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Low Side Reads High PSI

Mustang on Fri April 04, 2008 11:49 AM User is offline

Year: 1990
Make: Ford
Model: Mustang
Engine Size: 302
Refrigerant Type: r134
Ambient Temp: 80
Pressure Low: 150+
Pressure High: 135
Country of Origin: United States

Replaced my A/c on the mustang last fall. Used an old compressor and new drier/line. I flushed everything, vacuumed and refilled with r134.

Everything worked good last fall with vent temps of 40 degrees. This spring I tried to use it on a couple of warm days and noticed that it's not cooling anymore. I suspected a leak and low charge but when I hooked up the gauges to add freon I see that the low side is reading very high. Off the carts on my gauges... probably around 150 - 200psi.

I read somewhere that this can be an indication of compressor failure. Maybe a bad internal valve. IS that right? I noticed a buildup of a black substance around the compressor? Black death maybe? The compressor is cycling and doesn't make any abnormal noise. Just not cooling.

mk378 on Fri April 04, 2008 3:05 PM User is offline

Really seems like you're measuring wrong. Are you sure you have the adapters on the right ports, and the hose couplers are engaged to the car fully? There's almost no way for the low side to be higher than the high side. Also the compressor should not cycle with those pressures.

Chick on Fri April 04, 2008 3:20 PM User is offlineView users profile

Are you sure the compressor is coming on? are the wheels on the gauge set closed when taking pressures, and as stated above, no way can it cycle with those pressures, you may here a fan coming on and off?? If the compressor is not coming on (center hub turning) then jump the cycling switch and see if it comes on and blows cold.. That or the wheels on the gauges are not shut...Let us know..

Email: Chick


Freedoms just another word for nothing left to lose

Mustang on Sun April 06, 2008 10:57 AM User is offline

OK yeah I was doing something wrong.... This is only the second time I've used these gauges.

I went and checked again and I was getting around 20psi on the low side and I think 85psi on the high. Added some freon and temps came way down. Don't remember what my final pressures were because I did find that I have a leak so now I've got to deal with that... Luckily it's in a spot that should be easy to fix. It's leaking from the high side service port. I think it's a bad needle. Wish there was some way I could fix it without evacuating the freon. Hopefully that won't cost too much.

Thanks for the help.

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