What is causing this problem?
 

A little background: my a/c was blowing warm air. Sight glass showed no freon. I took the car to the shop and had the system filled with r-12. Presto... Cold air.

A week or so later, I am driving with the A/C on. The air was cold one moment then warm the next. Later, I look in the engine bay, and the compressor belt has somehow slipped off of the pulley to the outside of the compressor. The belt is a little nicked now.

I'm at a DE when I notice this, so on my way out, I have a more talented mechanic put the belt on. System works again. Ice cold air.

A couple of hours later, a high, high pitched squeal came on. Only comes on when the A/C is on. It only does it at low RPMs, and I THINK only when the engine is cold.

I took a look in the engine bay with the engine running and the A/C off. Everything looks perfect. With the engine off, the compressor belt feels tight. When I turn the A/C on, the compressor belt vibrates a lot. More than vibrates... It looks like it is going to shake the entire engine out of the compartment. Then the noise happens. When it does, the entire compressor pulley stops spinning. Not just the clutch, the entire pulley. I would have thought the noise was the belt slipping, but no, the belt freezes too. The whole belt and pulley just stop, and the screeching squeal begins. Lasts a pretty short time -- 3 seconds or so, and happens at random intervals.

What gives?

Sounds like your need a new/rebuilt compressor. The squeal is probably the (stopped) belt rubbing on the crank pulley (and probably the reason for the thrown-off belt in the first place). AFAIK, the belt would only "stop" if the clutch is trying to engage a compressor unit that is seized/seizing. You will probably burn the clutch up too if it's not toast already.

Your theory matches my fear. I guess I'm curious, though -- why did the problem only begin once freon was added?

Maybe the compressor needed to have it's oil recharged, and it wasn't done at the time of your refridgerant charge. Or maybe it was recharged, but with an incompatible oil? Just guessing.

I hope I don't have to replace the compressor, but if I do, here are some questions:

1. Do I have evacuate the R12 I just had added? (Have a shop do it, I mean.)

2. Can I rebuild or replace the compressor myself?

3. How do I further diagnose whether it is the compressor?

4. In what order should I attack the problem? Belt first, then have oil added, then, if that fails, rebuild the compressor?

5. If I have to rebuild the compressor, is it worth while to upgrade to a newer type compressor? (I drive an 82 SC.)

Did they put in too much freon? is the high pressure going too high?
My belt's return side flopped a little also even thoguh it appeared rather tight. I tightened it some more and it seems to have settled down.

Time for a new compressor, good time to upgrade to a sanden if you still have the york.

The problem was probably there before they added the freon, however when they refilled the system, now the compressor must actually compress the freon so there is an increase load on the compressor. The a/c shop that refilled the system should be able to evacuate the freon, and they should be able to let you know how much freon was evacuated. (This can be determine by placing the freon holding tank on a scale and noting the weight of the scale before and after the evacuation.)

RUF, does that mean I can reuse the freon instead of shelling out $$$ for new freon? That'd really add insult to injury.

Freon is being recycle right now because it is no longer being produce in this country and any other countries that signed the Montreal Protocol against destruction of the ozone layer.

The shop may give you a credit for the freon that they remove from your system, if not look for a shop that will give you credit for your freon. By law they must recover any freon in an automotive system. Also by law they are not allowed to "top off" any system, but must find any leaks.

There is a caveat to this, if your compressor suffer "Black Death", they may decide not to recycle the freon so they will not give you a credit.

Do a search for compressor black death.

Strother, you have the same year and same color PORSCHE as me, except mine is a TARGA.

Edit

If your compressor did suffered the "Black Death" you need to have the entire system flush. Just putting a new compressor back in will just mean that the new compressor will fail sooner.

sounds like the typical compressor seizure that would happen if you ran the a/c with the engine lid up too long. caused by the lack of airflow through the condenser. the front conderser has a fan. is it working?

Hmmm... JW, that's interesting. When we put the belt back on, we ran the A/C for 5-10 minutes with the lid up, watching to make sure there was no problem at first, then talking and forgeting about the lid next. Is that long enough to cause the problem?

I'll check the front condenser fan. The air is so cold that I would guess the fan is working. With a seizure caused by lack of flow, should I be looking at a rebuild or a replacement? And if I replace, is it worth it to move to a Nippondenso?

With the lid in the open position, there is not enough air flow through the condenser. As the condenser gets hot the pressure on the high side of the system is also increasing.

10 minutes is more than enough time depending on the outside temp for the pressure to increase on the high side to cause damage to the system.

If you don't want to replace the hose in your car, stick with a compressor that has flare fittings. The later nippondenso compressor has o-ring fitting. You can also buy adapters to convert the o-ring fittings on a compressor to flare fittings.

A brand new Sanden with adapter plate is probably cheaper than a Porsche Nippondenso and adapter plate.

Replacing the hose is probably the most expensive part of the a/c upgrade due to the labor involved in removing and replacing the existing hose.

Cool, RUF. The temps were pushing 95 that day. Probably warmer than that in the sun.

Any pictures of your Targa? The platinum metallic has really grown on me.

Picture of my Targa next to a Platinum Metallic Turbo at last year Tweeks Fest aka Mid America Funfest.

http://forums.pelicanparts.com/uploa...1119391273.jpg