On 7/21/2011 6:03 PM, Mac wrote:
> Have a strange AC issue. 1990 Miata. New compressor, expansion valve,
> pressure switch, drier. All gauge values look good. Run it for a
> while, no set time. Then it will just stop and the rpm's will jump up
> to around 2000. can hit the switch and turn of the ac and the rpm's go
> back to normal. figure it is electrical at this point. any thoughts?
>

The RPM jumps because the compressor clutch is dis-engaging.
I'm not that familiar with a 90, so I don't know if the system uses an
"amplifier" or not. If possible, I'd try to see if the compressor kicks
back in when you cycle the A/C switch. There is a possibility that the
pressure switch is shutting down the system, or as you said, some sort
of other electrical fault. (Fan, relay, etc.)