WE have a zoned hvac system and we are having problems with the master ( first floor ) themostat. It is a Honeywell Trolatemp and it appears that the air conditioning is not shutting down in accordance with the tempature that we have set. It just keeps getting colder and colder until we turn the thermostat to the off position.

Can we just replace the thermostat with the same model, wire it the same way? Is there any other programming to be done and will it affect the upstairs thermostat which is working fine?

Thanks for your help

You might have a defective trol-a temp relay in the circuit. Usually the thermostats do not go bad but it is a possibility.

Is this your system?

http://customer.honeywell.com/techlit/pdf/69-0000s/69-1361.pdf

OR

http://customer.honeywell.com/techlit/pdf/68-0000s/68-0224.pdfOR

http://customer.honeywell.com/techlit/pdf/68-0000s/68-0223.pdf