Automotive Air Conditioning Information Forum (Archives)

nlt99 on Mon September 06, 2010 3:44 PM

Year: 2003
Make: buick
Model: rendezvous
Engine Size: 3.4L
Refrigerant Type: R-134A
Ambient Temp: 100
Country of Origin: United States

When I start the AC after the car has been sitting for several days I hear a fairly loud "thump", or "rap" or several of them in very rapid succession. After that first start-up of the AC it makes no noise running or re-starting for as long as I'm using the car. The noise sounds like it's coming from the expansion valve area (it's mounted to the fire wall on the driver's side) and I'm wondering if it is possibly stuck from sitting for a long time, then pops loose. Has anyone ever heard of one acting in this way?

Another reason I am suspicious of the expansion valve is that I have had very high readings on the high-side and low readings on the low-side while the car is sitting still.

Appreciate any thoughts! Nick

GM Tech on Mon September 06, 2010 3:57 PM

Sounds more like liquid slugging......a design issue....

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

nlt99 on Tue September 07, 2010 1:08 PM

Thanks for the reply!
This is a new issue, not something that has been going on for a long time. Does that affect your opinion? Could it be a case of over-charge?

Also, forgot to mention that the overly-high pressure on the high side, with lower pressure on the low side is at higher RPMs with the car standing still.

Thanks again! Nick