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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,128
"one shop said to turn the tank upside down when filling"

That's how I do it too in the beginning while the motor is off.
After evacuating it for 3 hours I do the initial charge into the high side only with the tank upside down so liqued R134 is going in until no more is going in from the 30 pound bottle of R134 and the high and low side manifold gauge needles have stabilized.

Then close the high side valve, start the motor, turn on the AC, and charge with the tank right side up so R134 gas is going into the low side of the compressor. It won't hydrolock the compressor doing it this way and shops that know this do it to save time.

Getting the charge pressure just right with R134 is tricky because the high side pressure is so sensitive to temperature which raises a lot while doing the final charging with gas into the low side with the motor running. Getting it perfect is almost impossible so I just try to get it close.

Charging until the high and low pressures were just right with R12 in the old days was incredibly easy compared to R134. The little bubbles going by in the sight glass on the receiver dryer would disappear when the the high side pressure was correct with R12. You would get the coldest AC with R12 when the high side pressure was just a little on the low side.
Old 05-27-2017, 10:50 PM
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