'89 740

I undertook to retrofit my '89 744 with R-134, but decided to try to "do it right."

I am replacing the Diesel Kiki compressor (which I was told was rather inefficient compared to newer designs) with a Sanden SD7, as well as replacing all O-Rings, the accumulator, and the Orifice w/ a Variable Orifice.

The Sanden was labeled "R-12" so I emptied all of the presumably mineral oil from it by removing the bolt from the top, ans well as the rear caps, and pouring/rotating the compressor by hand. I got out about 3.5oz or so, but was hesitant to flush and rotate w/ A/C flush liquid for fear I couldn't get it all out, and that it could do harm. I added 4.25oz of Ester Oil, which is supposed to mix OK with mineral oil (unlike PAG oil), and is compatible w/ R-134.

I am NOT replacing the flex-hoses, and hope that they are in good shape, PLUS won't weep R134. I read that mineral oil exposure coats the hoses and provides a barrier to R134. We'll see. I know a lot of folks have said they successfully retrofitted R134 without even a new orifice, pressure switch, or even replacing all of the O-Rings, so I hope retaining the hoses won't be a problem. If they are, so be it, I guess.

I was told that the Sanden should bolt-right-in, which it does reasonably well. The mounting ears are similarly positioned. The threaded line fittings have the same threads, but they are angled (rather than parallel and vertical), which required very slight bending of the aluminum hard-lines to get them to thread-right-into the compressor straight. NO problem at all.

Unfortunately, the fittings are much closer to the mounting ears than w/ the D-K compressor, so the rear mounting plates could not be positioned as stock w/o preventing the lines from threading into the compressor.

That was solved by mounting the plates in FRONT of the rear compressor ears (rather than behind), as stock. That means that it will not align w/ the rear adjustment bracket. The solution is to space that bracket forward enough to engage the re-positioned plate.

The new compressor can be seen in the photo link:
http://screencast.com/t/LTEOv5LE
The labels point to what I mentioned in the text for reference.

Note the white wire, which is spliced to the compressor clutch wire. It will be used to activate a small DIN relay to cause the pusher fan in front to the condensor to run anytime the clutch is engaged, which should result in lower pressures, and greater cooling (I hope).

As you can see, it's an easy retrofit, and hopefully will be a worthwhile upgrade for the trouble (since my D-K operated smoothly, though I didn't pressure check it to make sure the seals were still good).

I plan to use Nylog Blue liberally on all O-Rings when I install them, as I understand it's "the way to go" for trouble-free operation.

So far the only "hitch" has been that removing the condensor to drain and blow-it-out (they said it cannot be properly cleaned in-place and will retain mineral oil in the lower tubes), I broke one of the rubber "motor mount" type mounting devices when the 10mm headed nut wouldn't come off easily.

The old orifice tube was pretty stubborn in the evaporator tube, and needle nose pliers wouldn't pull it out. Fortunately some duck-bill pliers had enough purchase to hold it tightly enough to remove it. I don't know WHAT one does if it is STUCK, or breaks in place. I don't even WANT to think about that!

Beside the new Variable Orifice, I am installing a higher pressure adjustable switch in the new accumulator (Receiver-drier). Not sure with the VOV (Variable Orifice Valve) I NEED a higher pressure switch, but since it's adjustable, hopefully it will be able to compensate in any case.

When I get the system evacuated, and re-charged I'll report how it works.

Thanks to those who offered info and encouragement to do this.

Any and all comments welcome, especially before I obtain the new O-Rings (I'm measuring them and matching them up at a dealer since no "list" of what I'd need could be found in advance) and button the system up and charge it.

Bob