Help an A/C Newb - 1982 240D - PeachParts Mercedes-Benz Forum

Sulawesi · #1 07-06-2010, 07:32 AM

I know there are many A/C threads, especially this time of year, but I have had trouble finding a good starting point.

I have a beautifully maintained 82 240D, that when I bought, the 22yr 2nd owner said that all the system needed was a charge. Of course, I did not believe that, but the way this car is, it may very well be the truth. I am open to the possibility, but also know it might be a project.

So where do I start? I have been searching the DIYs but am not really sure what I need, a test, a recharge, are there simple things to tell if the electrical and compression systems are working before testing the pressure etc?

Thanks for any links you can provide regarding initial diagnostics.

dannym · #2 07-06-2010, 08:15 AM

What refrigerant is in the system?

You really need pressure gauges if you want to do AC work yourself.

vstech · #3 07-06-2010, 08:39 AM

many parts of the system will not work if the charge is not at least close. I'd go to an auto parts store and pick up a set of gauges. unless you already know, I'd take a picture of the a/c lines and post it here so we can tell if you have 12 or 134 in the system. after you get pressures, post them here too and we'll tell if it's low/empty/fine, and we can go from there.
another place for gauges is a pawn shop, but it's unlikely you'd get 134 adapters with them. (hopefully you don't need adapters!!!)

leathermang · #4 07-06-2010, 09:31 AM

Quote:

Originally Posted by Sulawesi

... that when I bought, the 22yr 2nd owner said that all the system needed was a charge. .

I am glad you did not take that a face value... that is the classic statement ( and I am sure HOPE ) of all seller's with non working AC systems.
It is as common as a DUI suspect in a car telling how many beers he or she just had ( TWO !!! ) LOL

Follow vstech's instructions and we will get you going towards a logical and hopefully frugal correction of your AC system. Report back often with results of tests, ask questions if you do not fully understand anything... and WEAR GOGGLEs when working on AC systems...

Sulawesi · #5 07-06-2010, 09:48 AM

I am going to assume it is R12 because the car is pretty much fully original. I have been meaning to take some pictures of the car anyway, so will post what I see and report back.

But if I have this right, a pressure test is first as the AC clutch won't engage if the system is empty? Thanks.

leathermang · #6 07-06-2010, 10:04 AM

UH... do not assume anything you don't have to...
that could be a disaster....
take pictures of the fittings on the AC system...
and look for tags which might indicate that it was changed to R134a or some junk put in it.. ask the former owners if you are able to also...

Yes, you should look to see if the compressor is engaging... see if the CENTER portion turns after you hear a click..
often two people are better than one.. one inside with the controls...and you looking under the hood..
There are lots of threads about checking and hooking up the compressor for a very short time to infuse the refrigerant.. but that move is only after you know which refrigerant..and whether your car system is able to engage the compressor on its own at this time... the implication being it has enough pressure to override the low pressure safety cutoff switch...

#7 07-06-2010, 10:09 AM

The fittings don't really mean anything these days. There are ZILLIONS of a/c systems out there with incorrect fittings, or no adapter fittings but have who knows what refrigerant inside.

The only way to know is with a refrigerant identifier instrument connected. Most any auto a/c shop has such an instrument and will test the system for little or no charge.

leathermang · #8 07-06-2010, 10:17 AM

Yes, I guess I am getting a little too trusting in my old age... the EPA requires those retro fittings and tags to be installed when another refrigerant it installed.... but it often does not happen..
So in addition to the reasons stated... since the pressure readings will also depend on the type refrigerant... find a way to test what refrigerant you have in the system first thing.

Matt L · #9 07-06-2010, 08:57 PM

Some AC shops have refrigerant identifiers. You need to find one. It is not going to be expensive for them to sample your refrigerant, and it will be free if you pay for an evacuation; they'll check it before doing any work to ensure that they don't contaminate their reclaimed refrigerant. You get money for uncontaminated, used refrigerant -- but if it's contaminated, it will cost you money to get rid of it.

Yak · #10 07-06-2010, 09:21 PM

Quote:

Originally Posted by Sulawesi

I know there are many A/C threads, especially this time of year, but I have had trouble finding a good starting point.

So where do I start? I have been searching the DIYs but am not really sure what I need, a test, a recharge, are there simple things to tell if the electrical and compression systems are working before testing the pressure etc?

Thanks for any links you can provide regarding initial diagnostics.

