I installedAC in my '96 Ranger 3 years ago - and it worked good for 3 years. It didn't work this spring so I topped it up with 134A and die, and it worked for about 2 weeks. I went at it with the UV light and found a big stain at the low pressure service valve. Had it into the shop today and replaced the shrader valve - no other leaks. How common is it for a shrader valve to fail "in service" (not while being charged or drawn down)?
With central AC systems, the parts houses sell replacement cores. So, there must be some demand for them. How common? I'm not sure. Wish I could be more help.
I think for the ninety six cents they cost it would be a good idea to replace them every time a system is "opened" (refrigerant removed and system drawn down or pressure tested) . There ARE tools made to replace the core without emptying the system -so I guess it's not an uncommon problem.
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