Macadoo

Last summer, after renovating the entire system, I got to run the AC for about half an hour before it fragged a belt. I replaced the belt, turned it back on and it screamed and smoked the belt. Pulley turns fine and independently of the clutch when disengaged. BUT the clutch turns fairly easily by hand. I bought (I think for the price of shipping) another compressor from a CO member last summer (off a '72 I think) and that clutch turns with about the same resistance. So I'm a little confused. Why would the AC frag and smoke the belt if I can turn the clutch by hand? How much resistance should I feel? Maybe it seizes after running for a few minutes?

Macadoo

Okay, my wrists hurt a little but I turned that sucker by hand for about three minutes solid and by golly, it did tighten up the more I turned it. Not extremely tight but enough to feel a good difference. My backup compressor, however, did not. I'm going to clean it up and install it and hope for the best.
Umm...unless that's what is supposed to do with pressure in the system?

MDchanic

I agree with you, Mac - it sounds like this compressor is shot.

I do not have experience with compressors tightening up in any organized way, but I did just (today) replace the compressor on my BMW because the old one did essentially the same thing - as it cycled at highway speeds, it felt like someone was applying and releasing the brake pedal, then, if you dropped down to idle, it'd pull down to about 400 RPM when the clutch kicked in. When I turned it by hand, it felt okay, but it was obvious that it was NOT okay.

We'll see if the new one fixes it.

- Eric

Macadoo

And that just shook loose a memory from last summer. When I first got the present compressor going, the belt on the input side was flapping around like a flag on the 4th of July. When I asked the fella at the shop that charged the system about it, he said "Oh, yeah, those old compressors will do that."

Question: after I replace the compressor with my backup, can I test it before charging the system or does it need to be charged before it would exhibit any problems? Or is it like modern compressors that won't engage when not charged?

MDchanic

I don't know of any way to test it without using it.

The general rule is pretty much that if there's any question about it, you rebuild it (which often doesn't work) or replace it.
I've never seen any guidelines for determining condition if the system is not working.

- Eric

Macadoo

Understood. I'll go with the "fingers crossed" method, then.

Macadoo

Any idea how much oil to add when replacing just the compressor?

MDchanic

No, but I believe they list approximate quantities in the CSM.

The A6 compressor has an oil sump with its own drain plug, so you add the oil there.

- Eric

Macadoo

That much I knew, thanks. What I can't find is the high-side service port. Now remember, I've already had the system converted to 134a and I see the retrofitted low side valve but not the high-side. Is it the brass cap on top of the hose-to-compressor fitting? If so, it doesn't appear to have a retrofitted valve. When the shop made the conversion and charged the system, they would have needed a gauge on the high-side port, yes? Could they have vacuumed from just the low side?

MDchanic

Well, yeah, they could have...

You said it was converted, not that it was converted correctly.
Shops do all sorts of things.

And, yes, the port should be on the compressor fitting.

Sounds like while you have the system open, you MAW...

- Eric

Macadoo

MAWWW.......

The only thing that wasn't done was calibration of the POA. 1/4 turn counter clockwise if I remember correctly.

MDchanic

Do it.

And flush the system if you're not sure whether anyone ever did.

You do have a parallel-flow condenser, and an 134-compatible receiver, right...?

- Eric

Macadoo

So, drain oil from old compressor, measure, add same to new compressor. And if nothing came out of the old compressor? From anywhere? Dry as a bone? Suspicious?

To answer your questions; yup, yup, and yup. I did everything last year, including flushing the system and having the evaporator pressure tested at a rad shop. I think I'm good to go.

Macadoo

Wait, that's a "no" on the condenser. But she was blowin' cold last summer before it seized. Hot weather too; 93* IIRC.

MDchanic

I hate when people take care of the MAWs ahead of time.


If it's cold enough for you, then that's fine.

The parallel-flow condensers shed a bit more heat than the serpentine condensers that these cars were originally equipped with, but if it works for you, that's all that matters.

- Eric

Fun71

Classic example of how "hot weather" means different things to different folks. It was low 90s on my drive to work at 8am this morning.

Macadoo

Well it's done but I don't think it's going to last long. I think this compressor is toast as well. A light clattering noise, like a loose piston and the input/push side of the belt is flapping around. It blows good and cold though, and I'll use it as long as it lasts. Had a heckeva time finding a high-side port adapter.
Since I had most of the 134a, oil, and compressor, all in I'm right around $40 so not a huge loss when it goes.
Kenneth, it's not the temp that'll get ya here in the plains but the humidity. It's been hanging around 95-100% for a couple of weeks now. But I'm not even going to try and compete with your temps out west.

Fun71

I lived on the Gulf Coast for 30 years, so I am quite familiar with humidity. We had it year round there - we often ran the AC on Thanksgiving, Christmas, and Easter. There's a reason why I live in the desert these days.

Macadoo

"Sure, it's 105 but it's a dry heat."
True, but that's still freakin' hot! Lol.

Fun71

105 would actually be quite nice compared to this:

Fun71

The above is why I don't drive my convertible in the summer.

Macadoo

Jeepers creepers!