Posted by Jon Hagen on May 06, 2009 at 12:25:11 from (12.175.230.36):
In Reply to: A/C help again posted by Bill in IL on May 06, 2009 at 06:24:10:
"Currently have about 36 ounces in the system and its still low. The sight glass still shows air bubbles and the low side pressure is only 15 the most I have seen so it cools good but will freeze the evap coil like that."
You may be overcharged with those pressures on a 70 degree day using R134a. 15 psi low side is not out of line with 70 degree air temp, 190 on a 70 degree day is border line high (rule of thumb is 2---2-1/2 times air temp is normal high side pressure.
NEVER EVER use the sight glass to determine charge level when charging a converted system with R134a. Little globules of Ester oil floating in the refrigerant looks exactly like bubbles. If you have a clear site glass running R134a, you are very overcharged, which would explain the higher high side pressure.
What works best for me is to add just enough R134a to get the system cooling and add more, 2 oz at a time until a vent thermometer shows no drop in vent temp with the addition of a couple more oz of refrigerant. STOP at that point, that is the sweet spot that will produce maximum cooling in a converted system with minimum high side pressure. Adding more can actually decrease cooling and high side pressure goes crazy high.
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