I am recharging a completely evacuated a/c system on a 87 911. 24oz were added to the high port with the engine off. 12 oz were slowly added to the low port with the engine running and the compressor clutch engaged. Adding the next 12 oz through the low port results in freezing the coil. Temperature at the base of the expansion port reads 40 degrees. High side pressure is in the normal range (~150 psi). Low side pressure is above normal (~90 psi), indicating frozen coil is not passing freon.
Is there a different procedure for dealing with this situation other than waiting until the coil thaws out before attempting to add more freon? As a 609 certified HVAC tech, I am aware of low freon resulting in low pressure causing low temperature (boyles law). But I have never encountered a case where the coil freezes very quickly.
Thanks for any help.
dgc2
