Hi,
We have a airconditioner from Carrier. 3 days ago, there was a loud noise outside our house, We thought that as it was raining heavily, it must be the thunder or lightening. 2 days later, we noticed that our thermostat is not working. Now we are not sure if the noise we heard was something to do with the airconditioner unit outside the house or what.

All that we know now is, it is dead. We switched the trip switch to off and then again switched it on and so also opened the fuse outside the house by the a/c unit and checked it. We could not make out anything. We have not yet checked the unit in the attic. We are not sure what we need to do there.

We are guessing if it is the thermostat that is the culprit. It is 10 years old. It does not have batteries. Do you all think the thermostat is dead and hence it is not sending signals to the a/c to start when the room is getting warmer. Can you please help us through this? Thank you all so much in advance.

First you need to take your electric test meter and check for 240 volt power at the contactor in the outside unit and or check the fuses or circuit breakers to be sure they are OK. When that is all done report back with your findings.

Sounds to me like your 24 volt side that controls system is not working.. maybe either your transofrmer is dead or if you have a 3 or 5 amp fuse in system it is poped. Either one of these would be in the airhandler.