AC Compresser runs, blows cold air, but cooling fan keeps shutting off?

Question

We have an older Carrier A/C unit approx 15 years old. Carrier website has no information on it.

The compresser appears to work- will start to cool down house a bit, but the cooling fan starts to work (about 5-10 minutes) then shuts off, and the unit starts to heat up, so obviously we turn the unit off.

Any ideas as to what this may be? We called a guy in and he basically said it could be anything. We're looking right now at capacitor or the motor, but don't want to replace one and find out it was perfectly fine. How do you troubleshoot them?

Idiot technician left note that "voltage supplied is not sufficient to turn condensor fan/compresser"

Any help would be fantastic.

Answer 1

Did the service tech measure supplied voltage? Low voltage supplied to the fan would be very unusual. Not likely to be the cap, the fan would not start. The motor replacement is fairly straight forward, call your local HVAC supply house and give them the model number and they will sell you the correct one. Replace the motor cap at the same time you replace the motor - this is best practice.

Answer 2

Does the fan turn freely?

A lot of the older carrier units use an electric motor that needs periodic oiling. If the unit is not oiled, it eventually gets hard to turn. This causes the motor to overheat and quit turning.

I don't think it is the capacitor, when it goes bad, most of the time the fan will not start at all.

Start by trying to oil the motor. If this is the case you will find out quickly and cheaply. Next I would replace the motor, but at the age of this unit, replacement of the entire unit is something you should consider. A new uit should easily pay for itself in electrical savings in less than 24 months.

To oil the motor look for 2 different holes in the motor. There should be one on each end of the motor and should have a short tube that aims straight to the motor shaft. These tubes will be about 1/16 of an inch in diameter. They might have a small cap covering them that is normally yellow and plastic, however it can be any color and can even be a small metal cap.

Answer 3

Since the condensor fan is the first to stop that's most likely your problem.  I'm sure when you touch it it will almost burn your hand.  Replace the motor, a cap is a small price compaired to the motor so get a new one.