[maddog2020]

I'm switching out my metal AC lines in the engine bay, (final part of removing the rear AC) and thought, it would be a good time to clean and possibly insulate the larger AC line. Porsche insulated the fuel cooler portion of this line which is all crumbly, and I thought I'd go ahead and redo that, but it also got me to thinking about insulating the rest of that line as it resides in a pretty hot area, and if it can improve the efficiency, even just a bit, it would be worth it. anyone else gone this route?

[worf]

I'm switching out my metal AC lines in the engine bay, (final part of removing the rear AC) and thought, it would be a good time to clean and possibly insulate the larger AC line. Porsche insulated the fuel cooler portion of this line which is all crumbly, and I thought I'd go ahead and redo that, but it also got me to thinking about insulating the rest of that line as it resides in a pretty hot area, and if it can improve the efficiency, even just a bit, it would be worth it. anyone else gone this route?

Seems like a good idea. The insulation is just the ‘floppy’ refridge-line stuff you can get at any good hardware store.

If the line is on a bench… go for it. I think I’ll copy you.

Did you buy new no-rear-AC lines? Or did you cut and plug the originals?

[worf]

Nevermind. I see you wrote “switching” so you bought new lines.

[maddog2020]

The larger line was available from 928intl and was in almost new condition. The other line was not available from Porsche and another Porsche salvage ruined 2 of the non rear air lines removing them and shipping them. I ended up buying the one I have from a place on eBay from Germany. Most of the S4 and later cars in the US have rear air so they are hard to come by. Knowing what I know now, I would just take the ones off the car and have them patched. They are made from aluminum and have some sort of grey anodizing on them. You will have to cut off the part of the lines that go under the car if you want to get them out of the car with an engine in place. Not a problem since you plan to have them patched. I would remove all of the t that goes to the rear and have someone weld or braise on a small round piece to patch the pipe. I would not just put a cap on a section of the T as that would provide a place for foreign debris to collect and you’d never get it out.

[maddog2020]

I also found that it is a bad idea to insulate this as it is a return line, and by insulating it you could cause the Freon to “slug” the compressor and cause more problems than you solve.

[worf]

You will have to ...

Dude, I removed my rear A/C 15 years ago. I have my own methods for doing that with the OE lines. One, reversible, method I've done to a few clients' 928s with leaking rear evaps.

I have new front-only A/C lines in storage that I'll put in when the motor's out for its '35-year' maintenance.

[worf]

I also found that it is a bad idea to insulate this as it is a return line, and by insulating it you could cause the Freon to “slug” the compressor and cause more problems than you solve.

Hmmm...

https://www.engineeringtoolbox.com/dich ... d_972.html

A healthy ND 10PA20 or 6E171 low side pressure is 1.5(-ish) to 2 BAR. Seems like it operates right on the saturation pressure line anyway.

But, no matter, if anecdotes exist that insulating the return line is potentially a bad thing then it should be approached with more thought.

In any case, the 928 is condenser limited.

[maddog2020]

got the condenser, engine bay and under car lines removed this evening. drained almost 8 ounces from the lines which ironically is the required amount of oil for a new compressor. it was foul smelling but clear and clean, so that was good. I'm convinced that this rear air design is why 928's eat compressors. if you don't run the rear air every time you run the front air, oil can and does pool in those lower lines. removing the rear air eliminates 10 different places the system can leak from. I'll have to remove my rear seat delete again to get the rear evaporator out.

[worf]

Sterling, replacement insulation for the fuel cooler (and the high-pressure line that goes "around" the radiator) can be found at any good hardware store. Go to where the 'normal' hard Styrofoam-type pipe insulation is stocked and you should find the the "squishy" EPDM-type foam for high-temp lines too. Two different sizes needed if you're doing both the cooler and high-pressure line. (New factory line I have has it already.)

I'm convinced that this rear air design is why 928's eat compressors. if you don't run the rear air every time you run the front air, oil can and does pool in those lower lines.

Pooling of the oil in the under-car lines is one factor. However, I think a bigger factor is "topping off" the refrigerant charge without adding oil.

I have seen that phenomenon reflected in numerous service record histories. It's especially visible in since-new factory-r-134a GTS histories where the charge leaked out every 2 to 3 years. What you see is two top-offs and then a compressor replacement.

removing the rear air eliminates 10 different places the system can leak from. I'll have to remove my rear seat delete again to get the rear evaporator out.

4 under-car o-rings
2 valve o-rings
4 expansion valve o-rings
1 valve
1 expansion valve
1 evaporator
2 hoses

15 places for it to leak.