jul 2008 10:21:56 -0500, "Moe Jones"

The wires coming from my furnace are red, white, green, and gray
(could have been blue once?). This is the cable that has 4 extra
wires: orange, black, brown, yellow (not connected to anything).

I think the color code you gave is standard. I guess whoever put this
in had some extra wire like that.

If we are talking 24 volt wiring it is OK to have the extra wiring incase
one of them go bad you can use the extra wiring.

When it comes to the C terminal, you use it on the subbase when the stat
needs the common conection so it sounds like you have a standard cool / heat
stat.

Yes.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy