Hilton

Just in case you manage to get hold of some cheap digital scales..

In my experience weight is reliable.. once you figure out the Porsche r134a conversion tech bulletin is wrong on the weight for 134a in pre-1990 cars The tech bulletin says 860g - same as it says for the 10PA20C cars, despite the much larger compressor volume of the 6E171.

For cars with the 6E171 compressor, running r134a:

front AC only: 950g r134a
300ml +/- 20ml PAG/POE oil

alabbasi

I've not read all of the thread so i hope that I'm not repeating what someone else is saying.

The sight glass does not work with R134.It really does not work with R12 either as you can quite easily over charge the system by looking at the sight glass.

As a general rule for my cars (mostly Mercedes). I look for 30-40psi on the low side and 2-2.5 times the outside temp on the high side (so if it's 100 degrees, I would expect to see around 200-250psi).

If you're pulling a vacuum, then charge the system by weight as you know that nothing is in there. In this case, you should be aiming for about 80% of what the sticker on the hood says the charging weight should be.

This is because R134 runs at a higher pressure then R12 and therefore you charge with less volume in order to maintain the similar pressures.

Rob Edwards

Why not just get a cheap digital scale and skip all the guesswork? Then you can weigh stuff, too.

http://www.ebay.com/itm/86-LB-DIGITA...item2570d81a11

WallyP

If the system has ever been charged with R-12 and mineral oil, never use PAG - it is not compatible at all with even remnants of mineral oil.

POE will work fine, and does tolerate mineral oil.

High side pressures are affected by cooling air flow over the condenser much more than by the amount of refrigerant in the system. Weight is the only practical way to measure the charge.

Speedtoys

Ya..I went with weight..but its still a guess, because I dont have the full rear AC plumbed in..its blocked at the low side under the car at the line connection (not the connection INTO the car, but up the frame rail).

Ive got the Expansive valve into the low 40s before my last 12oz can ran out..so im close..and for now, done.

Will dive in and plumb back in the rear A/C, replace the dryer, and get a Pflow condenser here in a few weeks.

Who has the current well-sized for fitment Pflow condenser these days for sale?

fraggle

Pflow? Is that a replacement from stock? I found my rear lines are leaking inside the car... I'll need to rebuild or replace.

SQLGuy

Pflow probably means parallel flow, which would be a change from stock.

There are four places in and under the car where there are O-rings for the rear lines:

1. Just forwards of the back edge of the rear undertray.
2. Under the car where the hoses connect to the flange that brings the lines through the floor under the passenger seat.
3. At the solenoid under the passenger seat.
4. At the rear expansion valve, which is in the "hump" at the forward end of the rear evaporator.

Besides these, the rear evaporator itself has been known to develop leaks where the copper lines of the "squid" are pressed into the aluminum of the evaporator itself. I had good luck cleaning these connections and then sealing them with Muggy Weld Super Alloy 1 solder. Others have reported good experience sealing the connections with aircraft grade epoxies (search for rear A/C threads).

fraggle

Thanks for that info! Myrear lines seem to be leaking from the crimp about 8" away from the rear expansion valve. There's dye everywhere under the carpet. I don't think this is going to be any fun to replace.

dprantl

The aftermarket parallel flow condenser is only a direct replacement for a S4+ 928 with the 5-speed condenser which is taller than the version in automatics. I believe the 5-speed GTSes also have the shorter condenser due to the manual transmission cooler.

Dan
'91 928GT S/C 475hp/460lb.ft

Speedtoys

Well that sucks.

dr bob

Plugging just the suction side to the rear unit means that eventually the whole rear system will be at high-side pressures. And will leak.

Speedtoys

If it didnt leak before, why would it leak now?

The solenoid isnt being opened for it.

dprantl

Well, if the rear A/C solenoid doesn't perfectly seal internally (which I think it doesn't really have to in a properly functioning system), if you run the system long enough, the high side will pressurize the low side. When that happens, the low side components will have more pressure in them than they were designed to handle, and will spring leaks. I'm not sure how likely that is, but it is a possibility.

Dan
'91 928GT S/C 475hp/460lb.ft

Tom. M

The parallel flow one I got is shorter than the stock one was..I"ll take a pic and some measurements when I get home. Maybe it will be short enough for the AT cooler equipped cars?

fraggle

My replacement was also the short style, I put it in anyway - it bolts together just fine.