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A few weeks ago, I noticed my HVAC was blowing hot air. I looked outside and my condenser fan was not spinning. With a push from a stick, it started and and was back to normal. Over the next couple days, the same thing happened (intermittently), but a stick wouldn't solve. I had a backup brand new dual run capacitor so I installed. The old capacitor btw tested above spec, but had rusty terminals, so I figured that could have been the problem.

Well, after working perfectly fine for a few weeks after the install and thinking all was fine, the fan was not spinning again yesterday. When this occurs, the unit buzzes and gets hot as if it wants to turn on the fan. Any thoughts on the possible culprit? If it's the fan motor, is that a part that can be sourced/replaced easily? The system was installed in 2011 and has never had this issue in the 7 years I've been using it. I've included a pic of the schematic and top of unit (Thermal Zone).

Voltage tested fine on the load side, and fan motor also tested fine with a resistance test. Eventually, the motor started making a whirring/scraping noise and then stopped for good, so it seems there was a problem mechanically with bearing(s) perhaps. In any event, unfortunately a local motor shop could not supply a compatible unit, so I bought online. Installed and working fine so far. Also replaced the contactor relay as it was rusty (and cheap). Thanks

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  • What gets hot, exactly.
    – JACK
    Jul 9, 2022 at 16:10
  • I was referring to lots of heat coming from top of unit, as if compressor was running.
    – David L
    Jul 9, 2022 at 17:15
  • A motors that doesn't start until poked would seem to indicate a bad capacitor, but you already tried replacing it. Jul 9, 2022 at 17:22
  • The diagram shows an optional start capacitor as well as the run capacitor. I guess your unit doesn't have one? Jul 9, 2022 at 17:24
  • No, I'm fairly certain I don't have the optional start capacitor as the associated wires are not connected to the run capacitor
    – David L
    Jul 9, 2022 at 19:52

1 Answer 1

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Buzzing usually indicates a problem with the contactor / relay. Check the voltages on the load side while buzzing. Make sure the contacts are clean. Disconnect the compressor wires and manually hit the contactor to see if the motor starts. It should if the motor and contactor are good.

The fan motor can be replaced. I'd avoid, like the plague, getting any motors online. If you remove the motor, take it to a local motor repair shop. They'll have the ability to test it right there and you'll know if it's bad. They will also be able to get you the right replacement and give a warranty.

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  • I have to agree with just about everything JACK said. I'll just add and say that since the OP had replaced the capacitors it's almost certainly the motor, contactors don't fail often, they are pretty robust, but it's a possibility. Hopefully the OP will diagnose it by taking various voltage, current readings and not just "throw parts at it". Jul 9, 2022 at 16:46
  • @GeorgeAnderson You're right, they don't fail often but they can get pitted or dirty. My AC would go out every few years because of ants blocking the contacts.
    – JACK
    Jul 9, 2022 at 17:04
  • Thanks guys. It's working fine at the moment, so I'll have to wait to fully test. What voltage on load side when buzzing would help diagnose? For now, I switched one of the load wires to a terminal that wasn't rusty (the others looked fine). Can you explain the comment about "manually hitting the contactor"?
    – David L
    Jul 9, 2022 at 21:25
  • @DavidL The contactor is normally controlled by energizing it's coil from the thermostat. You can manually do it by lifting up or pushing down on the movable contact bar so you can momentarily operate it from the condenser. Just be careful what you're touching. You should be looking at 120V phase to ground and 240V phase to phase.
    – JACK
    Jul 9, 2022 at 22:21
  • @JACK Thanks. Ok, just depressing the bar, sure. Thought you meant tapping it somehow. Mine has a bug cover, but can remove to access. I have three load wires from contactor, two go to compresssor, common (shunted) and run connections, which I could disconnect. The third load wire goes to common on capacitor, and then to fan. Sounds like I would only leave the third wire connected for the pushdown test.
    – David L
    Jul 9, 2022 at 22:34

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