AC Recharge Help - won’t take 3rd can.

[Yukkman]

Had to replace low side schrader valve. So I evacuated it, bought gauges and pump. Leak tested. Pulled vac and let set for an hour, no drop.

Went to charge today and compressor wouldn’t come on. I jumped it via the sensor on the accumulator. 1st took awhile. 2nd can was slow too. I read about heating up the can and that helped. Got 2 cans and it won’t take a 3rd and it needs 4.

I heard a hiss which sounded like a blow off exhaust somewhere. I used a refrigerant leak tester and it started beeping at the accumulator, right were the tip is in the photo. Don’t see and oil though. How’s that possible if on my leak test it held -30 for an hour? Would this cause the AC from not taking in 2nd and 3rd can?

 

[Donal]

System plugged up. When a system is opened, for repairs, replacing components, repairing leaks, etc. Recharging with nitrogen or such and checking for leaks is standard procecure. Replacing the drier is required on automotive systems. If no leaks are present or detected, then the system can be evacuted with a vacuum pump or a venturi evacutor. When vacuum reading is around 15-16 inches of mercury, and holds that reading for an hour or so, then the refrigerent can be added.
Note that 30 inches of mercury is theretical and not achievable, even a sealed system like a freezer. The mechanical seal the the automotive compressor does not like low vacuum conditions. Jumping the pressure switches is not recommended because the system does not have the protection needed.

 

[rockola1971]

That blow off sound is exactly what it sounded like....a blow off from the overpressure valve. You might have a leak at the drier welds or the low pressure switch housing as noted by your leak detector and it may be very slight as to not show up on a 1hr vac test. You likely have a plugged up orifice tube and any time you open up the system you should atleast change the orifice tube if not the drier as well.