So the compressor runs and then at some point the A/C decides to turn on the blower fan. Mine works fine for awhile, but then it starts turning the fan on and then off again, within a few seconds, as if it can't decide whether the coil is cold enough.

On 6/18/2014 10:16 PM, Davej wrote:
So the compressor runs and then at some point the
A/C decides to turn on the blower fan. Mine works fine
for awhile, but then it starts turning the fan on and
then off again, within a few seconds, as if it can't
decide whether the coil is cold enough.


What does your AC service tech say? Why did you
tell the class this information? What would you
like for us to do?

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

On Wednesday, June 18, 2014 10:16:26 PM UTC-4, Davej wrote:
So the compressor runs and then at some point the A/C decides to turn on the blower fan. Mine works fine for awhile, but then it starts turning the fan on and then off again, within a few seconds, as if it can't decide whether the coil is cold enough.

Are we talking about a central AC system that's part of
a furnace? A window unit? A mini-split?

IDK what the latter does, but in all the first two types
that I've seen, the coil temp doesn't control the blower.
The blower is turned on and the compressor start at the
same time. When it shuts off, the blower typically stays
on for another minute or two after the compressor goes
off.

On Thursday, June 19, 2014 6:39:38 AM UTC-5, trader_4 wrote:
On Wednesday, June 18, 2014 10:16:26 PM UTC-4, Davej wrote:

So the compressor runs and then at some point the A/C
decides to turn on the blower fan. Mine works fine for
awhile, but then it starts turning the fan on and then
off again, within a few seconds, as if it can't decide
whether the coil is cold enough.


Are we talking about a central AC system that's part of
a furnace?

Yes

IDK what the latter does, but in all the first two types
that I've seen, the coil temp doesn't control the blower.
The blower is turned on and the compressor start at the
same time. When it shuts off, the blower typically stays
on for another minute or two after the compressor goes
off.


Hmmm, you're right. I thought it worked identical to the furnace but apparently not. I've had this strange blower fan operation ever since the furnace was installed and have used continuous fan to avoid it, but now even continuous fan has strange behavior.

On Thursday, June 19, 2014 7:50:37 AM UTC-4, Davej wrote:
On Thursday, June 19, 2014 6:39:38 AM UTC-5, trader_4 wrote:

On Wednesday, June 18, 2014 10:16:26 PM UTC-4, Davej wrote:



So the compressor runs and then at some point the A/C

decides to turn on the blower fan. Mine works fine for

awhile, but then it starts turning the fan on and then

off again, within a few seconds, as if it can't decide

whether the coil is cold enough.





Are we talking about a central AC system that's part of

a furnace?



Yes



IDK what the latter does, but in all the first two types

that I've seen, the coil temp doesn't control the blower.

The blower is turned on and the compressor start at the

same time. When it shuts off, the blower typically stays

on for another minute or two after the compressor goes

off.





Hmmm, you're right. I thought it worked identical to the furnace but apparently not. I've had this strange blower fan operation ever since the furnace was installed and have used continuous fan to avoid it, but now even continuous fan has strange behavior.

You need to put a meter on it and see if it's getting power but not running or if the control board is not keeping it powered.

On Thursday, June 19, 2014 8:25:22 AM UTC-4, jamesgang wrote:
On Thursday, June 19, 2014 7:50:37 AM UTC-4, Davej wrote:

On Thursday, June 19, 2014 6:39:38 AM UTC-5, trader_4 wrote:



On Wednesday, June 18, 2014 10:16:26 PM UTC-4, Davej wrote:







So the compressor runs and then at some point the A/C



decides to turn on the blower fan. Mine works fine for



awhile, but then it starts turning the fan on and then



off again, within a few seconds, as if it can't decide



whether the coil is cold enough.











Are we talking about a central AC system that's part of



a furnace?







Yes







IDK what the latter does, but in all the first two types



that I've seen, the coil temp doesn't control the blower.



The blower is turned on and the compressor start at the



same time. When it shuts off, the blower typically stays



on for another minute or two after the compressor goes



off.











Hmmm, you're right. I thought it worked identical to the furnace but apparently not. I've had this strange blower fan operation ever since the furnace was installed and have used continuous fan to avoid it, but now even continuous fan has strange behavior.



You need to put a meter on it and see if it's getting power but not running or if the control board is not keeping it powered.

Agree, that would be a good place to start. Also, if it;s a modern unit,
they have LEDs that light to indicate OK or identify faults if the CPU
board knows there is one.