Start with some basics:

What type of controls in the 240 - ACC or manual? If you don't know, snap a pic of the controls and post it.
Does the blower work?
Do you get hot air on the heater settings and just no cold air with the A/C, or is the whole thing dead?
On the vent setting, is the air warmer like the heater is turned on; or about outside temp?
Is there a belt on the compressor?
Does the clutch (the very front part of the compressor) click down when you try to turn on the A/C or turn on defrost?
Are your fuses intact?
Do your A/C fittings have threads, like a tire valve (then probably R12); or snap-on fittings (then probably R-134a)?
Is there a sticker on the radiator support saying "Converted to R-134a"?

Plenty of info to be gained from looking around your engine compartment and describing what your symptoms are.

Sulawesi · #11 07-07-2010, 09:32 AM

Quote:

Originally Posted by Yak

Start with some basics:

What type of controls in the 240 - ACC or manual? If you don't know, snap a pic of the controls and post it.
Does the blower work?
Do you get hot air on the heater settings and just no cold air with the A/C, or is the whole thing dead?
On the vent setting, is the air warmer like the heater is turned on; or about outside temp?
Is there a belt on the compressor?
Does the clutch (the very front part of the compressor) click down when you try to turn on the A/C or turn on defrost?
Are your fuses intact?
Do your A/C fittings have threads, like a tire valve (then probably R12); or snap-on fittings (then probably R-134a)?
Is there a sticker on the radiator support saying "Converted to R-134a"?

Plenty of info to be gained from looking around your engine compartment and describing what your symptoms are.

Answers:
- It is a manual, a single dial ranging from "0" to "Max"
- The blower, meaning the fan circulating air through the interior, yes it works.
- Heat works fine.
- The center vents return outside air. If it is cold outside and the heat is on, they return cold air.
- There is a belt on the compressor.
- The clutch does not kick down. The very front of the compressor is unaffected by changes to the A/C or defrost settings.
- All fuses look fine.
- The A/C fittings have threads, there are no stickers or anything denoting R-134, the compressor says R-12 on it, though I realize that is not super informative.

Sulawesi · #12 07-07-2010, 09:57 AM

and one more detail...

Previous owner records "R-12 Freon added (may have been last time it was added)" This was at 145K miles, 37K miles ago, and in 1999 (11 years!). No A/C service since that time.

#13 07-07-2010, 10:41 AM

I'm not going to recover that refrigerant into my recovery tank based on log book entries made by someone other than the car owner.

Most any auto a/c shop has a refrigerant identifier and can tell you in five minutes if it is 12, 134 or a junk refrigerant. Don't make an assumption on this.

Sulawesi · #14 07-07-2010, 11:03 AM

Quote:

Originally Posted by LarryBible

I'm not going to recover that refrigerant into my recovery tank based on log book entries made by someone other than the car owner.

Most any auto a/c shop has a refrigerant identifier and can tell you in five minutes if it is 12, 134 or a junk refrigerant. Don't make an assumption on this.

Making no assumptions, just reporting what I know...

Yak · #15 07-07-2010, 05:49 PM

Quote:

Originally Posted by Sulawesi

Answers:
- It is a manual, a single dial ranging from "0" to "Max"
- The blower, meaning the fan circulating air through the interior, yes it works.
- Heat works fine.
- The center vents return outside air. If it is cold outside and the heat is on, they return cold air.
- There is a belt on the compressor.
- The clutch does not kick down. The very front of the compressor is unaffected by changes to the A/C or defrost settings.
- All fuses look fine.
- The A/C fittings have threads, there are no stickers or anything denoting R-134, the compressor says R-12 on it, though I realize that is not super informative.

It sounds like you have the proverbial "it justs needs charged" condition, but that probably means you have some leaks somewhere.

I'd suggest taking it to a shop, have them check for R12 or 134a or "other". If they can, have them do a vacuum test to check for system integrity. This is not conclusive, but will help. They may also be able to pressure check with nitrogen. Yes - you're paying for someone to test your system but hopefully will save your time and effort and give you a baseline for repairs.

Or, if you have a voltmeter with probes, you can test to see if the compressor is getting 12V in order to engage the clutch. If so, and the clutch isn't engaging; then you'll troubleshoot the clutch. If it's not getting 12V, then you'd work upstream.

You may be able to jumper the low-pressure switch and trick the system into engaging. That might tell you the clutch works, but not much more unless there's refrigerant in the system.

If the last record of service was 11 years ago, you will probably have some leaking O-rings, maybe some hose issues, possibly a bad compressor.