a/c - where i start - PeachParts Mercedes-Benz Forum

blankenship · #1 05-16-2005, 07:35 PM

while i'm pretty good/experienced w/ other things on my cars, i've always been scared of the a/c system, and have never attempted to work on one.
to make matters worse, the haynes manual just says "take it to a pro" in the a/c chapter...

so, my '80 300TD won't blow cold, and i can't hear the compressor come on. i seem to remember that if you can't turn the front of the compressor by hand (is that the clutch?) that it's locked up and you need a new compressor + clutch...

is that right, and could it be as simple as that, or is there a way for a shadetree like me to know the condition of the evaporator core, accumulator, expansion valve, etc, and whether they should be replaced simultaneously?
add to that the fact that my current compressor shows R134 refrigerant? should i just shut up, and "take it to a pro" and drop what i'm imagining is $700 or so?

boneheaddoctor · #2 05-16-2005, 08:31 PM

try a search ...........you got major issues to consider doing it yourself if you have a locked up pump...and you need to know what all of them are...and it involves flushing all the components out properly.

blankenship · #3 05-16-2005, 09:01 PM

so, that is to say if i can't turn that end of the compressor by hand, i've got a "locked up pump?"

boneheaddoctor · #4 05-16-2005, 09:07 PM

Quote:

Originally Posted by blankenship

so, that is to say if i can't turn that end of the compressor by hand, i've got a "locked up pump?"

Are you trying to turn the pully part or the front part......I think the front part is stationary.......and is the clutch energizing.........it won't if charge is low.

if the pump is froze it has the "Black Death" any shortcuts taken with the system will dramaticly reduce the life of any new pump you put in it....as debris ends up all through the system. Which is the reason I suggested a search as you will need to read most of the vast info that has already been posted by some experts....this is a lot more involved than most other jobs.

rurik · #5 05-17-2005, 01:11 AM

Quote:

Originally Posted by blankenship

is that right, and could it be as simple as that, or is there a way for a shadetree like me to know the condition of the evaporator core, accumulator, expansion valve, etc, and whether they should be replaced simultaneously?
add to that the fact that my current compressor shows R134 refrigerant? should i just shut up, and "take it to a pro" and drop what i'm imagining is $700 or so?

well... i just went through the AC resuscitation process myself, starting with zero AC knowledge, to the point where I have (semi-)cold air blowing from the vents. I've no regrets over having done all this myself vs. taking it to the shop, but it took some time and some special tools. There's more than enough info on this forum to explain all common AC tasks. None of the AC repair jobs are too hard for DYI, really, with a notable exception of evaporator replacement (which would be a $2500 job if you let pros do it), but even that is a doable project, just very long and tedious. As far as MB jobs go, AC work is actually not bad as you don't need to pony up $$$ for special MB-only tools, and even parts are reasonably priced (for a MB). If you can borrow a vacuum pump off someone, AC work is downright cheap. About the only job you can't (while staying on the right side of the law and possibly your consciousness) do at home is evacuating refrigerant from the system -- you need a recycling machine for that. Sounds like it's one problem you won't have to deal with, though, you system is likely empty.

Your compressor may or may not be entirely dead. You'd need to be totally unable to rotate the front clutch plate on the compressor, which is awkward to get at with the belt in place, and it not easy to rotate even on an OK compressor (yours may devoid of oil, too). Try taking off the belt, so that you can try rotating the clutch plate together with the pulley.

Hit Man X · #6 05-17-2005, 01:21 AM

I've rebuilt two AC sytems in the past, they're just not that hard to do... but will take a while to do properly.

If your compressor is indeed seized, you'll need to flush the entire system from the current oil and this will get out any metal that's for sure in there too. A few places here charge $70-100 to flush an A/C system, money well spent to me as I just don't have the adapters to do so.

Installing new hoses, o-rings, dryer/accumulator, etc That's pie once you have it apart and the ref out (if any). Hit it with a vac, then charge it.

Eric Eliel · #7 05-17-2005, 11:59 AM

You need to "jump" the electrical circuit near the receiver/dryer. There are two "switches" that mount to the R/D. One is a low pressure cut out switch and the other is a temp fan switch that kicks on the aux fan in front of the radiator. You need to jump the low pressure cut out switch.

Run the engine, engage the a/c switch in the car (the middle one). If the compressor starts squealing-turn off immediately, you have a seized compressor. (Thats bad!)

If it doesn't start squealing AND the compressor engages, you are much better off. If nothing happens, you may have additional electrical gremlins you'll need to solve.

IMHO, you have a 24 yo car and the chance that the compressor is still good is slim. It may not be seized, but it probably leaks around the front shaft seal.

DO NOT INSTALL A REBUILT A/C COMPRESSOR. ONLY INSTALL A NEW AC DELCO COMPRESSOR.

Hit Man X · #8 05-17-2005, 07:47 PM

Quote:

Originally Posted by Eric Eliel

DO NOT INSTALL A REBUILT A/C COMPRESSOR. ONLY INSTALL A NEW AC DELCO COMPRESSOR.

I can't agree more, rebuilt compressors I stay away from... made that mistake once on my F150. It's already failing.

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