Changing oil in a/c compressor on 88' S4

[911blex]

I am in the process of doing a R12 to R134a conversion on my 88' S4 which does not have rear a/c. I removed the a/c compressor today for the purpose of draining out the old mineral oil and replacing with PAG lubricant. My car has a Denso a/c compressor, which is different than the Bosch a/c compressor in my service manual. Could any of you please be so kind to tell me the following:

1. Other than turning the compressor upside down, is there anything I need to do to drain all of the old oil out?

2. Is it important to bring the compressor into a warm environment when draining it (i.e. my garage is very cold in Wisconsin)?

3. How many ounces of PAG lubricant should I put back into my compressor and where should I pour it into? My compressor doesn't have a fill plug like the Bosch compressor in the manual.

4. Should I replace the two schrader valves in the compressor?

5. Any other things I should do to the compressor before I reinstall it?

[911blex]

The last owner of my car did a partial R134a conversion that didn't work so I am redoing everything throughly with hopes that it will work better this time. I'd much rather have an R12 system.

[911blex]

Originally Posted by John Taylor

Some of the front compressor seals will not hold the 134, so even if the rest of your system is in good shape, it will leak through the front seal. Sometimes takes only a few weeks to lose a bunch of your 134 through the front seal. Make sure yours is 134-friendly if that's what you're going to use.

If you're redoing everything anyway, it would be just as easy to go back to the 12, which will do a better job of cooling than the 134.

My car now has a R134a expansion valve, will R12 work with this expansion valve. If not, can R12 expansion valves still be purchased?

Also, what lubricant would you suggest I use in my compressor if I decide to return the car to R12?

[dprantl]

Originally Posted by 911blex

I am in the process of doing a R12 to R134a conversion on my 88' S4 which does not have rear a/c. I removed the a/c compressor today for the purpose of draining out the old mineral oil and replacing with PAG lubricant. My car has a Denso a/c compressor, which is different than the Bosch a/c compressor in my service manual. Could any of you please be so kind to tell me the following:

1. Other than turning the compressor upside down, is there anything I need to do to drain all of the old oil out?

2. Is it important to bring the compressor into a warm environment when draining it (i.e. my garage is very cold in Wisconsin)?

3. How many ounces of PAG lubricant should I put back into my compressor and where should I pour it into? My compressor doesn't have a fill plug like the Bosch compressor in the manual.

4. Should I replace the two schrader valves in the compressor?

5. Any other things I should do to the compressor before I reinstall it?

Stop right now. Never put PAG oil into a system that had R12 mineral oil in it. There will always br traces of mineral oil even after multiple flushes of the system and mineral oil mixed with PAG is a really bad idea. You should be using ester oil only.

Your '88 S4 has the Nippondenso 6E171 compressor. Don't listen to people that say that the compressor "won't hold" R134a. Just replace the shaft seal and the body o-rings on each end and you will be fine. You may also want to check your A/C hoses for traces of oil to see if they are leaking, especially around the crimped ferrules.

Turning the compressor upside down should remove all the oil from it, it doesn't need to be in a warm environment; as long as the oil is coming out it's fine. You will also want to flush the evaporator and condenser out with mineral spirits using compressed air. To fill the compressor, I usually put everything together, then disconnect the low-side 90 degree fitting on the passenger side that goes down directly into the compressor, put a funnel on it and pour the oil in there. You should be putting in 300ml +/- 20ml.

Yes, you should replace the schrader valves because they will eventually fail. You cannot use standard tire valves, they must have seals designed for A/C systems. You will also want to replace all the o-rings in the system with nitrile (green) o-rings. Also, you will need a good quality vacuum pump (not one that connects to an air compressor) and pull a deep vacuum for at least 30 minutes.

[dprantl]

Originally Posted by John Taylor

Why change to 134?

Because it works well when converted properly and a 30lbs tank of R134a costs $95.

[Danglerb]

Advice I was given is do what the person that warranties the compressor tells you to do, and that was to use PAG after flush and evacuate on mine.

[dprantl]

Originally Posted by Danglerb

Advice I was given is do what the person that warranties the compressor tells you to do, and that was to use PAG after flush and evacuate on mine.

Interesting. I've done several conversions with ester oil with sanden and nippondenso compressors and have never had any problem. Every A/C specialist I've talked with said never to use PAG in a system that once had R12. My converted 928 has been working for years, I guess YMMV.

[dprantl]

Originally Posted by John Taylor

Guess it was more of a rhetorical question.

New cars designed to use 134 work well, blow ice cold. The same can not be said for a 134 conversion using stock 928 condenser, evaporator, etc. No matter how well done, it will never cool as well with 134 as it does with 12. Lots of 12 available at fairly cheap price on ebay and other sources. If done right, freon is a one time hit, and there's not the severe disparity in 12/134 pricing as there was a few years ago.

It is true that an R12 system converted to R134a without switching to a parallel-flow condenser does not cool as well. However, it cools just fine for me in summer at 100 deg F temps in stop/go traffic (if I put it on max, my passenger will tell me to turn it down after a while), so the performance drop is neglibile at least for me. Even after playing soccer outside for 1.5 hours at noon in that heat (and the car sitting in it uncovered), after a 15 minute ride it's like I was never outside.

As for the price disparity, R12 usually goes for at least 6 times the price of R134a. Sometimes I see people get lucky and get away with as low as 4 times the price, but that is pretty rare. I also see it coming up less and less on ebay. In fact, there aren't any 30lb tanks on ebay at all right now, but there are bunches of R134a 30lb tanks for as low as $59.

Also, thinking you can fix the system up and not have it leak for another 15 years is wishful thinking unless you replace absolutely everything with new and do the installation right. Even I've had some leaks and I've been doing A/C stuff for years (i.e. those damn schrader valves on the compressor )

[ROG100]

I can never understand why anyone with a 928 would want to convert to R134a when R12 is readily available and cheap. You can buy R12 at your local NAPA or Autozone for $20 a can. All you need is a Certificate which takes 15 mins and costs $20. On eBay you can buy it for $13 a can.
Do not listen to anyone who tells you R12 is hard to get as it is available right on your doorstep.
The 928 system was designed to use R12 until 1993. Even the early 93 GTS's were R12.
Stick with R12 and make sure your system is leak free and it will give you many years of no cost ice cold air.

[Pauwl]

Originally Posted by ROG100

I can never understand why anyone with a 928 would want to convert to R134a when R12 is readily available and cheap.

In Europe we're not allowed to use R12 anymore. We have no choice....
It's on my list of things I need to do...

[Danglerb]

If you live in AZ or FL, worry about it, otherwise don't. I told my AC guy, you pick the gas, cause you are going to be keeping it working.