Automotive Air Conditioning Information Forum

Iam converting a 85 vette to 134a and the 134a
Pressure Switch for the clutch has threads that are
Too large, .390 od. My high side fitting is .375. What
Do i need to do?

The so-called liquid line should have a threaded connection matching that of the high-pressure switch. Sounds to me like you might have an incorrect switch.

Probably has the 3/16th (smaller) service port.

I measured the hp service port threads, .375"

I'm not an expert on this, but the outermost dimension of the threads measures 0.375 or 3/8". I'm guessing that the actual dimension at the root of the threads is a bit smaller. So you would need a switch with that dimension.

I would order an R-134a conversion switch for an '85 Corvette with its location on the liquid line, not on the compressor, which might be a different size threading, although I'm unsure about that.

Does the car still have an R4 compressor?

They only made two sizes of high-side ports on older GM vehicles, 3/8" or 7/16".