Never seen one go bad---but if there is dye there- it did not get there any other way- but a leak---change it out..

It is my experience that all relief valves are universal- will fit most any compressor- threads are the same, o-rings match...try a used one off a scrap compressor- or a core compressor at the dealer...should work

If you put sealer in it--no respectful mechanic will work on it-- they do not wish to plug up their expensive recovery equipment....

A leak that big can be easily found with a good sniffer, dye and black light with UV glasses...

One can only hope you have shut off the valves on the gauge set after charging-- otherwise you have created a bypass through the gauge set.....

I've seen two orifice tubes in similar units, and also have seen no orifice tube in front- it was missing- put one in, in the proper location and all was fine. Look for the OT dimples at a connection behind the tee-- also look for an OT in condenser outlet connection- there should NOT be one there.....

Why do you suspect expansion valve- ? when the number one cause of automotive a/c failure is loss of refrigerant due to a leak? Check your refrigerant charge by having it extracted and weighed and compared to factory labeled amount for your system. That is always the first diagnostic step. You canno...

Don't use a test light - use a DVM - digital volt meter- and check the three wires as referenced below- do you get signal confirmation? black wire is ground gray wire is 5volt reference or feed red wire is the return voltage which is proportional to refrigerant pressure- should vary with pressure - ...

Quit calling it a switch--if there are three wires it is a pressure transducer- sends variable pressure data to ECM to decide whether to turn off compressor for too high or too low pressure- can also command any auxiliary fans...Never try to "jumper" a three wire "switch"

No compressor lock-outs on GM trucks- you most likely have a high side pressure transducer (3 wire) issue- located on high side line from compressor. Never jump this connector- it has a power supply input (5v), a ground, and a signal return that is proportional to system pressure- 0 to 5v return sig...

The valves are not designed to leak, the caps are designed to be the primary seal. If you are running without caps, then that is your choice. Don't believe it? Do what I do, use your sniffer with cap off-- it goes nuts, put cap on (with good rubber seal inside) snug it down - wait 5 minutes- re-snif...