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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Mu Honeywell thermostat has gone blank. It comes back every

Customer Question

mu Honeywell thermostat has gone blank. It comes back every so often then goes blank again. It controls air and heat, all electric. I do not see a battery in the unit. Number on the tag inside read T8400C 1099(2). First time home owner, clueless about this
Submitted: 1 year ago.
Category: HVAC
Expert:  Heath.M replied 1 year ago.

Hello my name is ***** ***** will be my pleasure to assist you. You will need to take the thermostat cover off the wall plate when the thermostat goes blank and use an electric meter from the R terminal to the C terminal to verify that there is power to the thermostat if there is then the thermostat is bad if there is not you have an issue with the transformer in the airhandling unit of your system.

Customer: replied 1 year ago.
As I stated I was clueless about this and do not know what an R or C terminal is. As it ends up I had an HVAC company come out and had a whole new system installed. Thank you for taking the time
Expert:  Heath.M replied 1 year ago.

you are very welcome.