What makes our thermostat click on and off continuously?

We have a 100 year old house. We had a new electric heating/cooling unit installed in the attic for our upstairs 4 years ago, and downstairs has the original gas furnace.

We have had several problems, seems I call the repairman every year for something. Our thermostat keeps clicking on and off, like doesn't even run a second and shuts off, clicks on again over and over. We just turned it off, and dh bougt a new thermostat and changed the air filter. Was fine for a while and then started up again. We've called the repairman for this in the past but I don't remember what they did/said. We've had three different thermostats now, don't think that's the problem??
What makes our thermostat click on and off continuously?
It sounds as if the fan kicks on and off quickly for no reason. There are two possibilites for this:



1. An intermittent short in the wire between red and green. This can be a real hassle to track down. Ohm out the wiring and check.



2. A fault in the printed circut board that runs the fan. On many of these relays are normally closed. This means that they have to power up to keep the fan off. If the board has a micro crack in it, when cold the fan will on and off for just a second or two. After the unit is warm, it won't do it anymore. It can be maddening because it usually happens at night or in the early morning.



Hope this helps.



Former lead tech in a very large HVAC firm.
What makes our thermostat click on and off continuously?
Are there air currents or drafts hitting the thermostat to freak it out? LOL :)
your temp in the house Drops Below the set degree in your House thats why it Keeps Coming On
You obviously have a draft or a cold air leak near your thermostat . A thermostat regulates the temperature,and when you set the thermostat at 68 for example,if the air around the thermostat gets cold it will click on again.

I would check for any open cold drafts in the house and insulate it good for the upcoming winter .
I had same problem,even if you clean your filter

every week, there is still dirt built up in motor

the repair guy, said they need to be cleaned once a year.there could also be a short in the compressor. I am sorry but looks like you call repair man again. good luck
Change the location of the thermostat with the aid of a specialist.