Posted by Jon Hagen on April 24, 2009 at 18:16:59 from (12.175.230.58):
In Reply to: Air conditioning help posted by Bill in IL on April 24, 2009 at 12:51:11:
Before you do anything, you need to get a gauge set on there to see what the low / high pressures are.
If this is on a R12 to R134a conversion, The 80 % rule that works fairly well on automotive systems, will almost certainly get you overcharged on an AG application.
I have found that charging a converted system is best done by vent temp alone. add enough R134a to get the system working, them add more, a few ounces at a time until adding a bit more (2 oz) does not produce a further drop in vent temp. This is the "sweet spot" that will give maximum cooling with minimum high side pressure. Adding more refrigerant beyond this point will actually reduce cooling and the high side pressure gets nuts real fast. I have done many of these conversions, and find this charging procedure produces the best results.
I hope your unit is just overcharged, as many compressors with reed valves like the old inline York pumps will see exhaust valve damage if slugged with liquid refrigerant during charging. If an exhaust valve is damaged, the cylinders will fill with liquid refrigerant that backfed from the condenser. Restarting a compressor with a damaged exhaust reed valve will take so much torque to push the liquid refrigerant out that if usually smokes the clutch or drive belt. Its tough to throttle liquid refrigerant into the low side of those systems, so I will only charge them using vapor. If your filling it with the 12 oz cans, it helps to set the can in a container of warm water to "boil off" the liquid to vapor. I use only Ester compressor oil in a converted system, as it will tolerate a bit of mineral oil still in the system, where PAG will not.
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