Rear ac unit on Yukon screaming

[Elmerwood]

Hello everyone,

My wife's 2003 Yukon has a screaming rear ac unit. I've unplugged every motor and blend door actuator on the unit and it's still screaming. I work a hydraulics and the noise reminds me of oil going over a flow control or by a pressure relief. While it's screaming the lower portion definitely feels like where the noise is coming from when touching the unit. Had anyone run into this situation before? I'm going to try to link the short YouTube clip of it screaming.

 

[Bill 1960]

If you can make it stop by disengaging the ac mode then it could be the thermal expansion valve. I have not heard one chatter like that but that is a flow control valve where the refrigerant flashes from liquid to gas phase.

I would try various modes of operation fan on/off; AC on/off etc. to isolate what components are in use when the noise appears.

 

[Elmerwood]

If you can make it stop by disengaging the ac mode then it could be the thermal expansion valve. I have not heard one chatter like that but that is a flow control valve where the refrigerant flashes from liquid to gas phase.

I would try various modes of operation fan on/off; AC on/off etc. to isolate what components are in use when the noise appears.

I've tried turning every knob in every position but yet it still screams.

 

[Bill 1960]

So it makes this noise with the HVAC system turned off?

The only constant I can imagine in that case is it’s coolant running through the heater core. Which I can’t see having the pressure or velocity to generate that sound.

Does it ever change intensity or frequency with changes to any control?

 

[Elmerwood]

So it makes this noise with the HVAC system turned off?

The only constant I can imagine in that case is it’s coolant running through the heater core. Which I can’t see having the pressure or velocity to generate that sound.

Does it ever change intensity or frequency with changes to any control?

 

[Elmerwood]

With the rear ac off and the front running it makes that loud noise still while the car is idling in park. If I through some RPMs to it the noise goes away or lessens. When I turn the vehicle off you can hear the noise in the back wind down if you will for a few seconds after the vehicle is completely off.

 

[Bill 1960]

It’s the expansion valve. There’s only one compressor, so it’s pressurized any time the front is running.

 

[Elmerwood]

It’s the expansion valve. There’s only one compressor, so it’s pressurized any time the front is running.

Thanks for the info Bill. I ordered the expansion valve from Amazon $20 and when I had time ran it to my friends shop to use his AC machine to drain before performing the swap. Changed the part and recharged the system. I've put probably 100+ miles since and no screaming any longer (knock on wood). No I'm chasing a oil leak that I fear is coming from the rear seal :-(. Lucky that I have a lift at my shop at least.