Running the fan constantly may not be such a good idea either. In furnaces
from 25 years ago, putting the fan on all the time put it on high, the
same speed as for cooling. Which is OK, except that those motors were
not efficient and it's going to run up $$$, running when it doesn't need to..

Newer furnaces, the blower when set to run all the time, doesn't run
at high speed. Mine runs closer to the heating speed. That isn't going
to produce maximum cooling. With mine, if the AC kicks on, then it goes
up to high. With the OP system with the problem, without knowing how
it operates no way to know what it does.

trader_4 wrote:
On Thursday, June 19, 2014 8:25:22 AM UTC-4, jamesgang wrote:
On Thursday, June 19, 2014 7:50:37 AM UTC-4, Davej wrote:

On Thursday, June 19, 2014 6:39:38 AM UTC-5, trader_4 wrote:



On Wednesday, June 18, 2014 10:16:26 PM UTC-4, Davej wrote:







So the compressor runs and then at some point the A/C



decides to turn on the blower fan. Mine works fine for



awhile, but then it starts turning the fan on and then



off again, within a few seconds, as if it can't decide



whether the coil is cold enough.











Are we talking about a central AC system that's part of



a furnace?







Yes







IDK what the latter does, but in all the first two types



that I've seen, the coil temp doesn't control the blower.



The blower is turned on and the compressor start at the



same time. When it shuts off, the blower typically stays



on for another minute or two after the compressor goes



off.











Hmmm, you're right. I thought it worked identical to the furnace but apparently not. I've had this strange blower fan operation ever since the furnace was installed and have used continuous fan to avoid it, but now even continuous fan has strange behavior.



You need to put a meter on it and see if it's getting power but not running or if the control board is not keeping it powered.

Agree, that would be a good place to start. Also, if it;s a modern unit,
they have LEDs that light to indicate OK or identify faults if the CPU
board knows there is one.

Running the fan constantly may not be such a good idea either. In furnaces
from 25 years ago, putting the fan on all the time put it on high, the
same speed as for cooling. Which is OK, except that those motors were
not efficient and it's going to run up $$$, running when it doesn't need to.

Newer furnaces, the blower when set to run all the time, doesn't run
at high speed. Mine runs closer to the heating speed. That isn't going
to produce maximum cooling. With mine, if the AC kicks on, then it goes
up to high. With the OP system with the problem, without knowing how
it operates no way to know what it does.

OP did not even mention what set up he has. Set the fan to auto mode and
tried?

"Davej" wrote in message
...
So the compressor runs and then at some point the A/C decides to turn on
the blower fan. Mine works fine for awhile, but then it starts turning the
fan on and then off again, within a few seconds, as if it can't decide
whether the coil is cold enough.


The way the companies dick around with settings to meet certain seer
ratings, it would not surprise me that the blower is set up to only come on
when a certain head pressure or coil temperature is reached. Probably not
your case, but could be.

That is one reason why the fans ramp up in speed instead of comming on and
just have one speed for heating and anther for cooling in a heat pump.

On Thursday, June 19, 2014 11:39:52 AM UTC-4, Ralph Mowery wrote:
"Davej" wrote in message

...

So the compressor runs and then at some point the A/C decides to turn on

the blower fan. Mine works fine for awhile, but then it starts turning the

fan on and then off again, within a few seconds, as if it can't decide

whether the coil is cold enough.





The way the companies dick around with settings to meet certain seer

ratings, it would not surprise me that the blower is set up to only come on

when a certain head pressure or coil temperature is reached. Probably not

your case, but could be.


I've never seen such a thing and doubt it exists.
It certainly wouldn't be based on temperature or
pressure, because the controller in the furnace isn't
measuring either of those. It could have a time delay,
but every system I've seen the blower starts at the same
time as the compressor. My new Rheem ramps up over
about 30 secs, but it starts same time as the compressor.
The coil is cold very quickly. Without knowing exactly
how they calculate the SEER, it's just speculation that
a 30 sec or 1 min delay would even have any effect at all
on the SEER.


That is one reason why the fans ramp up in speed instead of comming on and


Your source for that? I thought the reason variable
speeds ramp up is because they can and it makes the
blower far less noticeable when it starts up.


just have one speed for heating and anther for cooling in a heat pump.

IDK about heat pumps, but my Rheem has multiple jumper selectable
speeds for both heating and cooling. The heating speed in
every furnace I've seen has always been less than for cooling.

