I am a builder. I have a homeowner who has 3 Trane A/C units. It took a while to distinguish which unit was squeeling. but we now know that when the second floor unit comes on the A/C compressor on the outside make a loud squeeling noice that wakes the homeowner at night. It makes the noise for 30 seconds or less. My sub that installed the units is having a hard time figuring out the problem - mainly because the noise does not last very long. Any ideas?
Thanks
:confused:

Are you sure it is the compressor and not the fan motor/blade assembly?

Usually when a compressor makes that kind of noise it indicates.
Compressor starving for oil on start up
Wrong flow rater/piston for evaporator or TXV wrong size/out of adjustment.
Incorrect refrigerant charge.
Bent of kinked refrigerant lines.
Contact the manufacturer. They may have run into this before.

Could be what you say - may not be compressor. All I can say is it comes from the outside A/C unit for 2nd floor. The A/C works great - good cooling - no other noises. If that outside unit was on the other side of the house it would not be an issue.:D

2nd floor??? Did you use oil traps if necesary? Usually the oil will come back to the compressor from a elevated evaporator but no always.

Thanks for the advice - I will check w/my HVAC contractors. They will be out there on Thursday to try and investigate it again.:cool: