DriveFast

1 year old '04 SL. At low RPM with A/C on I hear a high pitched squeak or squeal come and go. It's NOT the belts! It's in the cab. I kill the fan, still there. Kill the A/C it stops, restart the A/C it comes back.

Found a 1-2 owners with similar issues (no resolution) in a year-old Freshalloy thread. Will be taking it in soon and will likely need to explain my theory as these guys don't always look real hard (based on history).

This is the best explaination based on a Google search on A/C operation. Makes sense and yes it does sound exactly like the stretched ballon:

After many years of listening to air conditioning units, it is most usual that the squeal is from the metering device, (called a TEV or TXV for short,) allowing some of the refrigerant to pass through the closed seat from the high pressure side to the low pressure side. This squeal does not happen on the less-expensive units that have a fixed orifice that never closes off. An additional reason for the squeal is that the new Puron refrigerants run at over 400 psi pressures which forces refrigerant through the tiniest of openings at high speed, like stretching the neck of an inflated balloon to make sound.

The TXV seperates the high and low part of the refrigeration system. High pressure condensed liquid enters the TXV, as it leaves the valve a pressure drop is created due the amount of refrigerant metered in.

I'm looking for anybody with actual refrigeration experience that might be able to back this theory up. If I'm right it will be my luck this thing is in the firewall next to the evaporator......go ahead and trash my dash Mr. Nissan.

Redsand187

Well the TXV shouldn't be in the cabin so you shouldn't hear it through the vents.

If you want to confirm this, get a long screwdriver put it on the TXV, which is probably on the firewall near the heater core. Put your ear next to the end of the screwdriver, if you can clearly hear the noise, then that's what it is.

My guess would be it's more likely the blower motor then the Thermostatic Expansion Valve.

Robert_J

I think I may have this problem. For a while I thought it was alternator whine coming through the stereo until I found out it doesn't vary with the engine RPM. Then I heard it with the stereo turned off.

The sqeak/squeal is audible but not overly loud. I can drown it out by turning up the radio. Usually lasts between 4 and 10 seconds. Does this decribe what you are hearing?

-Robert

MaxMus

I'm curious if anyone else is having this problem as well? When I start the engine, I hear this really weird harmonic noise with the A/C on. When I turn the A/C off, it dissappears. I thought it may have been air in the coolant, but it's definately not that.


Sorry to rehash an old thread, but I am reading from the beginning of this forum up to today's date.

factorymax

I have noticed the same noise. Only notice when RPM is low. Sounds almost electronic as it is so hi pitched. Not a real intrusive noise, but I have often wondered what it is.

Mine seems to slightly change pitch with engine RPM, but only when I am going between 30 and 40 MPH and the tranny is in 4th or 5th gear. Lasts 10 seconds at most, but happens again after I speed up gently froma dead stop.

I have not asked the dealer about it, but I will at the next oil change.

MaxMus

mine is only noticeable at idle, in Park. When I put it in drive, I can't hear it. It sounds really weird, like some sort of electronic thing.