Barnfind 300D - Recharging A/C - PeachParts Mercedes-Benz Forum

awt356 · #1 04-21-2011, 04:42 PM

I'm looking for some guidance in recharging the R-12 A/C system in my "new" 82 300D. The car only has 78k miles, but has been sitting in a garage since 1999. My manifold gauge set reads 9 psig when connected to the suction side(engine off). I assume the charge leaked out over the last 11 years. I momentarily jumped the low pressure switch wires to confirm that the compressor would engage. I have two 12oz can of R-12 available. Should I:
1. Add the R-12 that I have and hope for the best
2. Evacuate the system ... Then flush and replace compressor, expansion valve, dryer, etc., then recharge with R-12.
3. Something between 1 and 2

Thanks in advance

winmutt · #2 04-21-2011, 05:06 PM

#2.

leathermang · #3 04-21-2011, 05:36 PM

Second #2.

Yak · #4 04-21-2011, 08:24 PM

I vote for #3.

"Assume" and "hope" are not good ideas on the A/C.

Inspect everything first. Maybe a new R/D (only ~$20). Inspect your monovalve (don't want to dump heat into your heater core when the A/C is on). Check your vac pod operation for the flaps. Check the vac system in general.

O-ring kits are pretty cheap.

leathermang · #5 04-21-2011, 08:44 PM

I went with number two because our systems are meant to be run ... the recommendations even include turning on the AC in the winter to lube the front seal on the compressor... a designed ' leak' is built in to carry some oil to that front shaft seal..
sitting for ten years not being used at all.... and being low on refrigerant....
I hated to risk wasting that R12 he has... will is about 2/3rds what he will need... the Receiver dryer needs to be replaced.. meaning an unknown amount of the total oil charge is coming out...
I just think for a long lasting ( 6-8 ) years with no problems or servicing typically... that #2 was the best choice...

Yak · #6 04-21-2011, 09:29 PM

I think it all depends on what the "etc" in #2 is and what the comfort level on replacing parts and/or rebuilding is.

Maybe more than #2 with some hose replacement added in; maybe less with not replacing the compressor and only R&R'ing the clutch and a seal a la Funola's writeup from last summer.

I'll assume (against my own advice) that since the OP has cans of R12 and has a manifold gauge that fit and appears to know how to use it, that he knows he has R12 fittings and the system doesn't appear to have been converted to 134.

So, yeah, don't just put the R12 in and hope. But don't assume a specific list of parts yet either.

For example, I'm no expert but I've read that the expansion valves should match the refrigerant used for optimum operation. I don't think they make R12 TXV's anymore, so a new one would be R-134a. Is it enough to make a difference? I don't know and probably not, but if the existing valve is okay, maybe just new o-rings. (Some good theory on the TXV here: http://yarchive.net/ac/expansion_valve.html)

There's the difference in the sump/oil well/X-thing on older M-B compressors and new R-4 replacements since M-B compressors are upside down. Again, a significant difference? Maybe not. CompressorWorks says their 'new/updated' R-4 compressor doesn't need the extra lube; but anecdotal reports of Four Seasons compressors says they fail early because of this.

The OP's post count is low, so he may not be aware of the wealth of info and peculiarities of some of the W123 A/C components.

Do a little research, inspect the system and be prepared to go for #2 - or even more. Leak check - vacuum and pressure - have a plan to recover the R12 BEFORE putting it in, just in case, then go from there.

leathermang · #7 04-21-2011, 09:33 PM

Yak, it will not take the OP more than a couple of hundred hours to read the AC WAR threads... LOL