heat pump dosnt shut off.

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heat pump dosnt shut off.

Postby ax2ron911 » Sat Jan 05, 2013 12:08 am

I went to check a Goodman heat pump in Virginia. Customer complaint was she would set the thermostat for 62 and when she would come home from work the thermostat and temp was reading 80 and still running. I checked the low voltage at the outdoor unit and the thermostat was still calling for heat. I noticed and added on time delay relay on the condensor. I changed the thermostat out with a new honeywell progamable one. 4 days later the customer is calling back saying its still running she has it set for 62 and its 77.

I went back over to customers house today. I looked at the indoor unit, it was an old 82 GE model, no control board, just relays. The problem seems to be intermittent. I checked for continuity between the red low voltage wire and all the others, no direct short. I turned thermostat to heat and turned it up, I went to the indoor unit and wiggled all the control wiring. The indoor fan motor turned off, the outdoor continued to run. I cut approx 2ft of control wire off, for both the thermo and outdoor. I stripped the 2 ft of wire to look at its condition, it looked in good condition. rewired it all and let her run. Not sure if its going to fix it. i may just have to replace all the wire. i guess the heat strips could have a relay stuck and maybe a contactor in the outdoor is also sticking. Anyone have any ideas?
any ideas? thanks fellas in advance.
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- heat pump dosnt shut off.

Postby Freon » Sat Jan 05, 2013 2:34 pm

The fact the system runs too long does not suggest a broken control wire. With a broken control wire you'd expect the system to stop before reaching the set temperature due to the break in the wire.

I would very closely examine the Goodman heat pump control board and double check the thermostat wiring and jumper configuration. Is the changeover valve being energized for the correct call (heating or cooling). Check the control board for cold solder joints and poor terminal connections.

It is hard to know if the heat causing the overrun of the set temperature is from the heat pump or the heat strips (Aux heat). The indoor air handler and heat strips are simple with, as you observed, a relay for the 240 volt heat strips and a relay for the indoor blower. Usually the indoor blower relay is a DPST with one switch energizing the blower motor and the other energizing the heat strip relay. That way not heat strip power unless the blower is running.

The heat strips usually are called when the house temperature is 2 degrees less than set temperature telling the thermostat the heat pump isn't able to warm the house. But once the set temperature is reached both the heat strips and heat pump should stop. If the relay for the heat strips were welded shut you'd find the heat never turning off.
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- heat pump dosnt shut off.

Postby ax2ron911 » Sun Jan 06, 2013 2:57 am

I like what you said at the end, " if the heat strips relay was welded shut the heat wouldnt turn off.' its possible the heat strips relay is just getting stuck, right? Although it doesnt expain why the indoor fan motor stopped when i manipulated the control wiring right outside the air handler. From what i remember the heat pump condensor was running when the interior was 80 degrees when the thermo was set for 70. Would The heat strip relay also cause the condensor to continute to run? Thanks for the reply.
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- heat pump dosnt shut off.

Postby Freon » Sun Jan 06, 2013 12:17 pm

The heat strips are there to help the condenser so both could be running if the house temp were more than 2 degrees below the set temp. The heat strips are there only as an auxiliary source of heat and it's the thermostat that calls for heat strips when the house temp is more than 2 degrees below the set temp.

The Y lead from the thermostat controls the heat pump. The O wire from the thermostat determines if the heat pump is in AC or Heating mode via the changeover valve. The W2 wire from the thermostat determines when the heat strip relay is activated and the G wire determines when the blower is on AND allows the heat strip relay to be active.

If the heat strip relay were welded, the outdoor condenser would not be on since the thermostat would tell everyone the set temp has been reached. Without the fan the heat strips would overheat and possibly cause a fire. I base that conclusion on the assumption that the high temp limit for the heat strips is wired in series with the heat strip relay's solenoid. Usually if the high limit opens the heat strip relay is deactivated. But if it's welded closed it won't matter.

Based on the above I doubt it's a welded relay. For some reason there's an ongoing call for heat after the set temp is reached. I would carefully check the thermostat and the control wiring looking for a way control wires might short. Check all connections at the air handler even though they're simple pass-through. What model thermostat did you install.
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