Thermostat WTHell

[Z_Fan]

Basically just looking for ideas from those with experience as to why my A/C does not shut off automatically when it reaches the target temp...?

So my thermostat has 4 wires going to it.

When I put the house on heat, it heats up house temperature and then stops when it gets to the target temp.

When I put the house on cool, the A/C comes on and does not shut off - ever - until you manually turn it off at the thermostat. It used to work, and now it just keeps going past the target temp.

I am reasonably sure the thermostat was removed, then replaced, and possibly hooked up wrong at some point. A brand new thermostat was hooked up, and it does the same thing.

So I'm wondering if it is likely wires got mixed up at some point and are being attached incorrectly - or if there is some other source of the signal for the cooling temperature that isn't getting sent - ...

Thoughts/suggestions?

[Darell_n]

How old is your a/c and furnace? It could be the board on your furnace is pooched.

[Crazyjoker77]

its real easy to check if the furnace is wired up correctly. Pull off the electrical inspection cover. Inside you will see a board. On one side of it you will see a terminal strip with a bunch of small gauge wires attached.

Terminals will be marked as follows
R (24v off transformer)
W (call for heat)
G (Fan On)
Y (Call for cool) (may not be hooked up in the furnace but will be on the thermostat)
O ("neutral that goes out to your condensing unit)

Just write down the colour or wires in respect to where they go and compare to the thermostat, It will have the same markings (except O)

Although mixing up any of those don't really seem like it would cause your issue.

IF the thermostat is still using a mercury switch it being level on the wall is very important and will cause your issue though.

When boards go they usually get stuck in one mode, it sounds like your can get ac to stop if you slide it over to heat or off. Id really be looking at the thermostat. which can be tested very easily with a multimeter.

[sillysod]

You can also eliminate the t-stat all together and jump the terminals on your furnace board.

This will allow you to determine if the problem is pre- or post- thermostat.

For some reason I had to throw the breaker off on my a/c and furnace as well as pull the battery in my t-stat yesterday because my a/c wouldn't kick in.

Had to do the same thing last year. Been cycling on/off perfectly fine since.

[Z_Fan]

The furnace is about 15 years old.

Thanks for the suggestions - there may be something wrong with the board. In the winter it had a little problem too, where the furnace would cycle on then it would work for a few minutes, and then "click click" and turn itself off and then it would basically rinse and repeat this...

So perhaps that lends itself to the board starting to go.

I did have someone look at this, and it seems to me that after that it worked for a while as far as the heating goes.

The breaker on the A/C has been reset. I will try turning the furnace off at the switch, shutting the breaker off, then back on, then turn the furnace power back on. Not sure this will matter, but will try anyhow...see what happens.

I'll check out the wiring too. Thank you all for your input...