Condenser fan won't shut off
 

This is a strange problem with my home AC...my condenser fan will not stop unless I kill the power to the unit.

I have replaced all of the components (contactor, capacitors, and even the fan motor) in the outside unit except the compressor. I have isolated the unit from the inside electronics by removing the wires from the thermostat to the contactor: no luck. If I take the start and run leads from the compressor out of the circuit, then the fan will stop.

I looked at the compressor connections (at the compressor) and cleaned them off...also no luck.

Am I missing something? Has anyone seen this?

Thanks for any help and ideas you all may have!

Scott

Not knowing what type of setup you have (make/model), I can only speculate on a few scenarios.

= switching relay is stuck
= internal compressor relay is stuck
= bad hi pressure switch

I don't have much experience in HVAC, but it seems like a very basic system. It's a Bryant unit using a Copeland scroll compressor.

The outside unit seems very simple. The only electrical components are the contactor, cap, and motor. The only other component inside the condenser is the compressor.

I have a feeling that the compressor is the problem...

Why didn't I get into the HVAC business ????????

the problem you have is a wiring issue. If the compressor not running but the fan motor is, that means the contactor is open but the fan is still energized. The hot wires to the fan motor are on the hot side of the conotactor. Connect the fan motor to the same side of the contactor as the compressor leads.

If the compressor is running with the fan motor, then the problem is with the contactor. Use a volt meter/multimeter to measure the voltage across the low voltage control wire terminals. If the thermostat is turned off, the voltage should read 0. If it doesn't, you have a low voltage wiring issue. I can help you with that over time. If the voltage is 0 but the contactor is energized, you have the wrong contactor. Replace it with a 2 pole Normally Open contactor.

It is. My DVM reads ~130 volts across the output of the contactor while the one leg of the contactor is open (the other pole is straight through). Compressor is not on, fan is.
If I remove the compressor leads from the contactor output, the fan stops. It seems as if the 130V is coming through the compressor leads! Is it possible that something (electrical) is bad inside the compressor without actually affecting the compression function?

I was worried about that. All of the testing I've done is with the thermostat leads removed from the contactor so I can isolate the outside unit.

Repy to 130V across contactor
 

QUOTE=Scottphys;18897]It is. My DVM reads ~130 volts across the output of the contactor while the one leg of the contactor is open (the other pole is straight through). Compressor is not on, fan is.
If I remove the compressor leads from the contactor output, the fan stops. It seems as if the 130V is coming through the compressor leads! Is it possible that something (electrical) is bad inside the compressor without actually affecting the compression function?

I was worried about that. All of the testing I've done is with the thermostat leads removed from the contactor so I can isolate the outside unit.[/QUOTE]

Is the fan turning at approx 1/2 speed?
What other components if any are connected to the contactor?
Electricaly, if you are measuring V across a single pole contactor with the contacts open, you should get 0V. If you measure across either lead to ground you should get approx 120-130V. Can you attach a picture of the contactor with all wires connected?

Another thought is that if the compressor has a crankcase heater for cold weather, that may be complicating the problem. If it does, disconnect those wires from the contactor and see if that solves the problem.

Change out the contactor and the switching relay. Post back if your still having issues.

Resolution...
 

Thought I'd give a quick reply so maybe I can help someone in the future with this issue.

I had a "pro" come out and look. The compressor blew out one of its three contacts and current is feeding back through to the fan. Also, there is a small refrigerant leak near those connections.

I missed the issue with the connectors when I cleaned them originally. When I pulled the plug from the compressor, one of the leads was attached to the plug, the other two leads were attached to the compressor. I just figured this was the way the connection was "keyed"...what can I say...inexperience with compressors!

I've also noticed some strange behavior that may help someone in the future diagnose a similar problem: the condenser fan will operate normal (fan on when compressor is on, fan off when compressor is off) when no cold air comes out, but when the fan stays on (regardless of compressor), the air is cold. Maybe the start windings in the compressor is connected to the contacts that blew out??

In any case, I want to thank all of you for your help. It's extremely appreciated!