dprantl

1. The 6E171 should have a drain plug at the bottom.
2. I just install everything, then disconnect the low-side hose from the car and pour oil down the hose into the compressor.

Dan
'91 928GT S/C

JHowell37

I'll second the suggestion to go with the ester oil.

Big Dave

Yep.

Measuring how much comes out will be a problem...some of it is already out.

Where can I find out how much ester oil to fill with when switching to R134? Is too much a bad thing?

AO

Look at the GTS specs. They had factory fill with 134a, but I believe most had rear air.

Kevin in Atlanta

I used Brake Cleen to get all the R-12 oil out, did the same for condensor coil. When I swaped to 134 in my 86.5 I replaced the evaporator valves and dryer, too. If you have rear air I think you need more oil?

Don't forget to include some dye for spotting laeks.

dr bob

The WSM has the oil fill amounts by component for your car. Go with that recommendation. The deal with measuring the amount that comes out is that it gives you an idea of what needs to go back in if nothing else is changed, and is a minimum that should be put back in. When you buy a new or rebuilt compressor, the suppliers generally include a full-system charge of oil in it. If you are installing that compressor in a system that's already been operated, some of the original charge is now coating the walls of the condenser and evaporator, the linings in the hoses, and saturated the dessicant media in the drier. So you don't need that full system charge. When just reinstalling the old compressor as was mentioned, you really do want to know how much was in there and what it looks like, so I generally just drain the compressor into a little plastic measuring cup. Less than $2 at Wal-Mart for the set, and you can use them for lots of things, plus they can sneak into the dishwasher sometimes.

Anyway, you'll likely want to end up with somewhere around 6-8 ounces of oil in the used compressor. When you drain the old oil out, some will still cling to the internals, so it's likely you'll see less than the original charge amount in your measuring cup. If you do the drain-fill-drain-fill-drain-refill exercise I suggested above, it's more likely that the oil remaining will be new. How much oil to add in that last refill? I go with somewhere near what came out in the initial draining, maybe a bit more if I suspect that the system has been leaking a lot. It's a judgement call for sure. You generally want to err on the too-much side rather than too-little, but too much means that the oil film on the condenser and evaporator may be bigger/thicker. Unless you do a thorough flush of the system, including the compressor, then replace the drier with new, you won't need the full-system charge level of oil.

Clear as mud?

Big Dave

Actually quite clear!

Thanks!

JHowell37

Griffith's recommends 6-8 ounces.

Someone mentioned using brake cleaner to get the old oil out. I've been doing A LOT of reading on A/C systems this past week since mine has been giving me some ****, and I don't advise going that route. It's iffy whether or not brake cleaner is safe for the seals, and then you definitely have to make sure it's all out before you reinstall/recharge.

You should be good to fill the compressor, drain, and refill it.

I'm assuming you are planing to change out the drier? You really should. It's a bit of a PITA on a '85, but needs to be done. Just make sure you get the threads properly lined up

dprantl

Whatever you do, DON'T do that. The GTS (and all 90+) has a different compressor and has a very different compressor oil quantity. Off the top of my head it is somewhere around 300ml of ester oil for a 6E171, but please double-check this. There is also a Porsche publication that lists the percentages of oil in each part of the system.

And filling the compressor with too much oil is a very bad thing. It will coat mostly the interior evaporator surfaces and will greatly reduce the heat transfer away from the cabin.

Dan
'91 928GT S/C

Big Dave

Thanks for the advice. I do have a new drier.

Big Dave

Plans for the a/c are on hold. The used "working" compressor I purchased has a broken lower mount. There's nothing left to tension the belt. I'm working on a solution with the seller.

cfc928gt

Dave, you can buy the shaft seal kit from Arizona Mobile Air Inc., 800/648-4475. Part # 21-34609, it cost $19.48 shipped. My kit is sitting on my desk awaiting motivation...