[SOLVED] Honeywell Chronotherm III - AC Solved

AC means there is no power to the thermostat. It could be that the circuit breaker is off or tripped, or your low voltage transformer (to your air handler, furnace, or whatever you have) is bad. Does the fan come on when you switch the fan switch from 'auto' to 'on'? If not, you have a power problem (in other words, the 'AC' does not stand for Air Conditioning).

The flashing 'temp' means that you have adjusted the temperature away from whatever you have programmed.

Alex, I am somewhat of an expert on thermostats. If it is flashing "- AC" it is quite a simple fix. It just means the Air Cond will not work. Usually you just have to put in fresh batteries. If it is flashing "TEMPORARY" it just means that .....temporarily, the A/C will not work. Both messages are really working together. You often have to replace the thermostat if both messages are showing. Bubba

Go to your local big box store and buy a can of electronspray. Carefully remove the stat and spray the red an blue wires.

big_dgreen had written this in response to

AC could be a diagnostic code from the air handler to the t-stat to alert you of a problemm.

I agree with the info about possibly losing low voltage from your transformer. If the ac is not running you should call a service man.

If it is running, it may be a filter reminder, but I doubt it. I'm not familiar with the chronotherms layout.

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replying to Bubba, Yer Mom wrote: This is wrong! The "-AC" on the Chromotherm III display means the thermostat is not getting the 24V AC power it needs to function. It has nothing to do with Air Conditioning. (This, IMHO, is absoultely horrible product design... but that's what it is :-))

replying to big_dgreen, msstockton wrote: Mine only happens when i go from air to heat. It gets all screwed up and I can't get it to change back no matter what I try

replying to Dr. Hardcrab, m smith wrote: Good information, thanks. In my case, the cover on the furnace was open, so a safety interlock preventing furnace operation caused the thermostat display to essentially disappear, but it intermittently and weakly displayed the -AC code. Attaching the furnace cover solved the problem for me.