Mechanics

MODELS POOR COOLING

1999 Volkswagen Other

Air Conditioning problem
1999 Other Volkswagen Models 4 cyl Front Wheel Drive Manual 110, 00 miles

I have a 1999 VW Cabrio. Car is cooling, but not as well a before. Inspection of the A/C system doesn't reveal any obvious leaks. Air out the vents is only 65 deg. High side pressure is 235 psi and low side is 67 psi @ 1500 rpm. When the radiator electric fan kicks on the High side drops to 190 psi and Low side stays at 67psi. Conditions : OAT 81 deg. Dry bulb, 74 deg. Wet bulb, and 74% RH. The low side seems high, but I can't confirm that as I don't have any manufacture numbers.
I was thinking the low side should be around 25-35 psi. The high side appears to be close to normal (which I think is about 200-225psi). This system has never been touched since the day it was new, so it hasn't been overcharged by some tech. Any thoughts on this system would be appreciated.
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Rundawg
August 4, 2008.




You are correct, the low side is too high. Is this an expansion valve system? If so the problem may be that it is plugged or not working properly

Tiny
Jack42
Aug 6, 2008.
No I don't think it is an expansion valve. I was hoping someone would have a VW manual for that model year, that would confirm it. It appears to be a fixed metering device, which would lead me to believe there is a restriction possibly in the suction line after the service port, down stream of the evaporator and before the compressor. Is there normally any other filters on the one-piece molded suction line that could cause a restriction? Then again, if that was the case, wouldn't the liquid line(head pressure) pressure be low? What suction pressure is normal when the system is operating properly? Thanks.
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Tiny
Rundawg
Aug 6, 2008.
A restriction does sound right on the suction side. It should be around 35 when fan is on and ilding. You can find an online manual here. Usually the only "filter" would be the orifice tube, but like you stated it would cause high side pressure to increase as well

http://www.2carpros.com/kpages/auto_repair_manuals.htm

Same software we use in shops, closest thing to a VW manual.

Tiny
Jack42
Aug 7, 2008.

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