I should have known better than to try to bring the GM R4 compressor back to life - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 06-29-2015, 02:31 PM

A couple weeks ago my brothers '85 300D threw the A/C belt, and he asked me to fix it. I told him the cost for a Sanden retrofit, but decided to try and save him some money by trying to resurrect the R4. It was replaced a while back, but the system had a leak that we could not find. He kept on adding 134a until it threw the belt. The compressor was not frozen, so I put a new belt on it and took it to the A/C shop to get leak checked and recharged. We found a bunch of small pinhole leaks in the low side hose going into the cabin. I went back home and made up and replaced that hose. Back to the shop and the system checked out leak free and was charged. It worked fine (with the exception of a bad Klima relay, so the compressor was hot-wired) for the next week or so. Fast forward to Friday, when his wife was driving it on the freeway when she heard a VERY LOUD BANG and HISS. Thinking she had a blowout, she prepared for a ride. When nothing happened but the cold air quitting, she proceeded on. After getting home and telling my bro' about it, he investigated it. Upon opening the hood he observed green oil everywhere in the vicinity of the compressor. This is what he found:

It appears that the case of the R4 exploded. Trying to figure out what caused it, we came up with a few ideas. It could have been excess pressure from the condenser fan quitting, or something like that. The other thing that I thought of is that it may have blown up from too much oil in the system, and the compressor was compressing more oil than refrigerant. The hose that was bad did not look oily in the least. I suspect that every time the system was charged, more oil was added. The leaks in the hose were not large enough to let oil out, but only refrigerant. Whatever the cause, I am NEVER going to work on another R4 again! It is just not worth the money and effort to get these compressors to work. At least that has been my experience. I should have bit the bullet and just put a Sanden in for him. Yes he would have not liked the extra expense, but he would have working A/C now!......Rich

BillGrissom · #2 06-29-2015, 03:05 PM

Sounds like not much was lost in trying. You still have the new suction hose you installed (just blow it out). I tried the R4 that came in my 1984 300D and it is still working fine. It had no refrigerant when I got it, so I sucked it down, installed ~4 oz mineral oil, and 2 cans of Duracool and has worked fine for several years.

When you change to a Sanden, you can re-use the factory R4 hose fitting. The tubes just need to be bent slightly to clear. I did so in my 1985, as did another guy. I swapped Sanden heads to one w/ "GM Pad" ports. I bent the tube on the car (w/ big pipe wrenches), but if again, I would remove it and replace the rubber hoses, running the H.P. hose straight to the condenser. I later did that on my 1985 when the hoses leaked. The hose kit you offer/offered did the same. Silly that M-B ran that hose up the R side of the engine.

Rogviler · #3 06-29-2015, 04:45 PM

Looking through the records for my car and how many times it needed to be replaced (and still the compressor was seized when I got it), it's definitely hard to have any faith in them.

-Rog

ROLLGUY · #4 06-29-2015, 05:10 PM

Quote:

Originally Posted by BillGrissom

Sounds like not much was lost in trying. You still have the new suction hose you installed (just blow it out).

Yes the hose needed replacing anyway, but the labor and refrigerant was lost. That equals out to about $150 that could have gone towards the Sanden. Oh well, I learned my lesson the hard way. I may have to give my bro' some labor to make up for it when I actually do the Sanden retrofit on his car.....Rich

vstech · #5 06-29-2015, 05:28 PM

Ya know, I didn't need to see the pic, I knew exactly what it was going to look like from the description...

ROLLGUY · #6 06-29-2015, 07:18 PM

Quote:

Originally Posted by vstech

Ya know, I didn't need to see the pic, I knew exactly what it was going to look like from the description...

Then you know exactly what caused it right? Not that I care anyway, as I have no desire to touch another R4 except to remove it. I even have a couple known good compressors that were removed, but they are not destined for anything but the scrap pile. I would not wish one of them on anyone.

vstech · #7 06-29-2015, 07:25 PM

Yup. Combination of too much oil, r134 high pressures and poor case mount design. If the rear line mount bolt is not present, the sleeve slides off.

Whiskeydan · #8 06-29-2015, 07:44 PM

I've found the reliability of R4 compressors is all over the place. I have one on a '85 SD that has very cold AC and has been running for years. Yet, it has a shaft seal leak that requires topping off every now and then. I have another new R4 but I am hesitant to replace this one that runs so quiet and well.
Then on the '84 SD I went thru three R4s before I installed a Sanden. Other than tightening the belt it's been flawless for two or three years now.

Both are running R152 btw.

vstech · #9 06-29-2015, 08:17 PM

? 152?

Partscarver · #10 06-29-2015, 08:34 PM

http://www.sae.org/altrefrigerant/presentations/presw-hill.pdf

97 SL320 · #11 06-29-2015, 09:31 PM

And how this is the fault of a compressor not originally designed to run on 134A, possibly overcharged with oil / freon , ( RE kept adding freon until the belt came off ) condenser fan not working, maybe outer can not captured properly.

Also no matter the type of compressor, if overcharged the suction side will experience "slugging" where liquid enter the suction side and will damage the compressor.

I worked on these when every GM and some imports used this compressor and never had one come apart like that. They were not the greatest compressor due to being designed like a 2 cycle engine making them less tolerant to low oil levels but did work well enough.

vstech · #12 06-30-2015, 08:20 AM

Yup, it's the mounting that makes them suck in MB vehicles. .. I've seen a LOT of them pop apart like that...

mach4 · #13 06-30-2015, 09:23 AM

Quote:

Originally Posted by vstech

Yup, it's the mounting that makes them suck in MB vehicles. .. I've seen a LOT of them pop apart like that...

Can you elaborate? I'm having trouble figuring out how a mount makes them come apart.

charmalu · #14 06-30-2015, 10:10 AM

There is this tiny little warning on each page.

WARNING: HFC-152a is a flammable refrigerant and should

not be used in systems unless specifically designed for its use.

My bro in Law is a commercial AC guy, I`ll send him the link.

He told me about some new stuff to replace 134a, maybe this is it.

Rich....ya shuda known bedder.

Charlie

ROLLGUY · #15 06-30-2015, 10:28 AM

Quote:

Originally Posted by charmalu

Rich....ya shuda known bedder.

Charlie

Yes I shuda, but I dint. I doo na!