AIRFLOW unit R-22 8 tons, did a compressor change about 2 years ago. New Liq line solenoid valve and filter installed and a new moisture/liquid line sight glass installed. Ran great all this time. Started getting low pressure trips. After checking super heat: 50 degrees!, the charge (clear sight glass). Low side pressure was around 35 PSIg, high side around 200 and sub cooling was high. The distributor lines from the TXV were iced, the valve body cold. Removed the sensing bulb and warmed it up and saw no changes in pressure so we figured we might have a bad power head or clogged filter screens. Was about to pump it down and do a tear down on the txv and decided to check for charge migration just for kicks. After warming the head with a torch for a few minutes without much change, the unit started to improve. We re-attached and insulated the bulb and it has run fine for about two weeks and now the symptoms are back. Is this sounding like Power head? Would have thought that moisure/wax would have been taken out by the filter drier, so whats left?