My initial post was deleted as "DIY" for including too much information about system pressures. Evidently consumers of technical services are expected to remain uneducated about their systems.

In any case, the service guy arrived and diagnosed the system as being low on refrigerant. He did a sniffer test at the condenser and evaporator and found a possible very slow leak at the evaporator. I was surprised that he had neither recovery machine, nitrogen gear, nor a micron gauge. He examined the piston and pronounced it clean. He recharged and said to call him again if the evaporator frosts up. He also said that the filter-drier called out in the parts list was actually just a strainer that would not clog. The serviceman was recommended by the local Johnstone Supply.