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View Full Version : Honeywell RTH7400 seems to have locked my compressor


kspin0404
Mar 2, 2009, 07:14 AM
Woke in the middle of the night and started to adjust the temp. For some reason the thermostat seems to have locked the compressor so I can't get heat at all now! Read the manual three times, reset power to all units, still can't get the heater to kick on. Not a wiring issue because everything was working fine before... Replaced batts too just to be safe! Any help? I got 10 inches of snow and not much hope of getting out anytime soon!

wmproop
Mar 2, 2009, 12:45 PM
Do you have backup/aux. furnace? Set the tstat to emergancy heat,maybe a little more expensive but is better than freezing till you get the heatpump fixed

letmetellu
Mar 2, 2009, 01:13 PM
If you have ten inches of snow on the ground I suspect that your heat pump should not have been running, there is a control in the heat pump that shuts it off after the temp drops below a certain point and the aux heat will kick in. Sounds like a problem with the aux heat. What do you have for aux heat, Electric or gas.

kspin0404
Mar 2, 2009, 01:34 PM
If you have ten inches of snow on the ground I suspect that your heat pump should not have been running, there is a control in the heat pump that shuts it off after the temp drops below a certain point and the aux heat will kick in. Sounds like a problem with the aux heat. What do you have for aux heat, Electric or gas.?

Electric. But the Aux heat setting is lit on the thermo, but the condenser won't kick on.. I tried the fan "on" mode to see if I could get that to start and it wouldn't start either..

kspin0404
Mar 2, 2009, 01:51 PM
do you have backup/aux. furnace? set the tstat to emergancy heat,maybe a little more expensive but is better than freezing till you get the heatpump fixed


Tried this too.. but the condenser will not kick on in either mode..

KC13
Mar 2, 2009, 02:59 PM
Will the indoor fan run if the thermostat fan selector is switched to "ON"? If not, have you tried checking the power supply to the outdoor unit? If control power for the system is supplied by a transformer outdoors, any loss of power to the outdoor unit will bring the whole system down.

kspin0404
Mar 2, 2009, 07:02 PM
No the fan will not run at all.. Plus the unit in the basement on the heat pump is humming, but the reset button will not stay in.. It keeps tripping out.. I suspect that the there is an issue with the outside unit like you said but that could be anywhere I guess.. But we are going to check it in the morning after we dig out! Thanks for your help!

KC13
Mar 3, 2009, 04:40 AM
Reset button? Like a low voltage circuit breaker? Set the thermostat selector to the emergency mode. If the system runs/heats, the problem is at the outdoor unit. I'm thinking... shorted contactor coil.

kspin0404
Mar 3, 2009, 02:08 PM
Reset button? Like a low voltage circuit breaker? Set the thermostat selector to the emergency mode. If the system runs/heats, the problem is at the outdoor unit. I'm thinking...shorted contactor coil.

I tried the reset button on the unit downstairs, but when I throw the breakers on the unit, the reset button trips again..? So I still have nothing..

KC13
Mar 3, 2009, 08:31 PM
Try this: Disconnect 1 wire (any wire except "R") from the thermostat, and press reset button. If it trips, reconnect wire from previous step and disconnect another. Repeat this process until the reset doesn't trip; you've found the shorted circuit.

kspin0404
Mar 4, 2009, 11:51 AM
Try this: Disconnect 1 wire (any wire except "R") from the thermostat, and press reset button. If it trips, reconnect wire from previous step and disconnect another. Repeat this process until the reset doesn't trip; you've found the shorted circuit.

Thanks so much, I will give it a try... Let you know how it turns up..

KC13
Mar 4, 2009, 04:21 PM
Try this: Disconnect 1 wire (any wire except "R") from the thermostat, and press reset button. If it trips, reconnect wire from previous step and disconnect another. Repeat this process until the reset doesn't trip; you've found the shorted circuit.Somewhat trial-and-error, but will save you the costs of a multimeter AND fitness club fees... :p

kspin0404
Mar 4, 2009, 05:34 PM
We found the problem. A bad interface board on the outside unit.. Looks like a mouse got to it.. Replaced it for $478 for parts and labor and I have heat..

KISS
Mar 4, 2009, 09:23 PM
I have no idea why mice like circuit boards. They take out generators too.

KC13
Mar 5, 2009, 01:59 PM
Probably a baby looking for his "motherboard"... :p