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Old 07-29-2020, 09:17 AM   #16
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


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It's not that. Issue reoccured again at 2am.
something else is triggering emergency heat.��
Emergency heat (auxiliary heat) is triggered by a few things.
In cold climates, when the heat pump cannot keep up the emergency heat will come on if the temperature outside is too cold for the heat pump to work efficiently or if the heat pump is not raising the room temperature as quickly as settings call for. Also during a defrost cycle the emergency / auxillary heat will come on to counter the cooling process.
The latter is controlled by a thermostat in the outside unit, the other circumstances are controlled by the thermostat and the controller circuit.
If it started a couple of weeks back with no human interaction it can be any of these things. Unfortunately it is time to call for service.
How long ago was that t-stat installed?
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Old 07-29-2020, 09:49 AM   #17
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


Use the right terminology.

Emergency heat is really a mode the t-stat has which bypasses the heatpump and turns on the aux heat directly instead.

Aux heat = heat strips and they can be activated by a defrost cycle, call for supplemental heat, or emergency heat mode.
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Old 07-29-2020, 09:54 AM   #18
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


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Use the right terminology.
Funny how all know it all's are inherently smart asses as well.
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Old 07-29-2020, 10:00 AM   #19
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


^There's a reason to use the right terminology in this case -> there are people who read this stuff and think "oh, if my heatpump is running continuously, it's ineffective* due to being too cold outside and I need to switch to emergency heat."

I don't want them switching to emergency heat and getting hit with huge electric bills. (the same people who read and believe that equipment is sized by BTU per sq ft)

*BTW they're perfectly effective when supplemental heat is required, the COP is often still respectable down to 10F or lower but there just isn't enough capacity. "Running too long" isn't a thing either - either the unit supplies enough heat running continuously or it doesn't and needs some help.
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Old 07-29-2020, 10:04 AM   #20
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


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It's not that. Issue reoccured again at 2am.
something else is triggering emergency heat.��

So you're saying it happened with the aux heat t-stat wire disconnected?

It could be the defrost board sending signal to turn on the strips when it shouldn't be.

You can catch it and use a meter to see what's going on or disconnect and insulate/tape off the wire connected to D/W1 on the board in the outdoor unit.
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Old 07-29-2020, 10:44 PM   #21
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


I disconnected and tape off the wire connected to D/W1 on the defrost board.

now waiting and watching.
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Old 08-01-2020, 03:36 PM   #22
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


No heating issues after disconnecting AUX wire from defrost controller.

what is next Change defrost board or ambient temp sensor?
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Old 08-01-2020, 03:51 PM   #23
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


defrost board should never be initiating a defrost and sending power to turn on the aux heat in cooling mode. must be bad.
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Old 08-06-2020, 08:18 AM   #24
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


I replace the board. It did not fix the problem.
Last night same thing happened with new board.

only thing works, If i remove pin from AUX on defrost board. but that will be an issue in winter.
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Old 08-06-2020, 11:29 AM   #25
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


can't think of anything other than a bad board that would cause this problem - unless it's not actually the board that's doing it and something else is energizing the aux heat.

may have just been a coincidence - disconnected that and problem just didn't occur.

the only way to tell for sure is catch it when the problem occurs and check it with a meter, see if that terminal is getting energized with no wire connected.

very odd problem, difficult to track down.
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Old 08-06-2020, 06:45 PM   #26
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


Does the outdoor unit have a low-temperature thermostat that switches the system to aux heat in very cold weather? If so, it may be faulty.
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Old 08-06-2020, 08:17 PM   #27
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


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Does the outdoor unit have a low-temperature thermostat that switches the system to aux heat in very cold weather? If so, it may be faulty.
7.3 PROTECTION FUNCTION INTRODUCTION (Heat pump only)

Sensor T3 (condenser pipe temperature) and T4 (outdoor ambient temperature) When open-circuit, compressor, outdoor fan motor and reverse valve will be OFF. T3>149F,compressor stop working ; T3<140F,compressor start working. When T4 < 5 F, compressor will stop.If the electrical heater kit is installed in the indoor unit, the outdoor unit would provide a signal to drive up the heater. When T4 > 10.4 F, the compressor will restart.
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Old 08-06-2020, 10:55 PM   #28
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


The following is offered as a possibility and not necessarily what your problem may be. If the improper heat is being produced when the compressor is running, this may be useful. If the heat is coming on when the compressor is not running, then you can ignore the advice below.

You may have a sticky or sluggish reversing valve. Remove the operator coil from it and disconnect the wiring harness so it doesn't get hot and short out. Replace it with a reversing valve test magnet and run it that way to see if the problem is no longer present.

FYI, stopping and restarting the system exercises the reversing valve, if cool mode is being called. That can make a sluggish valve work until the next failure. Since it's a pilot pressure operated device, it will be more apt to fail when the head pressure is lowest, such as in the middle of the night.
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Old 08-08-2020, 09:39 PM   #29
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


You would really need to get a meter and test when it occurs, but it seems like you are going through the process of elimination.


-With the W1 wire disconnected at the thermostat, the problem still occurs. I don't think that stat has a E terminal Correct me if I'm wrong.

-With the Aux heat wire disconnected at defrost board, you didn't have the issue. Nevertheless, the new board didn't resolve the issue, so you can rule that out.



I would look for an intermittent short. You may be getting a short from the white wire to the red wire intermittently. Look at the tstat wire coming through any metal. Also, check to see if a string trimmer may have hit the line outside.


You could disconnect the W wire (aux heat) at the air handler. You should see the thermostat wire and condenser wire coming into the air handler.


-Disconnect both of them and see if the problem persists.
-If not, then connect the W1 wire at the air handler that is leading to the thermostat.
-If the problem still isn't present, connect the condenser wire as well.
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Old 08-09-2020, 01:38 AM   #30
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Re: AC blows Hot air at night - Stop and Start fixes it for a while


Defrost stat could be defective.
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