Connecting a charge hose isn't the answer...have the system discharged & PROPERLY recharged with the correct weight of refrigerant!

50PSI means little OR nothing! a normal system at rest at a temp of 70-80F will read at least 100psi. but again it isn't all about pressure but about correct refrig charge by weight!

YOU description sounds like a LOW charge of R134a not a bad valve!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator