HVAC making sound even when off

air-conditioningcompressorcoolinghvac

At Thermostat

  1. Fan was on Auto
  2. Cooling was On

Outside Unit was making noise.
Outside Unit Fan not coming on at all

Next to the compressor on the Wall there was On Off Switch, I turned off power from the outside unit but it still kept making that noise

https://www.youtube.com/watch?v=CYYfuzDp5DU&feature=share

I went inside turned off the Cooling and noise went away

It has two capacitors
30uf and another small one 5uF

Unit is Lennox

3035hvac

  1. Is the issue with my capacitors?
  2. Can i replace these two capacitors with a single 35uf one ?
  3. Or i am thinking it completely wrong and it's something else?

Best Answer

Sounds like contactor chatter. Could be a bad contactor, or not enough power on the coil.

Basically, the contactor is closing and opening really quickly. This happens when the coil doesn't create a strong enough magnetic field to hold the contactor closed.

Depending on the cost of a new contactor, I'd probably just pop in a new one. If it doesn't fix the problem, you'll have to troubleshoot further. If you have (or can find) the manufacturer's specifications for the contactor, you could measure the contactor coil resistance and compare it to the spec.

You can also check the voltage of the control wiring going to the contactor coil.

  1. Remove the low voltage wires from the contactor, and position them so they do not come into contact with each other or anything else.
  2. Set the thermostat so that it's calling for cooling.
  3. Use a voltmeter to check the voltage between the two low voltage wires.

You should measure about 24 volts (assuming it's a 24 volt control system).

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