# Air conditioning gremlin



## Hjudge49 (Feb 25, 2015)

I have a gremlin in my a/c system that I can't solve. The system is working, blowing cold air, and everything is fine at idle. When I get on the road, the compressor starts cycling on and off. I can hear a hissing behind the dash as it tells the compressor to go on and off. Any ideas what is wrong? The entire system u dear the hood has been replaced. When I bought the car, the engine and tranny were out, awaiting a rebuild. When I picked it up, there were no a/c parts there, so I had to get brackets, compressor, muffler, etc. then we put in a new fan, condenser and evaporator.


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## geeteeohguy (Feb 2, 2008)

The AC is supposed to cycle on and off going down the road. If the compressor runs all the time, the evaporator will freeze solid and you'll lose all cooling. The hissing sound is most likely a leaking vacuum pot in the HVAC system under your dash that operates one of the blend doors.


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## Hjudge49 (Feb 25, 2015)

I can understand that it would cycle some, but it's cycling every few seconds. And it makes the noise behind the dash every time it cycles. Almost more like a connection, like a "pop" than a leak. Obviously when it cycles on and off, I can hear and feel the engine changing pitch. I would estimate it cycling about every 15-30 seconds.


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## geeteeohguy (Feb 2, 2008)

That's too often. Most likely a hair low on refrigerant. If you system still has a sight glass in line, you will see what looks like white foam if it is low.


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