I have a Bryant heating and air system. The digital thermostat will not come on--it is blank. I have checked breakers. Power is coming into the indoor and outdoor unit. I understand there is no reset and I checked the fuse in the indoor unit. How do I check thermostat? Any suggestions appreciated.

 

pull the thermostat off of the wall leaving the base with the wiring if possible, if it is a nonbattery powered thermostat you will read 24 volts from the red terminal R to the common terminal C. if so then the thermostat is more than likely shot. if this is the case and you dont have another thermostat then you can jump the red wire to the yellow wire to bring on the ac temporarily but obviously it will not turn off until you pull the jumper wire

 

Does your thermo. have a battery in it? Need replacing? I have an older termo that has a AA batt. in it.
Just a thought.

 

The couple times I've seen a blank thermostat is because someone accidently (or purposely in the case of kids) turned the switch off at the furnace). Might want to check that. I know you already said you have power coming in to the unit, but I thought I'd throw the suggestion out anyway. If the unit is working and you just can't see anything on the thermostat, seems like the thermostat LCD screen is just bad.

 

I checked r terminal to c terminal-no voltage. I tried using a jumper from red to yellow--nothing happened. I was told to check inside unit transformer. It has 240 in, but have not checked voltage out. Should I check this next? Too hot in attic to check now.

 

yes, check the power coming off of the transformer, you should have 24 volts on the secondary side, just be careful slidin your hands in that tight electrical compartment. most newer airhandlers have fused transformers or an actual low voltage breaker on the transformer itself so check for one of those as well, just trace off the transformer to the terminal strip inside the airhandler

 

I replaced transformer because it did not have any coming out. I now have 29 volts coming out and it got very hot. Thanks for any help.

 

Just experienced this problem and did the voltage checks and confirmed ckt brkr was good. Going into the 'box' and checking for transformers, etc. is a little more than my meager talents support. BUT, what I didn't think about (nor did I know to think about) the float switch on my air handler shuts off power to the thermostat. I learned an $84 lesson today (ouch) - check to make sure the line for the float switch hasn't been bumped and declined. Float switch worked as advertised albeit helped by gravity. Righted line/drained water and voila - power back to thermostat and a/c working after about 5 minutes auto system reset.

 

Thanks BryWilliams. You saved me big time. I changed the air filter today and must have bumped the water detecting float. It killed power to the thermostat and I almost called a heating and air guy because I didn't find anything wrong with the fuse box. Luckily I ran across this thread and your answer!

Thanks again.

 

Glad you found a helpful thread and that your problem was a minor one. This thread will remain in the archives for reading only. If you have a further question... start a new thread.