A/C Schrader Valves not holding pressure.
07-10-2006, 07:19 PM
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A/C Schrader Valves not holding pressure.
I have been converting my 72 A/C to R134a. Yesterday everything was back together. System evacuated, loaded with 36 oz., 95 degrees in the garage, low side 35, high side 300, inside vent at 62, not great but better than nothing. When I removed the gage quick disconnct from the low side fitting aft of the compressor, the refrigerant blew so I quit for the day. Today I replaced the low side adapter on the compressor block with a new one from NAPA. Pulled a vacuum, removed the blue plastic cover from the low side on the POA and lost the vacuum. Strange but maybe under a vac. the Schrader valve will not close. Pulled a vac. again and put one 12 oz can in, removed the plastic cap from the POA low side and that one also blew the refrigerant. When the three 134a adapters were installed, the Schrader core was removed from the R12 fittings and the R134a were screwed on. Two different valves that did not seal, what am I missing?
07-10-2006, 10:06 PM
#3
Your are correct, Schrader valves were never designed to hold vacuum, only positive pressure. You should always have a hose connected, or a cap in place. Richy and Robinaire make a core access tool that allows one to change a core under system pressure or vacuum....or just pull it out of the way for fast evacuation.
07-10-2006, 11:08 PM
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St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19
Do not remove the shrader valves, they are to remaine in the fitting. The 134a adapter screws over the outside of the r12 fitting but uses the same shrader valve.
Neal
Neal
07-10-2006, 11:10 PM
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Thank you, sjmaster. I now understand the primary seal on the Schrader valve for long term is the plastic/metal screw cap, not the inner core stem. When the cap or quick disconnect is removed, the valves have dumped immediately before they can be capped off. It was not a minor leak but a major pressure dump. That can not be typical as the A/C could not be put under pressure.
07-10-2006, 11:16 PM
#6
No, not typical at all. Minor leaking is typical after some years in service, especially on the high side. The tool is nice...it makes replacing a leaking valve a piece of cake......and removing the core really does speed up evacuation time. Are you using a vacuum gauge to ensure complete moisture removal??
