Is that static pressure or the high side pressure? High side pressure should run from 180 PSI to 225 PSI when running at normal operating RPM. Low side from 20 to 30 PSI. Was R134A added when the system was empty and open to the air? If so you could have moisture in the system causing erratic operation. Could also be a sticky expansion valve ( if this model uses one).
One thing to try is to shut off the heater by turning a valve off on the block or pinching the heater hose flat. The heater will always win if it is stuck on.