Heat Pump will not cut off

sunliner · 05-12-2011, 10:12 PM

Last week I discovered my Ducane HP10B18 heat pump would not cut off. My thermostat a Honeywell T841A1217 was set to cool/auto and when it reached the correct temp the air handler fan cut off but the heat pump continued to run. In my electrical panel there is a breaker for the heat pump and another breaker for the air handler/thermostat, there is also a outside breaker for the heat pump and a disconnect in the attic for the air handler. I use the outside breaker to control the heat pump. I replaced the contactor but unfortunately when I turned the air handler/thermostat breaker back on the contactor energized(the heat pump breaker was off).
I checked the wiring at the heat pump, thermostat, and air handler, I did clean and tighten some contacts but everything appeared proper.

At the Thermostat. With the system switch set to OFF and with the fan switch set to ON the fan operates. With the system switch set to heat/auto the fan runs, Aux heat comes on and the green light operates. With the system switch set to EM heat/auto the fan runs, EM heat comes on and the red light operates. With the system switch set to cool/auto the fan runs. When I move the temperature lever up and down I can hear the relay and fan operate.

At the heat pump. If the air handler/thermostat breaker is off the heat pump will not operate. If the thermostat is set to Off or heat and I turn the outside breaker on the heat pump/fan will run in heat mode. If the thermostat is set to cool and I turn the outside breaker on the heat pump/fan will run in cooling mode. As I mentioned earlier once the thermostat has reached the proper temperature the air handler fan will cut off, yet the heat pump will continue to run. For some reason my control system cannot turn the heat pump off when needed. If anyone can help it would be appreciated. Thanks a lot.

Marty S. · 05-12-2011, 10:31 PM

Check the low voltage circuit with a meter to find out why the contactor is energized. Start at the heat pump and work your way back.

sunliner · 05-13-2011, 10:25 AM

Marty, Thanks for your help. I have low voltage from the heat pump to the thermostat and same to the air handler. I would suspect I have a thermostat problem however I do not have the ability to test it or know how to eliminate it. I do appreciate you taking the time to respond. Thanks again.

Doc Holliday · 05-13-2011, 10:40 AM

Quote:

Originally Posted by sunliner

Marty, Thanks for your help. I have low voltage from the heat pump to the thermostat and same to the air handler. I would suspect I have a thermostat problem however I do not have the ability to test it or know how to eliminate it. I do appreciate you taking the time to respond. Thanks again.

You can test a stat with pretty much no tools.

sunliner · 05-13-2011, 12:30 PM

Doc Holliday, You have my attention. Can you share your procedure? My thermostat is an older model Honeywell T841A1217. Thanks Doc.

Doc Holliday · 05-13-2011, 02:28 PM

All control power is derived from the air handler so regardless the heat pump breaker being on or off, if the call for cool or heat is on through the stat through the air handler than the contactor is supposed to be pulled in, energized.

The breaker is for the high voltage which when the contactor is pulled in via low voltage (call for heat or cool) flows through the contactor, turning the heat pump (compressor) on. If the low voltage is present and calling then again, the contactor will be pulled in and is normal. Now if your stat is in the off position and the contactor is pulled in, then you have a problem.

It appears you have a calling problem of some sort meaning that the call is always on to the heat pump which would indicate either the main low voltage wire is connected to the heat pump or the control signal from the stat is always on to the ehat pump, hinting at a bad stat. The only thing that is right is that the air handler is shutting off at desired set point.

At the stat and while the system is running in cooling mode, remove the wire on the y teminal and see if the outside goes off as well as the inside.
You will need a small screwdriver to loosen the wire at the stat.

Do not let yourself, the wire you are remiving or the screwdriver touch anything else, any other terminal or wire or anything, in that stat.

sunliner · 05-13-2011, 06:38 PM

Doc Holliday, Thank you for your help. I am grateful. I will follow your instructions and let you know results. It will be sometime tomorrow when I can get someone to help me hold the thermostat, and I will be careful. Thanks again, Doc.

sunliner · 05-14-2011, 11:35 AM

Doc Holliday good morning, I was able to accomplish your test. I followed these steps.
A. All breakers were off over night
B. Removerd the thermostat from the wall and set the yellow wire so I could remove It easily.
C. Turned on the air handler/thermostat inside breaker.
D. Moved the temperature lever to cold and the thermostat from off to cool/auto. I could hear the relay click and the fan motor came on.
E. Went to the heat pump and as I came around the corner of the house I thought I heard the contactor click.
F. I turned the outside breaker on the heat pump started and it was in cooling mode.
G. Let the system operate for about five minutes cool air was coming from the vents. Pulled the yellow wire from the thermostat. Air handler was on I looked out the window and the heat pump was still operating.
H. At the thermostat I moved the temperature lever to warm and heard the relay click. Moved system switch to off.
J. Went to heat pump it was in heat mode, I turned the breaker off.
K. All breakers were turned off.

I did a second test and everything was the same until I went outside to turn the heat pump breaker on. This time the heat pump did not come on immediately. It was a couple of minutes before it energized. I suppose it is on a timer or something. I removed the yellow wire, results were the same, heat pump still on air handler on. This time I went outside to make sure the heat pump was still in cooling mode, it was. Moved the system switch to off and went out to check heat pump it was again running in heat mode. Turned all breakers off.

Doc I hope my explanation is helpful to you. Thanks for you expertise and courtesy. I hope you have agood weekend.

sunliner · 05-16-2011, 07:24 PM

Doic Holiday. Have you had an opportunity review my last post? Thanks

hvactech126 · 05-16-2011, 07:45 PM

Check your contactor in the HP it is probably welded closed.

sunliner · 05-16-2011, 10:01 PM

Contactor has been replaced. Original was ok also. Thanks

hvactech126 · 05-16-2011, 10:04 PM

if that is the case then you have a short in your wiring. or a bad defrost control if the low volt runs through it to control the contactor

**beenthere** · 05-17-2011, 05:47 AM

With power off, go to your air handler and remove the yellow wire from the thermostat from the Y terminal. Turn power back on, wait five minutes and see if out door unit runs. If not, then good chance there is a short in your thermostat wire bundle. If it does run, then a good chance there is a short in your low voltage wire bundle to the outdoor unit.

sunliner · 05-17-2011, 06:38 AM

Thanks gentlemen, I will work on your recommendations. Thanks again