Air conditioning repair - semi long

[Robert McGowen]

Any ideas besides calling the AC repairman? I know just enough to get in trouble, but here goes.

The fan on my a/c compressor is not turning on the outdoor unit. I actually have two identical units next to each other, so it is easy to compare a working unit with a non-working unit. (upstairs and downstairs) As best as I can tell, there are only a few parts to the outdoor unit. There is a switch. I blew out the usual fireant carcasses (those in the south know what I mean :() I checked all of the wires and what is supposed to be hot is hot. I pushed in the magnetic switch and got power from both sides, so I think that the switch is good. When I turn on the thermostat, the switch connects like it is supposed to, but there is only a loud hum, no movement. There are also two things which I know from the electrical diagram are a start capacitor and a run capacitor. They each just plug into the wiring with wire blade connectors. I actually replaced one on the other unit before because it was apparent that it was bad as it looked like a soda can that had got too hot and the sides had pushed outwards. There is no indication like that this time, but I have no idea how to test one to see if it is good. I guess that the compressor itself might be bad, but I am hoping for the $50 self-repair and not the new unit replacement option! :D Any idea what to do before spending the big bucks? Thanks in advance. Robert

[Mike Henderson]

The fan motor often fails before other parts of an A/C. If your compressor is running and the fan is not, it's probably a failed fan motor. You can tell if the compressor is running by feeling the output pipe (the pipe that goes into the cooling coil). If it's HOT, the compressor is running. You have to do this test after letting the system cool down. Without the fan, the compressor will overheat and the thermal switch will turn it off. You have maybe five minutes before the thermal switch will cut in if the system is cool before you turn it on.

They can be a bit expensive because they're 220V motors. Maybe someone will post a good source.

The problem I've always had is that I can't wait a week or so to get one shipped to me (because it's too hot) so I pay the big price from the local distributor.

Mike

[Von Bickley]

Any ideas besides calling the AC repairman? I know just enough to get in trouble, but here goes.

Thanks in advance. Robert

You already said it....... Call the repairman.

[Ken Fitzgerald]

Robert,

With power off, can you spin the fan blade? Does it spin easily?

[jerry nazard]

Robert,

With power on, spin the blade (be careful). If the motor runs, then it is the start capacitor.

-Jerry

[Ken Fitzgerald]

Robert,

Jerry's got the right idea. It is possible that the motor has seized up because the bearings have gone bad but typically, that will cause the unit to blow a fuse or trip a circuit breaker. If the fan blade spins easily with the power turned off, as Jerry suggested, I'd try taking something like a thin, small stick and spinning the fan blades with power applied and see if the motor starts up and stays running. If it does, it's the starting capacitor that has gone bad.

[Tom Godley]

like they said above - good advise

I am never lucky with it being the start cap -- mine are always the motor!


The caps can go and not be blown out - and the hum can be from the compressor running.

Just to let you know many of the builder grade models do not have the high and low limits built into them - The compressors can be quickly destroyed when the fan fails without warning. The compressor and lines get HOT

[Randy Denby]

All homeowner a/c compressors in the last 20 years have an internal overload cut-out (klixon). It's basically a bi-metal switch that warps when too hot and breaks the ciruit. If the fan motor is seized or the run capacitor is bad it will cause the compressor to overheat and go off on internal overload. This is very hard on a compressor and if it is weak to begin with, could break a valve throw a rod or seize up. (and short to ground)
Also, quite a few manufactures are going the cheap route :rolleyes: and using a dual run capacitor for the compressor and fan motor. You can tell by it having three terminals instead of two. I have found these to be a common problem ...and it usually has the symptom of fan and compressor not coming on, or pulling locked rotor.
Good luck.

[Greg Cole]

I replaced my fan motor and start capacitor last week. I called every trane service agent in my area last week and nobody woulda been able to come out until today (fan crapped out Monday night). There is an electrical print on the inside of the unit somewhere too.
A capacitance meter or a multi function voltage meter will tell you if the "cap" is bad, if you know how to use either & have access to them (google searching will also tell you how to test the "cap" with either device). If you can't use a meter or don't have one, pick up the phone and call the HVAC man.
The "cap" is usually a 5 micro farad and a couple bucks. The OEM fan motor was $400.00 :eek:.
I wound up with a Dayton motor from Grainger for $65.00 (including same day delivery!).
The relay could be gad as well, but most likely source of the non spinning fan is the "cap" or the motor (or both in my case).

Cheers.
Greg

[Jim O'Dell]

My fan motor just went out a few weeks ago. At our previous house, we replaced it every year for 4 or 5 years straight. Finally got a repairman to give us a pointer. It sat right under the drip rail of the roof. Put a gutter on it and it will make it last longer. I did, and it did. I started replacing it myself...it's not hard. JUST MAKE SURE TO TURN THE POWER OFF!! I got mine from Grainger. Jim.

[Tom Godley]

The high and low limits I am speaking about are the ones on the refrigerant lines - not the overload on the compressor. If the fan fails, the high limit on the lines should stop the unit way before the compressor goes off on overload.

If you look inside many units today you will not find much - sometimes the second tier units are the cheaper units with some of the system protections so they can provide a longer warranty - that should tell you something.

You should never install a unit that will get water run off from a roof - but you see them that way all the time.

You used to be able to spin the fan and if it ran - it would almost always be the cap - unless the motor was over heating.

But from what I understand many of the fan motors today are very small and require the cap to be functioning perfectly - so it may spin and not start and still be the cap.

[Randy Denby]

I apologize Tom, you are absolutely correct. I glanced over your post and I now realize you were talking about high and low pressure cut-outs. Yep, very few come with those anymore. Most heat pumps still have at least a hi pressure cut out,in case the homeowner doesnt change his filter in the winter. I've seen so much "cheapening" of units to save a dollar on pruduction costs it makes me sick. Most all units now come with a single pole contactor, to only break one side of the line , on 220v. This will naturally arc alot when the contacts break...which pits the contacts and drastically shortens the life.Then you have the dual run capacitor "hecho en Mexico" that lasts 1/4 lifetime of the old style, copper drawn thinner,sheetmetal thinner, etc. I'm glad I only have a few more years (I hOpe :) ) in this business