1992 Mitsubishi 3000GT AC Compressor Won’t Come On

Reader Question Dear Sir,

I have a 1992 Mitsubishi 3000GT SL on which I have just changed a re manufactured A/C compressor/new clutch along with a new dryer and an expansion valve, charged the system with 8 oz of oil needed for R-134 and I also charged it to about 2/3 of it’s capacity.

However, as I proceeded to charge the system, the screen on the A/C control unit has always switched from the picture of snow flake to a red dot in about three to five seconds. Even as the A/C control unit works fine and everything else like blower and screen works, the entire sA/C system with fans and compressor turns off.

If I drive the car, the system works fine but as soon my RPM drops on the intersection or near when I am slowing down, this problem always occurs. If I just start the car and run it higher RPM, two things occur: In the beginning, the system worked but last few days it turns off; the red indicator dot on the control unit signals that the system turned itself off.

I have installed everything properly, my mechanic double checked on that. A/C compressor belt is tight.

Can there be a problem with the compressor part like low compression valve or does the ISC unit have anything to do with that; or anything else?

I did the self diagnosis check and it sends me a “normal” signal.

My mechanic is puzzled. In my local Mitsubishi service, they have no idea, either.

Do you have a “cure”?

Thank You. Sincerely, Andrej

Hello there Andrej

I sent your email to my top a/c mechanic and he is stumped as well…sorry, but I have not seen or heard of this before and don’t know what to tell you to try next without being able to run some tests on the vehicle.
Sorry again,
Austin Davis

Dear Austin,

Thank you for your reply. I was actually able to fix the problem. I based my analysis on the fact that before I changed the A/C compressor, the old compressor has never triggered this problem; and based on that assumption, there was only a few possibilities left (after I have checked almost the entire system for a defect before).

One of them was a chance that the rebuilder of the compressor could have left an old electrical component on the compressor. Sure enough, upon the dismount and inspection, the speed sensor on the rebuilt A/C compressor was defective/old – actually beat up.

Since I’ve changed the component (you have to also change the A/C thermostat as it is one assembly unit), and proceeded to recharge the system, the system held and it still does.

It actually works beautifully now.
I think I owe you the explanation since you have been kind to reply, even though you could not provide me with an advice. Maybe this will help you in the future with your next customers.

Thank You.
Sincerely, Andrej

Posted in: A/C and Heating

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