How to further diagnose the central air conditioning compressor fan motor and capacitor

air-conditioningrepair

I have a 15 year old Bryant Central Air unit in my house. Yesterday it stopped working. Here is what I have checked.

  1. The breaker in the basement is not tripped.
  2. The furnace works fine from the thermostat.
  3. The blower downstairs by the furnace runs when AC is on and blows room temp air into the house, but the fan on the compressor is not spinning. The fan on the compressor does spin freely when I manually spin it with a stick.
  4. Checked for fuses in the outside box. There are no fuses outside, only an on/off pull thingy with two metal plates that you have to turn upside down to turn off.
  5. The capacitor is not flat on top, but far less rounded then any of the examples of blown AC dual capacitors I've seen on youtube.
  6. I get 220v in on the contactor.
  7. I get 220v out on the contactor.
  8. I get 24v from the thermostat.
  9. When the air is on at the thermostat the contactor solenoid is in, when the air is off it is out.
  10. When the air is on at the thermostat I hear a buzz coming from the outside compressor but I can't tell what the source of the buzz is.
  11. If I push the solenoid in when the AC is off, the compressor does not start up and the fan does not spin, I just hear the buzz.
  12. If I wait by the compressor outside for a few seconds while the AC is on there's another buzz sound that goes off for about 3 seconds then stops. From listening to the AC when it was working this is the buzz sound that goes off before the compressor and fan usually kick in.
  13. After leaving the non-functioning unit on for a few minutes while I diagnosed I noticed that the metal on top of the compressor fan motor was VERY hot to the touch. It cooled after I turned the AC off.

I'm thinking the fan motor on the compressor is dead or the capacitor is bad. Is there a way to check the capacitor and the fan motor while they're still in the unit? With the power off of course. Does anyone think it's something else? Do I have to buy the overpriced ($485 for the manufacturer fan motor and $200 for the dual capacitor) replacement part from the manufacturer or can I use a third party manufacturer? Any other help would be appreciated. As much as I'd love to bring an HVAC guy in here I just can't afford it. Either I go without AC, or I fix it myself.

EDIT: With the AC on I manually spun up the fan on the compressor and the fan started spinning and the AC unit fired up.

Best Answer

I ended up pulling the capacitor and testing it with my ohm meter. It was dead. I could have easily gone to the local HVAC supply, purchased a new capacitor for $30 and installed it myself. But, because I also wanted to have the pressure tested, I called in the guy who installed my furnace. He affirmed that I "did good", it was the capacitor. And because I had done most of the diagnostic work, he cut me a good deal.

In the end, the most important bit, on a 95 degree day when the humidity is 70%, a happy wife is a blissful life. ;)

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