every night ac starts blowing hot air - http://www.hvacmechanic.com/ Forums
Original message
| fburg
 |  "every night ac starts blowing hot air"
, posted Sat 5 Jul 22:53:  
Three ac companies have looked at this and were all confused. The ac will be running normally for hours and then without anyone touching anything, the unit will start blowing out hot air. We have 3 zones that are connected to a emm-3u honeywell universal minizone panel. The outside unit is a lennox heat pump 12hpb60. When this happens, the minizone panel still has the "cool" light on, but the outside unit has switched to heat. It doesn't make a difference which thermostat/zone is on. This used to happen randomly but for the past 4 days, the ac would work perfect the entire day and then approx 9-10pm at night would start blowing out heat. We'd turn of the unit/breaker/thermostats and turn it back on, but it wouldn't fix the problem. After turning off all the thermostats and leaving them off for the entire night, it would work again the next morning. The last ac company replaced the reversing valve but didn't fix the problem. The emm-3u's yellow purge light flashes which has a description of no zms sensor installed or zms sensor failure. I don't think there's a dats sensor but I'm not sure if that's the same as a zms sensor. Thanks in advance for any suggestions.
[this message was edited by fburg on Sat 5 Jul 22:59] |
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| yatwing
| "Re(1):every night ac starts blowing hot air" , posted Wed 16 Jul 00:14
This happen to me once, but never happen again (knocking on wood) I have a six month old packaged unit which isn't performing up to par in my opinion. Anyways please update with solution if you get it figured out. Good luck
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| TnNATE1412
| "Re(1):every night ac starts blowing hot air" , posted Sun 6 Jul 09:46
I'm not saying this is your problem, but, I have had a zone board to act up, intermittently. I had Honeywell Tech Support go through with me, and after agreeing that the board was the problem, and replacing, their problem was eliminated.
The DATS and ZMS are the same item. If you do not have one installed, the light will flash continuously, regardless of a board problem.
You could possibly have a board relay breaking connection to the reversing valve or wire breaking down. The Lennox heat pump defaults to heating mode, without power to the reversing valve coil, which would explain going into HEAT all of a sudden. The reversing valve coil could also be breaking down, Did they replaced the coil with the valve? If not, I would suggest having them to replace the coil to eliminate that. It's quite inexpensive, as compared to a zone board.
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