Question about Honeywell Power Humidifier: Furnace Humidifier/ Humidifier
Yes, I have a problem on my Honeywell Chronotherm III t-stat - showing "-AC" on top right hand corner, where used to be current temp. The t-stat is used to control both AC and heater, and the problem happens on both "heat" and "cool" setting. I have tried to switch the front part from another working t-stat with same model, it has the same problem. But If it's not a problem on t-stat, how can both AC and heater have problem at same time? Can anyone help? Thanks.
What you can do is try and clean the contacts. Open the door on the thermistat and remove the two screws, after that you can seperate the part that is mounted to the wall and the front panel. Look at the part that is mounted on the wall and you'll see the contacts that should be a copper color. They might be black from age. Clean them and you'll be surprised how well it will work after that.
Denis
Posted on Mar 15, 2009
We have a Chronotherm III thermostat with back-up batteries and Power Save. It was displaying the —AC error message. No heat in December.
We checked the switch, batteries and cleaned the connections. Nothing. Then we remembered we had serviced the furnace air filter and checked the furnace for issues. We reseated the furnace cover after checking it out, and it all works fine now. Apparently one of the covers was not quite true. Blessed heat.
Posted on Dec 16, 2019
Posting my experience in case anyone else is troubleshooting their own problem.
I have a Chronotherm iii thermostat that recently had the 'hold -ac' problem.
The a/c would work fine for hours, but then cut off at the hottest time of the day.
The thermostat's display would be very faint, almost unreadably so.
This happened once before and that time I had to call a tech to come look at the problem.
That time the issue was that the float switch was being engaged due to the drain hole getting blocked after some roof work was done and debris blocked the hole.
I checked those parts in the attic this time and saw no problems.
After some Googling, I found the youtube video noted below.
I attached my shopvac to the outside drain pipe and vacuumed out the pipe.
It ended up clearing a couple of clogs and a few cups worth of water.
The problem was fixed immediately and has not happened again.
Two pages that helped me...
http://frugaldad.com/2008/05/20/diy-project-2-unclogging-an-air-conditioner-drain/
http://www.youtube.com/watch?v=HyvPR7yMqbk&feature=related (How to clean your clogged ac condensate drain line diyvac.com)
Posted on Aug 12, 2012
The owner's manual indicates that some models will display the - AC message when operating on the backup batteries. I would check to see that there is 24-volt power to the thermostat.
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I had the same problem and the funace was switched off.......now it works fine.
Posted on Jan 08, 2009
"Possibly" the controller to the T-Stat is shut off. We just had that problem but we had rented the basement and we think the tenant shut off the unit over night.
Posted on Aug 17, 2008
Exactly same problem .. the -AC ..
Posted on Dec 08, 2008
The owner's manual indicates that some models will display the - AC message when operating on the backup batteries. I would check to see that there is 24-volt power to the thermostat.
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i have a honeywell chronotherm III which is no longer working.
i get a HOLD -AC indicator where the temperature (i.e. 70 and heat would normally appear). there is no air (hot or cold) coming out. we've changed the battery as well. not sure what's wrong - but our others work fine.
My system is turned off at the thermostat but as I walked by I noticed that next to the date and time is a long dash (-) followed by AC. If I turn the system on cool, the fan motor never starts up and the dash and AC still stay there. It is going to get hot here soon. Please say this is a thermostat problem!
MaryJo Washington DC
We just fixed our Chronotherm III AC code problem. We had serviced the furnace air filter and replaced the cover a little off. After checking the fuse switches and cleaning all connections, we reseated the furnace door covers. Blessed heat!
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