I just bought and installed a NOMA 7 day programmable thermostat, part number 52-2549-0. It runs both the heating and air conditioning. Everything is OK but the ac stop every 3 minutes for a couple of minutes then it resumes again !
I set the temp 5 degrees C less, but the problem is the same.

With my old manual thermostat, the ac runs until reaching the desired degree (some hours of continuous running)

Please help
Thanks

Does it always do that? If so remove the cover to the thermostat, remove the red, green and yellow wires, twist them together, if the system stays running it's a thermostat problem, if it doesn't it's something else, possibly a freon issue. Post back and let us know what you find.

I twist the wires together and the system runs and stops every 2 or 3 minutes (cycle) like before... So I thing that the thermostat is OK and the problem is elsewhere...

What do you mean by freon issue? How can I solve it?

Thanks again.

Some air conditioners have low and high pressure switches, it may be cycling off and on,on low pressure, this could mean it's low on freon. What is the brand and model number on the unit? Does the fan and compressor run?

I just had this same problem repaired (today!) so thought I would let you know what we found.

A circuit board in the air handler needed to be replaced. Wiring was all fine, just a bad board. It was only 4 years old, and no longer covered under warranty. We paid about $400 for parts and labor, but the system works great now.