Automotive Air Conditioning Information Forum (Archives)

ghoward705 on Fri August 13, 2010 10:06 PM

Year: 2005
Make: Buick
Model: Terraza
Refrigerant Type: r134a
Ambient Temp: 104
Pressure Low: 90
Pressure High: 250
Country of Origin: United States

This car's A/C has been marginal since we bought it in early 2007. Today, we picked it up from dealer after getting a quote of $3200 to replace the entire system, all lines, evaporator, condenser and compressor. A/C tech says system is contaminated with metal particles from the compressor. initially, two years ago, I could add R134a until the high side was reading 250 psi. At that point the high side gauge needle would start shaking. If I added more r134a, the pressure went up but the high side gauge needle shaking increased. When the needle was shaking the temperature of the discharge air would increase. I did not record the low side temperature at that time but it seemed reasonable. The cooling has always been just marginal and was uncomfortably hot during summer time trips. Today, the system was completely empty when I retrieved the car. I added 3 oz of oil and charged the system. The high side gauge needle did not vibrate at 250 so I stopped there. When, my wife returned from a shopping trip, she said that the A/C was not working. I checked it and it was blowing just hot air. An hour later, I took the car out and the A/C was working, not good but cooling enough that it was more comfortable than with the windows open and the 104 degree afternoon temp. I believed that the shop must have allowed air into the system, so I discharged the system into a spare tank and refilled the system with fresh r134a. There is no visible dryer or collector on this system. At present the high side pressure at 1000 rpm is 275. The low side pressure is 85. I had the wife change the rpm to 2000 and then to 3000. At 3000 the high side pressure went to about 350 and then the compressor shut off. So I bled off some of the r134a and retested at 3000 rpm. The compressor stayed on. remarkably, the high side gauge needle was almost steady at every pressure until the compressor shut off. I did not see the low pressure gauge during these 3000 rpm checks. First, I think that the A/C system on this model is too small for Texas summers. The next concern is that the low side pressure seems too high. What could be causing the low pressure to be too high and yet the compressor can drive the high side to the pressure limit. I have an infra red temp gun but I can't get repeatable readings. The under the hood temperatures are just too high. While I was adding gas I have checked the temperature in the past and could see the low side line temp decreasing. Today, it was too hot to get reliable readings. Any help would be greatly appreciated.

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George