The fan on my central A/C keeps running despite the thermostat being "Off"...?

Question

Recently, I had my Central A/C system inspected and everything checked out fine. However, lately, I've been noticing that the fan kicks on intermittently, even though the thermostat is "off" for both. I have a digital thermostat running my house, where you have to press a "Program" button through the cycle until the display shows "Off" on the screen. Any suggestions, and would I need a new thermostat?

Answer 1

So of the programmable thermostats have a built in feature called programmable fan. This turns on the fan on a set schedule to promote better indoor air quality. The other thing that it could be is the temperature switch on your furnace. In older units it turns on the fan at a set temp and it may be doing so. For more info, see the thermostat page at www.hvac-for-beginners.com

Answer 2

First - make sure your fan isn't set to some kind of delay - (sounds like you've done this but double check) Typically your indoor fan runs on a delay with the rest of the unit - meaning....that before your entire unit kicks on your indoor fan will start in order to boil of some refrigerant in your evap coil so you don't slug your compressor with liquid refrigerant. Although in this case the fan should eventually shut off once the entire unit has been running and shuts off



Next I would pop the sub-base off from your t-stat....check to see if the copper from the red ( hot wire ) is coming into contact with the green ( fan wire )...note could get shocked if power is on if you touch the copper.....if this is so then your power coming into your t-stat ...by-passing your fan switch causing the fan to continually recieve power.



lastly I would check the fan relay ( this is in the unit ) might want a technician at this point ) but if you do it - PULL OUT THE DISCONNECT ( the main fuse going into the unit ) then follow your wires that come from your indoor fan to where all the electrical housing is....the wires should run to a capacitor ( a little silver looking like can typically) and then to a relay ( so thats the relay so u know..or just look at the pictoral diagram will help u out.....good guess this might be your problem.....pull it out ( Make Sure power is off ) remember which wires went to which...go to a supply house - should be good from here on......or just have a tech come out and pay 100- 200 bucks......relays are pretty reasonable to buy.....however if its a newer unit it might not have a relay and everything may be wired in the board and your getting some kinda short.

Answer 3

If it's a wireless electronic thermostat, the fan could be starting from "interference" from an outside source.

I have a wireless door chime that rang intermittantly and drove me crazy until I read the instructions and had to change the signal.



Hey, it's a thought!

Answer 4

With as little assistance given i'd suspect its both 24 volt feedback going to the blower motor wiring. yet maximum in all probability its the blower motor relay that has lengthy gone undesirable. relying on you furnace or air handler gadget you may want to have a relay that would want to get replaced or one it extremely is solder into the administration board and that you'll favor to change the administration board to get the unit operating wisely.

Answer 5

Sounds similar to our thermostat. Ours also has a fan setting. Check to see if your display says "fan".

Answer 6

The fan setting are usually, OFF, ON, or AUTO. If you are sure that you are not set to AUTO or ON, I would suspect a bad stat or loose wire.