Compressor, Capacitor, or Condenser?

bjrscj

We just moved into a new home and everything was working great. Today, the HVAC unit supplying air to our lower level stopped working. I checked the furnace, and a solid red light was on, which is exactly what the working unit's light is doing. I checked the outdoor unit's 24/240v supply, and when I reset that, I began to hear a soft humming noise from the broken unit.

From what I've researched, the problem would seem to be electrical in nature, and would most likely lie with something like the compressor, capacitor, or condenser. The humming indicates I have power at the unit, but that it is not handling that correctly. I'd appreciate any insight as to the potential cause of this problem. Thanks.

Doc Holliday

Please be a little bit more specific. Is the inside blower motor coming on at all while stat set on fan, heat ? Is the outside unit not coming on while the inside blower is coming on while stat is on cool? What exactly is or is not happening and with which section of the system, inside blower motor or outside condenser? Where is this hum?

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Thanks.

bjrscj

The furnace works and blows air when set to heat. However, the furnace (indoor unit) is not blowing air when set to cool. When moved from "auto" to "on," the fan works.

The outdoor unit is making a soft hum noise from the rear. It sounds like it's coming from the area where the wires enter the unit. The fan blades do not spin at all.

Thanks for your help.

Doc Holliday

Is this the inside blower not running? Then yes, there is no diagnostic code for the board to flash when a capacitor or the blower itself fails.

You need a meter that reads microfarads (UF/MFD) to check the cap or any meter that reads a/c voltage and continuity (ohms) to check the motor but pretty much if a motor is receiving voltage and the cap is good but not running then the motor is shot.

If you do not have a meter than start by replacing the cap as it's the cheapest route, 10-ISH dollars. You will have to remove the existing cap and take it with you or write down the numbers from it and get the exact replacement. Graingers sells them.

If that does not work then again, if the motor is receiving voltage from the board and the cap but not moving then the motor is shot.

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Thanks.

Doc Holliday

Not a problem, we all live for this around here.

Just like in my previous post concerning the inside blower, the same applies to the outside. There is a run capacitor and 9 out of 10 times it will fail long before the motor will. Turn the breaker to the outside unit off, remove service door and look at the cap. Does it looked round on top or is there any oily jelly like residue all over it, both rounded on top and oily? Bad cap.

Also with power OFF at the BREAKER, try and spin the fan blades with the use of a long screwdriver or a straightened out metal clothes hanger, something so you can turn the blades. Does it spin freely?

Also, with the power ON to the entire system and the stat set on cool yet the fan not spinning, is the lid of the condenser where the motor is hanging from getting abnormally hot to the touch? These are all tell tale signs as to what to expect.


The humming noise you hear, if inside the service door of the condenser where the wires go into, is nothing more than the contactor being pulled in during a call for cool. It is there regarldess if it indeed is the contactor (some hum, some don't but all work the exact same), you just can't hear it with the unit on.

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Thanks.

bjrscj

The capacitor is definitely rounded on the top, so I'm assuming that's what the problem is. Thanks for your help!

Doc Holliday

Yup yup, that's it. Just make sure you get the EXACT same microfarad replacement.

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Thanks.