A few A/C questions - PeachParts Mercedes-Benz Forum

donbryce · #1 02-27-2008, 08:05 PM

I'm in the middle of a winter overhaul, and working on the A/C system ('86 560SL). PO said it had not been working for many years, and I noticed when I bought the car that the compressor drive belt was missing. All related pulleys had rusty grooves.

Compressor (nippondesso)
I removed the compressor, shimmed the pulley, cleaned up the clutch, and verified it works. Local shop says no way to test compression until it's on the car and the system is charged, which will be 134A. Ports look clean, it spins freely with no noticable noise.
The mechanic mentioned, however, that the seals go bad if a compressor sits on the shelf too long, which is why I should not trust aftermarket 'rebuilt' units, and they don't rebuild them either.
>> Fact or fiction? Should I just get a new one, given the amount of time it's been idle, to avoid contaminating the whole system?

Hoses
I tested the main hose assembly, attached to the compressor, by plugging the ends and immersing it in water under 100lbs air pressure. No bubbles. The line from the dryer to the expansion valve had a cracked-in-two-pieces nut that I replaced with one from the old dryer. Had to cut the aluminum line and use a Swagelok union.
There is a minute residue of rust inside the end of this line fitting, where it attaches to the expansion valve, and rust inside the old dryer and parts of the main line. I blew brake cleaner through both (recommended by indie) and air dried.
>>Will some minor rust residue, from I assume the system being empty so long, be OK after I button everything up and get it vacuumed/nitrogen tested/charged?

Receiver/Dryer & Condenser
Both new. Condenser is OEM Behr. I'll wait until last minute to finalize install, to avoid contamination.
>>Can I expect good performance with 134A?

Evaporator Expansion Valve
On the advice of the indie, I'm planning to 'clean' it with the can of brake cleaner he recommended (leaves no residue) and air-blowdry, with the valve removed. I'll buy a new expansion valve.
Edit: Took off the valve today. Fairly easy, except for the clip that holds the temp. sensor coil on the evaporator pipe. An hour! Damn thing is TIGHT and no room to manouvre. Finally got it off with a pair of brake drum shoe spring pliers. Nice to finally use these after 20 years.
>>Should I buy some acetone instead or in addition and run some through it with my engine cleaning wand hooked to air compressor, or just do the brake cleaner?

I'm going to order a complete R12 to 134A conversion kit. Where I live, if we get 30 days of A/C worthy weather a year, we're lucky, so I'm OK with reduced efficiency, as discussed here, but I won't know what I've got until it's all said and done and into the shop for the charge-up.
>>Am I on the right track.....missing anything critical?

mbdoc · #2 02-28-2008, 08:47 AM

Don't use brake system cleaner...use A/C system flush.

Don't open the drier untill you are ready to pull vacuum on the system.

Randy · #3 02-28-2008, 12:14 PM

The seal on the compressor is replacable I think. If there is no evidence of Black Death in the system it might be good otherwise. Hope this helps you.

donbryce · #4 02-28-2008, 06:58 PM

Thanks to you both for the replies. There's a fair amount of controversy here on the right stuff for cleaning, and I'm certianly not gonna challenge the experts! I'll use approved A/C flush, IF I can find it locally, since aerosols/liquids can't be mailed. If not, any caveats on acetone?
I read up on 'black death', and so far, just finding powdery rust-like deposits. One port on the expansion valve was whistle-clean, even a trace of oil left, but the screen/filter port was totally gundged with brown residue. A new valve will definately be ordered.