Auto Air Conditioning & Heater Repair: ac on 97 chr t&c 3.8L, hi psi, dual system

Question
the compressor runs shortly and suntion psi is 140 then is shuts down. the hi psi is 40 and the psi won't equalize after shutdown for sometime. the system worked fine last night then this morning this happened. this is a dual system also.

Answer
Hi Terry

Your suction psi comes from your blue gauge and your hi form the red one.  I think you meant 40 suction and 140 hi.  If so the hi side is too low  add some more freon and make the hi side go above 180.  If it does up but then comes down below 150psi your expansion valve is definitely bad.  Its hard to tell on a dual system which is really bad but usually the front one is the one that causes the most headache.