hold pressure but not vacuum

kskill on Tue August 07, 2012 9:50 PM

Year: 72
Make: chevy
Model: g20
Engine Size: 350
Refrigerant Type: 12
Ambient Temp: 65
Country of Origin: United States

72 chev rv shasta 17', g20 w/350 +york comp driving an ara add on. system was overcharged by local yahoo. told ran great for first 40 miles of chassis up rebuild shake down. i got it and the charge is flat. i mean flat zero. i normally do walk-ins, under counter and residential ref. nitrogen charge to find poss leak. not a thing. held 120 clean over night. discharge next after noon. vac pump with res grade yank down. acts like it has a hole the size of a pencil. re charge again with nitrogen held all night. vacuum again, same thing. any clues. thx k

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appliance service company thirty years old. i feel a hundred.

Leggie on Wed August 08, 2012 6:02 AM

paragraphs and sentences run on and capitalizations and etc do you have e p a 609? its illeagle to do cat ac even with 608
u dednti say how u hooked up them gauges so u know it mite be dat its the shudder varlves cuz them aint designed to hold vacuume

NickD on Wed August 08, 2012 7:57 AM

If you lost all of your charge, no doubt you have a leak. Better off to sacrifice a can of R-134a and use a sensitive electronic leak detector with a cool engine and a draft free space to check for leaks. You already know refrigerant is heavier than air, so have to check below all those fittings. Typically tell-tell signs of oil leakage.

Son with my help just completed a five year long war about his new York system, his HVAC guy said it didn't have any leaks. Went over there and found leaks in the condenser, poorly soldered fitting, and the evaporator. My son only managed to get his condenser changed and the fitting repaired last year, his HVAC guy insisted his evaporator was okay. This spring, lost half of his refrigerant, warranty was over, just told my son to talk to his HVAC guy to replace that evaporator under warranty or small claims court. He finally replaced it, let's see what happens.

He finally got an electronic leak detector, but doesn't know how to use it. His cure last year was to put in stop leak, only good that stuff did was to block 25% of his old evaporator and partially plug the expansion valve, that also had to be replaced. How does a guy like that stay in business? Tell you one way, by charging his neighbors 300 bucks to recharge the system each year, maybe his neighbors are dumb enough to pay that, but my son has a dad that knows better.

buickwagon on Wed August 08, 2012 8:09 AM

Unlike stationary units with electrically driven sealed compressors, engine driven compressors cannot be sealed. My suggestion would be to check out the compressor shaft seal. Rubber seals can often leak one way but not the other, and are more prone to leaking when the shaft is actually spinning compared to just sitting overnight. One trick I read about is to encase the end of the compressor with a plastic bag for a few hours or overnight and then stick the electronic leak detector in the bag to see if it captured anything.

Have you checked the oil concentration? Besides lubricating the moving parts, the oil helps somewhat in sealing as well.

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I've saved hundreds on service by spending thousands on tools.

AutoCool on Wed August 08, 2012 4:30 PM

An oring that wasn't lubricated before assembly or the connection was overtightened can deform and become "squished". If the oring is deformed on the inside of the connection, it might still seal under pressure (forced against the connection by the pressure) but not seal at all under vacuum. Lots of people overtighten oring connections thinking that will make it seal mobettah.

ice-n-tropics on Wed August 08, 2012 8:57 PM