A/C evaporator... to replace or not to replace?

[nmlss2006]

The car I'm presently working on is a 2/91 build - one of the last coupe E30s built. When the engine was swapped in early 2009 the PO elected to remove all the AC bits save for the evaporator, expansion valve and two lines that go from there to the engine bay. I was starting to remove everything when i found a GREEN seal at the 17mm nut into the valve. Should I stop, add the remaining pieces, pull a vacuum, put in R134a and live happily ever after? Should I take everything apart, flush the evaporator, replace the valve and all the O-rings and THEN live happily ever after?

[jlevie]

Remove and flush the evaporator and lines. Consider Freeze12 or similar rather that R134a if you want and A/C system that works close to like it did with R12.

[nmlss2006]

Why do you tell me things I do not want to hear? :) Getting the 21mm (?) nut out of there is going to be the most fun I've had in quite a while.

[jlevie]

The other option would be to try to come up with some way to flush the evaporator with it still in the car. My concern would be trash that got in with the lines open that could later plug the expansion valve.

That 21mm nut may surprise you. I had the same thoughts when I pulled the evaporator from my race car. But surprisingly it wasn't difficult to break loose.

[nmlss2006]

Yes, that's my concern also: the valve is delicate to start with and if I try flushing through it... disaster may happen. Is there a particular flushing shop/brand that you recommend? I educated myself on the how, but the specifics I've never had to deal with: do I just buy the $8.99 stuff from autozone and pour it in, slosh, wait 10 mins and pour it out? That seems... wishful thinking in a serpentine system.
Edit: further research seems to strongly favour buying the stuff from NAPA, pouring in, blowing out with compressed air, repeating 3-4 times. I wonder if, given all this, acetone will work? It will leave no residue, it's one of the most aggressive apolar solvents that I care to use outside of a lab and I happen to have two half-gallons downstairs.

[jlevie]

That should work. Turn the evaporator through every angle while to flush is in it. Then drain it and blow it out with clean compressed air.

[nmlss2006]

I looked at the MSDS for the Dura II at NAPA. The stuff they sell is a LOT milder. Something tells me I'll try that first. Now to get to that third torx screw again... sigh.

[nmlss2006]

Now comes the $999,999,999 question: let's say I flush everything lovingly and change all the O-rings. If I am to use Freeze12 (which given my experience with R134a in an E30 I am more than ready to try)... which expansion valve do I use? The old R12 valve or a new R-134a valve?

[jlevie]

Use the R12 valve. Freeze12 has nearly the same thermodynamic characteristics as R12, which is why it works better in a system sized for R12. Since everything has been open for a while, I think I'd get a new expansion valve. And I'd use new (green) o-rings everywhere.

[nmlss2006]

Yes see, there's the problem: you can't get a new R12 valve for love nor money: the new ones are R-134. But, we agree on the fact that R12 would work better... so I don't know what to do.

[nmlss2006]

The whole assembly came out. That nut is not repeat not coming loose. Neither are the two that hold the valve to the evaporator. The tubes to the evaporator are copper: I already bent them several times trying to get the parts out. I suppose one way would be to put the valve assy in a bench vise and go to town, but I am leaning towards buying everything new.
For reference, btw, there were *3/91* dates on everything and the hose certainly looks like barrier hose to me: did the 1991 build cars leave with R134a from the factory?
Edit: by the by, anyone who tells you that the assembly, with or without the pipes, 'just slides out' is a liar. If you remove the beige insulation AND remove all the DME wiring AND swear at it in four languages (I'm so cosmopolitan!) for 10 minutes straight, THEN you can get the evaporator out with a significant amount of bent fins. If it didn't have a leak before, it certainly does now.