A/C compressor hum

[Clifftall]

I cleaned the fins on both coils They were quite dirty and I was experiencing a musty odor at start up. As soon as I restarted the unit a low hum appeared when the compressor kicked in. The unit itself is much quieter and cools great but there is that hum. Any ideas??

[TXiceman]

You will normally have some noise, hum or such from a running compressor. All of the newer units are compliant scroll compressors and the compressor and motor will make a little noise since they do rotate at 1800 RPM.

Ken

[Clifftall]

Thanks Ken , its just that it never did that before and the other one that I also cleaned doesn't make that noise.

[TXiceman]

Since it is a new noise, you need to check that you got everything back together correctly and tightly. Make sure wires and lines do not rub and are secure. If you had some sheet metal loose, that could be the source of the noise. while it is operating, careful of the fans and any exposed electrical, use a stick to push on various parts to see if you can locate a problem child.

ken

[RV Wizard]

Not sure if you removed the unit or not but check the torque on the bolts that hold the unit to the roof. The ones that are accessible from inside with the ceiling trim removed. If too loose the unit can leak If one is too tight it can twist the base pan of the unit and cause noise. If the roof gasket is flattened out all the way, it should be replaced and when installing only compress it down to one half its thickness with even torque on each bolt. Another possibility could be the compressor is off one of its suspension springs, a weak spring or the whole compressor is shifted and foot is contacting the base pan.
Good luck and let us know what you find.

[Clifftall]

Quote:

Originally Posted by RV Wizard Not sure if you removed the unit or not but check the torque on the bolts that hold the unit to the roof. The ones that are accessible from inside with the ceiling trim removed. If too loose the unit can leak If one is too tight it can twist the base pan of the unit and cause noise. If the roof gasket is flattened out all the way, it should be replaced and when installing only compress it down to one half its thickness with even torque on each bolt. Another possibility could be the compressor is off one of its suspension springs, a weak spring or the whole compressor is shifted and foot is contacting the base pan. Good luck and let us know what you find.

Thanks Mike. I did not remove unit and new gaskets were installed last year. I'm confused as to where the compressor is. I see a fin/coil in front and another in the rear. Don't know which is condensor and which is evaporator. I cleaned both. I saw the fan and fan motor. How do I recognize the compressor? I will take the sheet metal off again and retrace my steps to see if anthing looks loose. But the noise starts when the compressor kicks in.

Cliff

[TXiceman]

The condenser the part that blows warm air on the roof. The evaporator is the coil that blows cold air inside. The compressor is the round black thing up on the roof behind the condenser coil...presuming this is a roof top unit.

Make sure that none of the lines on the outside section are vibrating. Make sure the bracket holding the fan motor is secure and the fans are not hitting the fan shrouds.

The units built over the past ten years or so, have a thinner pan under the unit and can be easily warped if not tightened evenly or is over tightened.

Ken

[Clifftall]

Thanks Ken ans Mike. Problem solved. There was a very thin ( 1/8" ) copper tube that I must have bent out towards the shroud and was vibrating. I gently bent it back. Life is good at IRV 2.

[RV Wizard]

Good to hear, thanks for the update.