Heat Pump Doesn't Work In Cool

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Old 11-29-15, 05:58 AM
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Heat Pump Doesn't Work In Cool

I have a 1998 model Goodman heat pump that won't go into cooling mode. The condenser compressor and fan won't turn on when in cool mode. All I hear is a buzzing sound coming from the contactor. When it's set to heat mode the condenser compressor and fan come on and the unit functions like it should.

The 24v signal to the contactor when placed in cool mode turns on and off repeatedly. This caused the transformer to burn out when I placed it in cool and didn't realize there was a problem.

What can cause the 24v control signal to cycle on and off only when placed in cool mode?
 
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Old 11-29-15, 08:29 AM
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thermostat ? ?
 
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Old 11-29-15, 08:41 AM
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dsomerv has a good point. Have you replaced the thermostat recently?

Another possibility is a shorted "O" wire to the reversing valve.



This often occurs in the outdoor unit where the wire rubs against a copper pipe or a panel.

 
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Old 11-29-15, 08:48 AM
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An Ohm reading across the isolated terminals of a reversing valve should give around 13 to 16 Ohms.

3 Ohms would pop a fuse or cook a transformer. If you had a Carrier or Honeywell digital thermostat a short can sometimes cause the thermostat to continuously click and reset when it is in cool mode.
 
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Old 11-29-15, 12:19 PM
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I'm going to replace the thermostat. I'm getting continuity across the 24v supply and the compressor when in cool mode but am not confident that it isn't switching on and off. I think I could verify with an oscilloscope if I had one.

I'll check the ohms of the reversing valve first though. I only checked it for continuity before.

This whole thing started when my sequencer failed and stuck on. It fried my transformer.

I replaced the transformer but disconnected the sequencer since im waiting on the new ine in the mail.
 
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Old 11-29-15, 12:34 PM
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Y = compressor
G = fan
O = reversing valve in cooling position
R = 24 volts AC
W = heat strips
C = 24 volt common

You can prove thermostat failure by bypassing the thermostat.

Twist R,G,Y and O together at the thermostat to get cooling.



Service techs do not use oscilloscopes. I recommend avoiding bottom of the line thermostats if you decide to replace it.
 
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Old 11-29-15, 01:33 PM
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I'll try the bypass. I need to clarify. I took the thermostat off the wall and turned it to cool(battery powered). I was able to verify that the internal relays on all the applicable wires to the 24v was there. I figured that would at least tell me if the thermostat was commanding 24v to all the necessary cooling wires.
 
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Old 11-29-15, 02:30 PM
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Unless you have a low end digital thermostat installed at this time or you have recently replaced the thermostat, it is unlikely that this is a thermostat problem.
 
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Old 12-20-15, 12:18 PM
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I wanted to reply with the final resolution in case someone else will has the same problem and comes across this thread.

Houston204 nailed it. The reversing valve coil was reading 3 ohms and was drawing too many amps from the transformer causing the compressor contactor to release.

Thanks a lot for the help!
 
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Old 12-20-15, 01:25 PM
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The reversing valve solenoid coil probably smelled like burnt popcorn.

Thanks for posting back with the result.
 
 

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