The set up: baseboard hw via nat gas, 2 zone - working great for 20 yrs. Central air whole house one zone added 2011, air handler in the attic and compressor/condenser outside at the side of the house - working great from day one. Switch t-stat from cool to heat back in Sept/Oct and everything has been working normal for months. Wake up New Years Day and the outdoor compressor/condenser is on, not the air handler. I check the t-stat to see if my wife switched the t-stat setting and it's on heat as it should be. Completely shut off the t-stat and outdoor unit is still running. Only way to turn off outdoor unit is pull the outdoor shutoff or flip the breaker in my house's panel. Where do I start investigating myself before I call in a pro? Thanks.

 

What type of thermostat controls the cooling? Try disconnecting the Y wire there to see if it shuts down the compressor.

 

Two transformers to one thermostat. Possible bad thermostat now.

 

Vision Pro 8000. I'll swap out t-stat this week and see. Thanks!

 

If you have two red wires..... Rh and Rc..... make sure they are kept separate and installed in the right location.

 

Step 1, installed new stat...changed nothing.
Step 2, pulled Y wire...changed nothing.
What's next?

installer said it sounds like a mouse in the wall chewed something - in all my remodeling I have never seen evidence of any rodent so I'm thinking something outside is causing the trouble. I investigated the attic and everything looks normal, like it has from day 1, now mouse remnants.

 

The Y wire from the thermostat and a C from the air handler go to the outside unit.
I would next disconnect the wires at the outside unit to verify that it is a wiring issue. Otherwise possible stuck contactor in outside unit. If not then check the wires at the air handler. Then check wiring inch by inch.

 

First off the LED blinker was blinking 8 times, tag says contactor or wiring. Ok here is my next step...with outdoor shutoff key (?) removed i removed 24v wires from contactor, plugged in shut off back in and compressor and fan blades turned on. Pulled shutoff key out. Plugged 24v wires back in. Went to the attic and pulled cover off air handler and everything looked good. Followed wires thru all the insulation and everything is intact, no chewing and no jacket tears.
Not sure this deduces anything but y next step: I put shutoff key back in (compressor turned on) switched stat to cool, set to 63 and air handler came on and compressor shut off. Brought stat up above house temp and after stat 'clicked' air handler ran after the fact like usual and shut off, compressor still off. Does this satisfy that the stat wires are fine and it's a contact problem?

 

Guess I'll just replace the contactor when the weather warms a bit.

 

Well I'm back at this with warm weather looming . I replaced the contactor and the capacitor, I get the same issue.

 

Please review my ongoing issue.


Moderator note: Threads combined and moved to A/C forum.

 

You'll need to refresh us where you're at but something is standing out here......

This is saying that the contactor could be stuck in.
Now you've changed the contactor and still have the same problem ?
The compressor and fan are running with the contactor out..... correct ?
If this is correct..... you're going to need a test VOM.... ohmmeter to check for shorts in windings.

 

What is the model number of the outdoor unit? Pictures and wiring diagram would help.

You said a/c but if heat pump (or high end system) it might have a defrost control board which has its own relay that could stick.

 

Right, the compressor ran with and without the 24v wires attached to the contactor but the unit did shut off in Jan when it switched the t-stat on/off. After I replaced the contactor he other day I restored all the power with the t-stat not calling for COOL and the compressor ran. This time when I turned the t-stat on/off it didn't trigger the compressor off. Also out of not knowing what else to do I replaced the capacitor.

is there is something inline before the contactor causing this to want to constantly receive power? Could my disconnect be faulty?

I'll check in the morning, but it's a Heil, I think C4A336. Not heat pump.

ok at 3AM I decided to play more. Compressor was off at the basement breaker, turned t-stat to cool and 64, went to the basement and flipped breaker to power the compressor and it kicked on. It ran for 2-3 mins and tripped the breaker and shut of (of course). Reminder back in Jan we lost power and when it came back on this thing just started running for no reason, could the power loss been a surge that mucked it up?

 

Is this yours? http://www.yorktechsupply.com/downlo..._ICP_25580.pdf page 4/5 for wiring diagram.

You disconnected the 24vac (Y and C) at the the contactor and it still runs? Stuck contactor, mis-wired, or shorted/pinched wiring (crankcase heater).

 

When you replaced the contractor you may have installed the power from disconnect to the load side of the contractor.

 

A stuff, yes that's mine.

It's been wired right and running right since 2011. When I installed the new contactor and capacitor I replaced one connection at a time. I doubt it's wiring since it's acting the same way it did in Jan when this problem happened.

Something happened when power was restored New Years morning.

 

Your description is indicating a shorted motor winding..... possibly in the compressor. The diagram shows you have a single pole contactor. That means only half the power (leg) of 240v power is shut off. A shorted winding to ground will use that 120v power to run. When the system is powered it will run for a minute or two or trip the breaker.

The point you are at now is that the wiring to the fan and to the compressor needs to be disconnected (and carefully labeled) and then checked for shorts/leakage to ground.

 

Ok, beyond my comfortibility...time to call for service. I'll report back when I find anything out. Thanks everyone.

 

My nephew came over and deduced it was a faulty crankcase heater. He said something like it shorted and supplying power that made sense at the time. He disconnected it and I have a/c again. Anyone know what part number I need to order a new one? The parts list pic says item #35, but no 35 is listed in the chart.