Another strange AC problem

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?

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.)

Thanks. Going to replace the ac compressor relay after I fine it.
Not sure of the location. any ideas? can't find it in my manual or
online.

On Sun, 24 Jul 2011 18:38:11 -0400, Mac <(E-Mail Removed)> wrote:

>Thanks. Going to replace the ac compressor relay after I fine it.
>Not sure of the location. any ideas? can't find it in my manual or
>online.


Nevermind, I figured it out.

Mac <(E-Mail Removed)> wrote:

> Thanks. Going to replace the ac compressor relay after I fine it.
> Not sure of the location. any ideas? can't find it in my manual or
> online.

Got these? http://neomiata.com/garage/index.php...ring+Diagrams/




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On 7/24/2011 8:51 PM, XS11E wrote:
> Mac<(E-Mail Removed)> wrote:
>
>> Thanks. Going to replace the ac compressor relay after I fine it.
>> Not sure of the location. any ideas? can't find it in my manual or
>> online.
>
> Got these? http://neomiata.com/garage/index.php...ring+Diagrams/
>
>
>
>
I hope the relay fixes the problem. Personally, I'd likely see if the
A/C radiator fan is running after the compressor kicks out before I
replaced the relay.
On the other hand, the relay switches an inductive load, and after
twenty years, it very well might have worn out.

We had an 89 Mazda MPV that seemed to "eat" relays.
A/C relay, Rear defroster relay, relays inside the turn signal module,
electric "kickdown" relay, Overdrive relay, and so forth.
The typical failure mode was contacts heating up, melting plastic, and
then the contacts would not close. No shorts were ever found.
I believe the relay mfr over spec'd the relays in the MPV since the
failing relays were all the same part number, except for those in the
turn signal module, which were made by the same mfr.