'86 420SEL: Climate Control Time - PeachParts Mercedes-Benz Forum

Randy · #1 05-07-2009, 03:25 PM

Hi, I am repairing my CC: compressor seal leaks, etc. I noticed a previous tech installed a low-pressure R-134A test fitting in the high-pressure side. I intend to replace this with the correct high-pressure fitting while it is apart; anyone know a part that will work (i.e. fittings are correct)? Car had been converted before I got it and the CC works OK but the gas won't stay in it long and it is obviously leaking out the compressor seal.
Also, sometimes when tooling along in Cool mode, it would suddenly switch to hot. Maybe the evap temp sensor? What do you think?

TX76513 · #2 05-07-2009, 03:43 PM

Oddly enough my SD was configured the same when I purchased it. I believe it was a 16mm fitting but use THIS guide to help you figure it out. Pictures are always cool!

On the issue of heat - check you mono valve -

Hit Man X · #3 05-08-2009, 08:15 PM

If you're going to take the system apart, revert back to R12. It just cools far better in these cars.

The climate headunit itself could be going bad too, happens often. Check in the used market for a good reman from Beckmann or Programma.

Randy · #4 05-11-2009, 10:22 AM

HitMan, please describe what should be changed to reinstall R-12, as I am about to do something. Obviously test fittings; what else?
I do not know what was done to convert it (PO had it done and was not exactly a techie). I have ordered a new compressor and drier.
I do have an R-12 license.

Hit Man X · #5 05-11-2009, 08:46 PM

If the PO just slapped it together to work, I'd break open the system and flush it well. No telling what oil concoction is in there now... this includes flushing the evap core. NOT FUN, but it will get the system clean and operating properly. You will need some Crows-feet to remove the old expansion valve, a case of beer, and your patience. This is the worst part of the job by far.

I use Acetone for flush, cheaper than "AC Flush" and dries with no film.

Since new dryer is coming, order up new pressure and aux fan switches for the dryer too. ACkits.com for your o-ring pack (NYLOG), they're about $10? Also they have this snot looking stuff to hold orings in place and helps seal threads, it's worth it too.

I 100% advise removing the AC condenser itself and cleaning the fins out of the crap built up over the past 25 years. Leaves, bugs, rocks, etc. This all hampers its ability to shed heat, so with it clean it works that much better.

System oil is 8oz capacity, put most in the dryer (4-5oz) and fill the rest elsewhere. I put an ounce or so in the low pressure hose and the same in the high side. Then you're pretty much good to go.

Verify your fan clutch works right, this pulls air at low speeds. I'd probably go ahead and replace the fan belts since the compressor will be out.

R12 capacity is just shy of 3lbs (2.9lb I think) so I'd pick some up. I have enough old junk that I just bought a few 30lb tanks a while back. I'd look local if you have a Craigslist to get a case (ebay gets spendy as you have morons on there all the time) You will need about four, 12oz cans to fill the system properly.

That's basically it. Good weekend project if you work in a timely fashion.

Don't forget about the M116 V8 timing chain guides that like to break on your motor. Meyle has replacements that are aluminum backed so they won't fail.

Put the effort in (and keep it maintained) and you'll have a great ride once up to par!

Randy · #6 05-12-2009, 12:27 PM

Thanks a bunch for the info. I know my system has some sort of UV dye in it, to help locate leaks, there is a sticker on the radiator support, and I see the green stuff leak out of the compressor seal. I also know that: the high-side test fitting is the wrong one; they used a low-side fitting. The system will cool if it has gas in it, the gas just won't stay long. Radiator fan clutch and electric fan are good, don't know about the fan control switch and pressure switch; will buy new ones. I also may need an evaporator temp sensor.
BTW: I did the timing chain and guides a couple of years ago. Mine were yellowed, but not cracked but my chain was at the limit of 7 degrees. Also replaced the tensioner with an OEM, replaced plastic fittings on the cam oiler tubes, everything I could find to replace on this forum, I did. Thanks to everyone for the info. Maybe I'll finally be cool