My fan on my A/C compressor unit seems to start and even spins up to a reasonable speed, although not quite the speed at which it ought to spin, but then 5 seconds later slows down to a very low speed where you can almost see the individual blades. The run capacitor was clearly blown (the top had mushroomed) so I replaced it. However, that did not solve the problem at all. In fact, the pattern I just described did not change at all.

Should I replace the start capacitor as well? (I'm kind of doubting it since I would guess that a faulty start capacitor would prevent it from starting in the first place.) What else should I try before I call an expert?

Here's the video of what's going on.

  • The compressor and the fan are two different pieces of equipment. You can't see the compressor spinning because it's entirely enclosed. What you're looking at is the fan.
    – brhans
    Jul 15, 2018 at 13:44
  • @brhans I edited my post to reflect this note.
    – Wynne
    Jul 15, 2018 at 18:12
  • I added a video of what's going on: youtube.com/watch?v=egefrF0MMlM
    – Wynne
    Jul 19, 2018 at 22:41

3 Answers 3

  • Have you checked the actual voltages feeding the fan motor ?

    • You should use a volt meter , measure both at the contactor(both in & out sides) and the motor. I would like to know L1 to Neutral , L2 to Neutral and L1 to L2 as there is a slight possibility your actual Circuit Breaker is "broken" on one leg where you might get a reduced connection and thus not enough current passing.

    • Have you cycled your Circuit Breaker Off/On in your service panel ?

      • Your breaker may have partial tripped, only half the breaker tripped and so it has partial connection (brown out voltage basically).
  • Also when you replaced the capacitor was it a dual fan/compressor type ?

  • Or Start/Run type ?

What this looks like is that your fan has a start capacitor and that gets it going but your run capacitor is not working.

Please post your Model number, I know it is a carrier - inside the panel there should also be a wiring diagram - post a good picture of that if you will.


Could also be rusty or poorly lubricated bearings. Try spinning it by hand.


There can be several issues that can cause this issue. The first thing I usually check in this case is the run/start capacitor(s) some machine use 2 or a dual element cap. If the cap is swollen 99% it is bad. Since it spins up it probably is not the contactor but checking the voltage drop across line to load for l1 and l2 should be low at the most a few volts when pulled in. Next an amp clamp it is possible your compressor insulation is failing check the amp draw on the contactor. If the amp draw is high the last check would be to use a megaohm meter on the compressor with power off l1 and l2 to ground is usually above 10meg at 500v some times as high as several hundred mega ohms at 500 up to 1000v. The reason for the mega ohm meter or never test is to see if the Freon has gone acidic and eaten the varnish off the wires. This happens when moisture gets in the system.

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