Compressor fan stopped

[jdc0222]

Hello. Hoping I can get some feedback before calling someone or tearing into my A/C unit myself.

(I am not sure what to call it, so I will call it the compressor fan. This is the fan on the oustide of the house that cools the compressor. The fan inside the house that circulate air works just fine, although now it circulates HOT air!)

My A/C stopped working last night. I can move air around the house, but it's warm air, and getting warmer. I turned off the entire A/C system to give it a rest. This morning, I turned it back on and checked the outside components where the compressor is. The compressor fan is not spinning. I can hear the compressor working, but the fan is not moving. I assume that if I don't cool off the compressor, I am not going to be able to cool off the air. Right now, I turned everything off until I can research what to do about the fan.

Everything is really old, definitely more than 20 years. I had the A/C checked up back in May. Topped off the freon, but other than that, the guy said everything looked pretty good, except for being old.

Thanks for any feedback.
Jon

[HayZee518]

check first things first. outside by the condensing unit, there should be a disconnect. check that the breakers are on, if one has tripped, reset it and turn it back on. The "condenser fan" thats what the unit is called, turns on by way of the thermostat and a fan control relay. it operates off a 24 volt control transformer. check the fuse of the control transformer.

[jdc0222]

Thanks.

I checked the disconnect. There are 2 fuses inside, no circuits to reset. I will shut the power off, then pull out the fuses and look to see if either are blown.

Since the compressor is turning on, what is the chance that one fuse is for the fan, the other for the compressor? Wouldn't the compressor unit require both fuses to give it the full 240 volts?

The control transformer is inside the compressor unit, correct? Or should I be looking someplace else, inside the house somewhere?

Thanks again,
Jon

[HayZee518]

ok, yeah 240 for the compressor and condenser fan. so if the compressor is running, chances are good that the fan contactor is receiving power on the LINE side. Next you'll have to find out when the fan relay is supposed to turn on. Look to the schematic for what is connected to the fan relay coil. some device, a relay contact, a temperature device etc. since the control circuit is 24 volts, you can use the meter to find out what isn't feeding power to the fan relay coil. in a ladder diagram the whole chain on the right side is common 24 volts unless it is marked different. on the left side is the HOT 24 volts. going horizontally will be the devices connected in series to the fan relay coil. go from the hot to "neutral 24 volts" and read what the meter says. leave the neutral probe there and jump to the next device wire and see what it reads. keep this up until you find what is open or doesn't read a voltage on the way out. this my friend is your culprit.

[jdc0222]

Well, I looked but didn't touch. From what I can tell, there is a relay and a condensor. Condensor appears to be dual, running both the compressor and the fan. I'm not sure if the condensor could only "half fail" on the fan side or, or if it must be OK since the compressor seems to work fine. Also, it looks like the fan is wired off of the condensor, so I don't know how to tell if the relay is the cause.

Unfortunately, the wiring diagram is almost illegible due to age.

Other obersvations:
The fan turns freely if I spin it, so I think the fan motor is ok.
I turned the A/C on and the compressor ran for about 10 minutes and cut off. I'm assuming it overheated and automatically cut off.

Probably time to call in a pro... any ideas what to expect to pay for a repair to one of these electrical components? Seems straightforward, maybe an hour of professional time and the part?

Jon

[HayZee518]

a start/run capacitor is a dual capacitor. if a motor uses one of these it is for this motor only. companies don't use wires from a capacitor in one location to feed a motor in another location. the problem is in the condenser fan relay or the motor itself. a replacement motor could run as much as $150 - a typical service call is about $125.