wont hold vacuum

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wont hold vacuum

Postby kabuelich » Fri Feb 21, 2020 5:18 pm

Hi, I am working on a 1988 Corvette system.It had very little gas in it, I powered the clutch to see if it would engage and it did. I replaced the accumulator and orifice. I replaced all the o-rings. It will evacuate down to 29# but when I turn off the pump it immediately drops to -10# then slowly goes to 0. I bypased the condenser, compressor, rechecked all the o-rings and schrader valves, sensors, cracked open the lines and blocked off each one individually to try to narrow down the leak but every time it still pulls to 29 but wont hold when I shut the pump off. I pressurized it to 90psi with air and it holds there so I dont understand why it will hold under pressure but not vacuum. I couldnt feel or see any leaks under pressure. I evacuated it again and it still wont hold. Is the compressor bad ? I dont know what else to try.
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Re: wont hold vacuum

Postby Dougflas » Sat Feb 22, 2020 4:57 am

you need to put some refrigerant ( 1or 2 oz) and nitrogen. Use an electronic sniffer to find your leak. Do not forget to check your gauge set.
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Re: wont hold vacuum

Postby Tim » Sat Feb 22, 2020 8:07 am

It is odd but happens when a seal will hold under vacuum and leak under pressure or the other way around. Just the type of pressure placed on the seals. As stated the first step is a solid leak test.
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Re: wont hold vacuum

Postby ice-n-tropics » Sat Feb 22, 2020 11:23 am

Vacuum = a lot to do about nothing.
Modern compressor dual shaft seals have a outer elastomer above atmosphere pressure lip seal and a inner teflon compounded under atmospheric pressure
seal. The inner seal is often scratched during sloppy or dirty service replacement (w/o a proper shaft seal protector).
Positive pressure leak detection methods are ineffective for shaft inner seal leaks.

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