If the 50 is with the compressor ON, then you're overcharged. Your compressor has no chance in that situation to cycle off. The specs for your compressor is 25-33 psi, Low Side pressure (ie, compressor ON).

The compressor cycles off in normal operation to prevent freezing up: "compressor is connected in series with the low-pressure switch, high-p switch, and safety switch . . . Low-pressure switch (pressostat) turns a/c compressor on and off to maintain pressure within limits" (from Volvo N.A./Mitchell manual).

As I recall (though not 100%), the low-p switch cycles the compressor off around 20-22 psi??? If you're overcharged (very common among DIY'ers I think), that might be your problem. Is your a/c cold as Hades, like 38F inside ducts? (Temp's not a reliable measure of overcharge but just wondering.)