My Honeywell Chronotherm III thermostat is set on heat and it blows hot for a while then the LCD says "HEAT - AC" and it starts to blow cold. Then it goes back to blowing hot then back to cold, etc. the thermostat clicks continuously as this happens. Help

Remove from wall and also remove batteries. Wait 15 minutes to let the capacitors loose there charge. Then replace the batteries with new ones and remount to the wall.

If this does not clear the processor then the thermostat is defective. NOTE that thermostat is no longer available but there are other Honeywells that have taken its place. I have 3 zones in my main house and I have 3 thermostats just like you have but I have had to replace 2 of them over the past 20 years. Lucky for me I had a HVAC shop and stocked a few extras for my home as spares. Good luck.

Thanks I will try it. I replaced the batteries yesterday but did not wait 15 minutes as you suggested. I'll let you know if it works






Remove from wall and also remove batteries. Wait 15 minutes to let the capacitors loose there charge. Then replace the batteries with new ones and remount to the wall.

If this does not clear the processor then the thermostat is defective. NOTE that thermostat is no longer available but there are other Honeywells that have taken its place. I have 3 zones in my main house and I have 3 thermostats just like you have but I have had to replace 2 of them over the past 20 years. Lucky for me I had a HVAC shop and stocked a few extras for my home as spares. Good luck.