Carrier heat pump not responding to thermostat

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Old 12-27-14, 05:04 AM
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Carrier heat pump not responding to thermostat

Hi. I'm hoping someone has a clue where I should go from here...

I have a Carrier heat pump model #38S6G042300 (defrost board model #CEPL130433-01). A few days ago, our heat pump stopped working and a technician came out to find the problem. After checking things out he said we seem to have a bad defrost board, because he said the little 5 amp fuse inside the indoor unit would blow whenever the defrost board was connected. Anyway, I found the part online and installed it myself, and reconnected the low voltage wires that go out to the out to the heat pump. I also replaced the contactor at the same time. Afterward, everything seemed to work fine -- the compressor would turn on and off according to the thermostat's calls for heat and we got heat through our indoor vents.

It seemed to worked OK for about a day, and now the heat pump won't turn on. I suspect whatever happened before my call to the technician may have happened again. I can hear our Honeywell thermostat click as if it's doing its thing, it changes its display to say "Heat On", and then immediately it will show the word "Wait", which means it's doing it's cool-down thing. I can stand there and about 5 minutes later, the thermostat display will again change to say "Heat On" and click, and then again change to "Wait". This cycle happens continually. Out at the heat pump, I can take a stick and push the contactor button in to engage it and the fan starts up and runs so long as I hold the button in, so it seems it's just not responding to the indoor thermostat. (I now have the thermostat set to Em. Heat for the time being so we have some heat, and that works fine but I know it's costing me!)

What should I try next? Could it be the capacitor? I wouldn't think so since I can manually engage the contactor and it runs.
 
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Old 12-27-14, 10:11 AM
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Check the 24 volt wire to the reversing valve. It commonly rubs the insulation off against a copper pipe or a panel.



If that checks out okay, get an ohm reading across the reversing valve coil.



I would expect ~ 12 to 16 ohms. I have seen 3 ohms pop a low voltage fuse.


That model number does not bring up any heat pumps.
 

Last edited by Houston204; 12-27-14 at 03:39 PM.
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Old 12-27-14, 06:33 PM
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I've run into the exact same problem on a Bryant heat pump. The wire marked with the arrow will chaffe and short to the copper. I put a small piece of automotive heater hose around the wires after repair at that point before I secure them to the pipe this prevents the problem from coming back.
 
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Old 12-28-14, 03:44 AM
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OK, yesterday it miraculously started working again, and the only thing I've done is cut the breakers for about a minute and then turn them back on -- I heard that will "reboot" some systems. Immediately after that, things didn't seem to change -- I observed the same behavior -- but then sometime later in the day I noticed the heat pump was running and everything seemed OK again.

I wonder if a wire short like the one you mentioned would explain the inconsistent behavior, sometimes shorting and sometimes moved away and not shorting.
 
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Old 12-28-14, 05:35 AM
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If there is indeed a short it should be clearing a fuse, check all the connections ,wire nuts and pull off and reinstall any other terminations.
Geo
 
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Old 12-28-14, 10:34 AM
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Yes, a short should blow the fuse. Turning off the breaker & turning it back on will indeed 'reset' the contol board on some equipment. Is your thermostat battery powered or is there a wire going to the 'C' terminal?
 
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Old 01-08-15, 08:15 AM
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Yes, the thermostat does have batteries for backup power and can also supposedly get power through the connected C wire.

Unfortunately yesterday the problem returned, after working fine for about two weeks, and I haven't changed anything. Same behavior as before: I can hear our Honeywell thermostat click as if it's doing its thing, it changes its display to say "Heat On", and then immediately it will show the word "Wait", which means it's doing it's cool-down thing. I can stand there and about 5 minutes later, the thermostat display will again change to say "Heat On" and click, and then again change to "Wait". This cycle happens continually.

I'll try to locate that wire that was mentioned and check for a short, and I'll disconnect and reconnect stuff. Should I rule out the capacitor as being the problem since I can manually engage the contactor? Should I try to find fuse(s) somewhere at the heat pump? Only fuse I've seen is in the blower unit inside the house.

Thanks for the help so far, appreciate it.
 
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Old 01-08-15, 08:30 AM
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What model Tstat do you have?
Geo
 
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Old 01-08-15, 09:15 AM
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The thermostat model is RTH7500, which I installed after all this started.
 
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Old 01-08-15, 12:06 PM
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I disconnected and reconnected all wires to the defrost board, capacitor, and the wire nuts where the low-voltage comes out there, left it and the blower powered off for at least a few minutes, and now some time later it's working again. Crazy thing. Wonder how long it will last this time.
 
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Old 01-08-15, 12:40 PM
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I so love intermittent problems. NOT
 
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Old 01-08-15, 05:10 PM
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It is common to see Honeywell stats jump to the Wait display when they short to ground. This often occurs fast enough to save the low voltage fuse.

Have you inspected for cuts on the control wire yet?






 
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