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93 Chevy Corvette, automatic temperature control. it blew the condenser out, so we decided to switch it to r134a. flushed the system, replaced all o-rings, condenser, drier, orifice tube, and filled with correct amount of oil.

in the process of adding the r134a, the compressor cycled on a few times, then quit. it will not cycle back on. we jumped power to the compressor and it spins, so we checked the high and low pressure switches. the low pressure switch came out ok, but when we went through the factory diagnostic tree for the high pressure switch (which is actually a pressure transducer) we discovered that it tested bad. we replaced it, only to have the same problem. the new switch tested bad just as the original one did. the computer is throwing a code 66, which says the pressure is low. any ideas?


Did you replace that pressure switch with the same original equipment part designed for R12, or one designed for R134a?  Most AC parts suppliers offer a lower pressure retrofit switch, and recommend using one due to the pressure differential between R12 and R134a systems.


You mentioned the problem occurred "in the process" of adding refrigerant. Did you eventually get the proper amount of R134a in, (you only need to add about 85% of the original capacity of an R12 system when retrofitting it to R134a), or is it still undercharged?

Tom Dayton
JS Auto Supply

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