AC compressor seized? - Page 2 - PeachParts Mercedes-Benz Forum

vwnate1 · #16 12-24-2021, 03:18 PM

I was a Fleet Mechanic back when DELCO R4 compressors were standard fitment .

They're *very* good but s Bill mentions : they need proper service, I replaced a lot of the original ceramic seals when they were new, an easy job but no one ever bothered to replace the gone missing (leaked out) oil because that's time consuming .

I had no issues with the R4 compressor on my 1982 240D but wanted colder A/C so I went with Rich's first generation SANDEN kit, I used the 7 series compressor because I have experience that anything not the biggest and best in A/C means poor A/C out the dash registers .

As to what R4 compressor to buy, there are myriad part numbers, not all interchange and don't EVER buy a 'rebuilt' R4 compressor .

Jarod · #17 12-24-2021, 03:29 PM

Maybe someone can chime in to confirm or deny that I saw certain R4 compressors made for GM applications mount in a different orientation than the R4 on our cars do.

There is an oiling hole on the front bearing/seal that would normally be facing down, but due to the difference in mounting, getting the wrong one would have that port facing up, and the front seal would not get lube/cooled by the oil which tends to lead to premature seal failure (I've had 3 or 4 R4 compressors that all died from front seal failure despite being charged with the proper amount of the correct type of oil)

Am I insane, did I dream that or is there some deal with the front seal having a different orientation on the MB R4 compressors vs the ones assembled with GM cars in mind?

ROLLGUY · #18 12-26-2021, 07:50 PM

Quote:

Originally Posted by Jarod

Maybe someone can chime in to confirm or deny that I saw certain R4 compressors made for GM applications mount in a different orientation than the R4 on our cars do.

There is an oiling hole on the front bearing/seal that would normally be facing down, but due to the difference in mounting, getting the wrong one would have that port facing up, and the front seal would not get lube/cooled by the oil which tends to lead to premature seal failure (I've had 3 or 4 R4 compressors that all died from front seal failure despite being charged with the proper amount of the correct type of oil)

Am I insane, did I dream that or is there some deal with the front seal having a different orientation on the MB R4 compressors vs the ones assembled with GM cars in mind?

You are ABSOLUTELY correct! This is why many rebuilds fail in our cars. You can't even buy a new one that isn't made with Chinese parts (Compressorworks?). Another reason to shy away from any and all R4's.

BillGrissom · #19 12-28-2021, 03:34 PM

Sherm, the Sanden compressors are probably slightly better than R4. I think they have a swash-plate drive, like the Denso I took apart from my Plymouth. The 7-piston SD7 are newer and preferred. Double-acting, so essentially 14- pistons for a smooth output. I recall the R4 has a crankshaft w connecting rods and 5 pistons, single-acting. My Denso failed when the black anodizing wore off the aluminum pistons, to seize one in the aluminum bore. I think R4's can fail similarly.

ROLLGUY · #20 12-28-2021, 10:35 PM

Quote:

Originally Posted by BillGrissom

Sherm, the Sanden compressors are probably slightly better than R4. I think they have a swash-plate drive, like the Denso I took apart from my Plymouth. The 7-piston SD7 are newer and preferred. Double-acting, so essentially 14- pistons for a smooth output. I recall the R4 has a crankshaft w connecting rods and 5 pistons, single-acting. My Denso failed when the black anodizing wore off the aluminum pistons, to seize one in the aluminum bore. I think R4's can fail similarly.

R4 is a "Radial" 4 piston compressor, thus the R4 designation. It's GM predecessor was an "A6" meaning Axial, and 6 piston (actually 3 double acting=6). The Denso is in fact a similar design as the Sanden. Both are excellent compressors.

BillGrissom · #21 12-30-2021, 12:13 PM

Quote:

Originally Posted by ROLLGUY

R4 is a "Radial" 4 piston compressor, thus the R4 designation...

Thanks for clarifying. I should have remembered since I now recall taking a failed R4 apart long ago to see, and to scrap the aluminum "block". It was likely the one where the clutch slipped and smoked, and perhaps a piston seized in a bore, as in my Denso. I just recall it happened on a very hot day (which Rollguy also experiences). The main thing is that it has no oil sump, so relies on oil circulating in the system. At least in our cars, the R4 is down low where oil tends to stay.