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I put new dryer and compressor on 04 gmc truck I charged sys and shut motor off about 2 minutes I heard a hissing noise coming from fire wall do I have a leak in evaporator or does it have a pressure valve for when its over charged

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You were probably hearing the freon gas equalizing in the system.
When you add freon it is generally in liquid form. And it can settle in the bottom of the condenser and evaporator. Once the system is full and has been cycled a few times, it should not make much of a noise. You may want to check it in a day or two and make sure it is full. High side should read around 200-250 psi. at idle.

Posted on Jul 13, 2013


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air may have gotten into your brake lines. try bleeding your brakes. this will require two people

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SOURCE: A/C compressor cycles on/off

You could have a slow leak and the system is low on R134 and soon will stop running. The other thing to look for is the relay to the A/C compressor and switch it with an other relay or just replace it since there not that expensive. The pressure switch is an easy replacement to do, you just have to be quick so you don't lose all the R134 out of the system. Recap, recharge the system and get a proper reading on your high and low side A/C lines. To much R134 will also give you the same problem. Good luck and hope this helps.

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SOURCE: 1998 GMC Sierra- runs rough then stalls when

had this problem on my neighbors 98 chevy truck with the same engine !!
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SOURCE: Hissing noise when releasing brake pedal

Sounds like your brake booster but can't be sure until I know what kind of truck or car you have....

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SOURCE: A/C compressor does not engage for 10-15 minutes after start

you have a clutch gap problem, the a/c clutch has worn and the electric magnet can not pull it together. take your car to a local repair shop and ask them to set your clutch gap to 0.014" inch. this repair is simple and should cost less than 100 dollars

Posted on Aug 15, 2009

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