Air Conditioning - thermostat/AC problems

I just baught a home and im having problems with the thermostat. It seems to work properly in the heat mode.....but not in the AC mode............I have done several things already. Like changing the thermostat three times..........I ran new thermostat wire:wall: . This is a central AC unit......If someone has a wiring diagram and or suggestions.........please don't be bashful.......thanks...jo....:wall:

Are you certain that it's the thermostat? Did you check the A/C breakers in the breaker box and the disconnect on the outside of the house near the central unit?

Maybe if you started with telling us what it does or doesn't do, specifically.

Does the inside fan/blower come on when you turn the thermostat so the a/c will turn on?

Does anything happen?

Nap and Goldstar thanks for your feedback...........to answer your questions yes the unit does run , but only when I flip the main breaker. Then it will run constant. I replaced the two shot gun shell type fuses located @ the AC unit......and I spliced a broken wire at the same time. Then I ran new thermostat wiring at the same time I replaced the thermostat. Yes the AC works great.........it doesn't take long at all to cool the place down. The problem is......it won't shut down or cycle the way it suppose to....../any more input will be great thank you...jo

Does the indoor unit cut off when you turn off the t-stat but the outdoor unit continues running? If so you probably have a stuck contactor.

I'm with Tiger. It sounds like a stuck contactor inside the outdoor unit.

Does the indoor unit cut off when you turn off the t-stat but the outdoor unit continues running? If so you probably have a stuck contactor. Tiger please let me start over from the begining........im not very good at explaining things like this Via my key board. perhaps I should have asked the question. Does a T-stat that serves a dual role ie heat/cool have seperate wiring going from the T-stat to the furnace. Because this one had only two wires going from the T-stat to the furnace when i baught the place. The only way i've ever been able to use the AC part of the system, is to flip the main breaker in the breaker box. Then the unit will of course run all the time. So my question should have been......Does anyone out there know exactly how the wiring must go from the T-stat to the junction box located at the furnace.......I have no idea how the previous owners managed to operate this......unless they let it run constant..........and that I do not want to do. Thanks for your time.....jo

You should have 4 or 5 conductor wiring from the t-stat to the furnace. From there you usually have 2 conductors to the condensor. This is assuming unit is not a heat pump.

Is it an older home that had a/c added on?

You should have at least a two conductor low voltage set of wires that go out to your comdensor from the airhandler, "they will look like t-stat wires". Take the panel off of the airhandler and tell us where they are landed.

Like Tiger says you sould have at the least 4 wires in your stat and a cool option on it.

Sounds like you are going to have to run a new set of stat wires to your stat and maybe get a heat/cool stat if your is not compatible.

Also a good chance that they may have jumped the contactor to get the unit to run non-stop.

The unit i'd guess is about 20 yrs old......No its not a heat pump or swamp cooler........I have a furnace inside the home and a AC unit that sits on a concrete slab outside. Does anyone know how I can get my hands on a wiring diagram for this system...I'd like to thank both of you for all your feedback thus far...jo

Check and see what you have for 24V power to the stat. if the furnace ran for you on two wires and the AC runs when you turn the breaker on. It should have its own transformer. If so pull the R to RC jumper in the stat.

ED;)

Not being too bright on HVAC, I'm going out on a limb here. Is there a second thermostat somewhere in the house? Does the furnace have a summer/winter switch on or near it?

Not being too bright on HVAC, I'm going out on a limb here. Is there a second thermostat somewhere in the house? Does the furnace have a summer/winter switch on or near it?

goldstar..no theirs only one T-stat and it doesn't have a summer/winter change over switch option. But I think at this point if I had a wiring diagram Id wire in a seporate T-atat for the AC side of the system. But no one seems to have a diagram and I don't know enought about it to just wing it. But thanks to all who have sent their advice....jo

If you go to a AC stat dont forget you need a 24 V transformer there.
You say the AC ran how did you close the 24v wires???

ED;)

If you go to a AC stat dont forget you need a 24 V transformer there.
You say the AC ran how did you close the 24v wires???

ED;)
I didn't....it must have been the other owners b4 me who did