On Thursday, June 19, 2014 8:16:15 AM UTC-5, trader_4 wrote:
On Thursday, June 19, 2014 8:25:22 AM UTC-4, jamesgang wrote:
On Thursday, June 19, 2014 7:50:37 AM UTC-4, Davej wrote:
On Thursday, June 19, 2014 6:39:38 AM UTC-5, trader_4 wrote:
On Wednesday, June 18, 2014 10:16:26 PM UTC-4, Davej wrote:

So the compressor runs and then at some point the A/C
decides to turn on the blower fan. Mine works fine for
awhile, but then it starts turning the fan on and then
off again, within a few seconds, as if it can't decide
whether the coil is cold enough.

Are we talking about a central AC system that's part of
a furnace?

Yes

IDK what the latter does, but in all the first two types
that I've seen, the coil temp doesn't control the blower.
The blower is turned on and the compressor start at the
same time. When it shuts off, the blower typically stays
on for another minute or two after the compressor goes
off.

Hmmm, you're right. I thought it worked identical to the
furnace but apparently not. I've had this strange blower
fan operation ever since the furnace was installed and
have used continuous fan to avoid it, but now even
continuous fan has strange behavior.

You need to put a meter on it and see if it's getting
power but not running or if the control board is not
keeping it powered.

Agree, that would be a good place to start. Also, if
it's a modern unit, they have LEDs that light to indicate
OK or identify faults if the CPU board knows there is one.

Running the fan constantly may not be such a good idea
either. In furnaces from 25 years ago, putting the fan
on all the time put it on high, the same speed as for
cooling. Which is OK, except that those motors were
not efficient and it's going to run up $$$, running when
it doesn't need to.

Newer furnaces, the blower when set to run all the time,
doesn't run at high speed. Mine runs closer to the heating
speed. That isn't going to produce maximum cooling. With
mine, if the AC kicks on, then it goes up to high. With the
OP system with the problem, without knowing how it operates
no way to know what it does.


The symptom has cured itself for the past few days. When the symptom was occurring I could hear a relay clicking on the furnace board, so it was definitely deciding to turn the blower fan on and off. Also the blower fan motor was cool to the touch. The furnace controller terminal voltages never changed: Red had 26VAC and Green had 20VAC continuously.

I think the first thing I should do is get the thing wired correctly because I suspect that it has never been wired correctly.

Davej wrote:
On Thursday, June 19, 2014 8:16:15 AM UTC-5, trader_4 wrote:
On Thursday, June 19, 2014 8:25:22 AM UTC-4, jamesgang wrote:
On Thursday, June 19, 2014 7:50:37 AM UTC-4, Davej wrote:
On Thursday, June 19, 2014 6:39:38 AM UTC-5, trader_4 wrote:
On Wednesday, June 18, 2014 10:16:26 PM UTC-4, Davej wrote:

So the compressor runs and then at some point the A/C
decides to turn on the blower fan. Mine works fine for
awhile, but then it starts turning the fan on and then
off again, within a few seconds, as if it can't decide
whether the coil is cold enough.

Are we talking about a central AC system that's part of
a furnace?

Yes

IDK what the latter does, but in all the first two types
that I've seen, the coil temp doesn't control the blower.
The blower is turned on and the compressor start at the
same time. When it shuts off, the blower typically stays
on for another minute or two after the compressor goes
off.

Hmmm, you're right. I thought it worked identical to the
furnace but apparently not. I've had this strange blower
fan operation ever since the furnace was installed and
have used continuous fan to avoid it, but now even
continuous fan has strange behavior.

You need to put a meter on it and see if it's getting
power but not running or if the control board is not
keeping it powered.

Agree, that would be a good place to start. Also, if
it's a modern unit, they have LEDs that light to indicate
OK or identify faults if the CPU board knows there is one.

Running the fan constantly may not be such a good idea
either. In furnaces from 25 years ago, putting the fan
on all the time put it on high, the same speed as for
cooling. Which is OK, except that those motors were
not efficient and it's going to run up $$$, running when
it doesn't need to.

Newer furnaces, the blower when set to run all the time,
doesn't run at high speed. Mine runs closer to the heating
speed. That isn't going to produce maximum cooling. With
mine, if the AC kicks on, then it goes up to high. With the
OP system with the problem, without knowing how it operates
no way to know what it does.


The symptom has cured itself for the past few days. When the symptom was occurring I could hear a relay clicking on the furnace board, so it was definitely deciding to turn the blower fan on and off. Also the blower fan motor was cool to the touch. The furnace controller terminal voltages never changed: Red had 26VAC and Green had 20VAC continuously.

I think the first thing I should do is get the thing wired correctly because I suspect that it has never been wired correctly.

Hi,
On most control board you cn adjust blower torun off delay. You an
increase it. Mine is set at 120 secs. to get the last drop of hot or
cold air out.