Question about Honeywell Programmable Thermostat Heater

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-AC appears in the display of chronotherm III

I have a Honeywell Chronotherm III programmable thermostat. While attempting to adjust the temp I noticed -AC in the display where the temp should be displayed. I replaced the batteries and yet it still won't work. Any ideas?

Thanks,
John

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  • jliso Dec 12, 2008

    Thanks squamos1 really appreciate it ... I will check it out

  • Anonymous May 11, 2009

    Thanks to you


    squamous1

    I got a same problem and by following your advise,, I fixed it ,, be safe

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We had this problem recently. The heater would come on for a minute and the thermostat would display "Hold" plus the temperature. A minute later we would hear a "click" at the thermostat, and then "-AC" would appear where the temperature should be. The heater would then shut off, only to come on again a couple minutes later. The intake was also very loud. Anyway, we found the solution to be simple - my husband decided to just try changing the air filter, and all of a sudden everything was working perfectly! We thought it was a broken thermostat, but thankfully we tried an easier (and what should be obvious) solution.

Posted on Dec 16, 2009

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I have had the same problem- twice. It was a similar but different problem each time. The -AC means the ac control voltage isnt making it to the thermostat. In my case both times it was a switch in the control circuit that wasn't closing properly. The easiest was the front cover switch. If the front cover is removed from the furnace or has vibrated loose, the switch will open, preventing the furnace from running. The other instance I ran into was a flow switch on the exhaust blower which ensures the there is flow OUT the chimney. The switch wasn't functioning, so the furnace wouldn't start. The blower would come on for a short time, but the burners wouldn't light.

Hope this helps,

Posted on Dec 12, 2008

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