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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 7582
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Carrier thermostat problem

Customer Question

carrier thermostat problem
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
The thermostat display is blank....model 33CS420-01......no storms, no power outage....
Expert:  Phil replied 1 year ago.
Hello,So far it sounds like the furnace is unplugged or the breaker to it is off. OR the 24 volt transformer inside the furnace has burned out, OR a fuse has blown in the 24 volt circuit. Tell me a lot about your technical skills sets and if you have a multi meter or not, we can go from there..
Customer: replied 1 year ago.
Thanks.I reset the breakers and nothing.......about 15 minutes later the thermostat had a display and it was working again. I would assume resetting the breaker would instantly provide power to the thermostat. It's working....just don't want to go thru this againJim
Expert:  Phil replied 1 year ago.
Hello again Jim,
It is an electronics bug, the problem will very likely recur, we do not know where the bug is yet however.
Next time it happens, if there are batteries in your thermostat, remove the batteries and put them in backwards for 5 minutes, then take them out and put new ones in the correct way.
With intermittent problems its a waiting game, you learn a little more each time it happens so that you know which printed circuit card is acting up.
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Customer: replied 1 year ago.
I have no idea if this thermostat has batteries. I have not figured out how or if it opens
Expert:  Phil replied 1 year ago.
You can use a knife to pry the front portion off of the much thinner wall mount plate behind it.
Start on one side and work your way around. Once you get the front off, replace any batteries you find inside.
.......
We are on the honor system here. Please remember to rate my service before you leave today. It is how I earn a living, and does not increase your charges. If you need anything else, just let me know. You can continue asking follow-up questions at no additional cost.
.
Customer: replied 1 year ago.
Any idea if this model has batteries?
Expert:  Phil replied 1 year ago.
Hello again,
Batteries are not required, that is unusual for such a complex thermostat
http://screencast.com/t/ouKlSoFQla
This leaves us with an intermittent anomaly with the electronics in the thermostat or at the printed circuit board as mentioned earlier. Let me know a lot about your skill sets and I can coach you some testing, you will need a multi meter.
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Here are some programming manuals in case you need them later.
http://dms.hvacpartners.com/docs/1005/public/0c/88-505.pdf
http://www.kjs-properties.com/thermostat2_owners.pdf
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Customer: replied 1 year ago.
Thanks...... Sounds like my best bet is to replace the thermostat
Expert:  Phil replied 1 year ago.
Hello again, there is only a 50% chance that the thermostat is the problem, the other 50% is that the printed circuit card in the furnace blower compartment is the problem.
We cannot find out which until it fails again, the hope that it stays failed while we do a few tests... that of course is problematical. Intermittent problems are like that.
The problem with changing parts, regardless of what the sales man says or the box says 'easy replacement fits all systems' the huge installation manual tends to be-lie that.
If you do change the thermostat get the very same exact model then change it wire for wire, one wire at a time with the furnace unplugged...then it must be programmed per the 85 pages of instructions.
I would be inclined to wait and see what develops.
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We are on the honor system here. Please remember to rate my service before you leave today. It is how I earn a living, and does not increase your charges. If you need anything else, just let me know. You can continue asking follow-up questions at no additional cost.

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