82' 300TD - AC has not been functional for a couple years, and with summer lurking, I'm in the 'restore it' mode.

So I had a local AC/refridge repair guy dye the system yesterday, and he found the pump shaft seal to be bad. So he replaced the pump this morning, and recharged the system.

Bugger was: the clutch wouldn't engage... tested the voltage to the clutch, and it varied: sometimes 10v, sometimes more, but apparently inadequate amperage. A few tries had the clutch "trying" to engage, but not getting the job done (can you say clutch burn-out?) We double-checked the clutch with a set of jumpers direct from the battery - the clutch worked fine, and he charged the system using this method.

**I also noted the fuse currently installed is the next heavier than listed as correct (this by a previous owner), and the box at the upper end of the fuse has whitish 'flash' marks on it, where in the past the fuse has blown...

ALSO: I could not get ANY cold air out of the ducts in the cabin, even though the refrigerant part of the system works fine, (with the jumpers), [and the aux fan cycles]. This, we're pretty sure, is caused by a vacuum module not functioning (immediate cause unknown).

Do both or either of these issues point to the CCU? Possibly needing a re-solder? I know the CCU is tired, for starters as the center (floor?) button, and the 'economy' button do not trigger the fan, but the defrost and the 'up/down' button next to it run the fan fine...

Thoughts?

That would be due to a relay problem in the CCU. Cleaning the relay contacts might help.

The compressor problem could be a relay, too. You could try swapping the compressor and aux fan relays. Also jump the low pressure switch at the receiver/drier; it could be making poor contact.

I've been doing lots of reading up - running searches on the forum...

Ran across a note about polarity of the clutch leads - does it really make any difference? Could the plug be installed upside-down, and cause an issue? Which colored wire should be 'up'?

..I'll try switching around the 'ice cube' relays also..

...and the issue with some 'door' not changing to allow the cold air into the cabin: since there's no vacuum hoses to the CCU, I'm assuming the actuators in the dash are electrically controlled vacuum pots?

The ACC controls the vacuum actuators via electrical solenoids.


There is no such door, per se. There is a recirculation flap which might not be properly positioned, but even that should allow some cooling to take place.

Interesting: the pressures are correct in the system, the condenser gets hot, etc, but NO cold air through the ducts.

I should mention, the 'temperature' control on the CCU seems to work fine, when it comes to controlling the heat side of the world... leading me to believe the mono valve is working like it's supposed to.

Just to confirm, you have normal air flow, but it isn't chilled?

All automatic temperature control is via the heater.

Correct. I just ran through the options on the CCU: fan buttons all function as indicated, defrost puts hot air to windshield. Hi-low puts air to sides and floor with temp rotated toward heat, then opens up center dash nozzles when rotated toward cool.

The fan does not run at all in floor-only, or in Economy position.
(that would be one issue)

Heat increases like it should when the temp wheel is rolled to red, moderates in white, but stays moderated (above ambient temp?) when rolled to blue. The fan does as one would expect, stepping down in the white, and stepping up as I move either direction. BUT, there is no 'cold' air.
(That would be issue number 2).

As I'm starting to understand the system: the air always passes through the evaporator - so, it's getting reheated back toward or past ambient?

Mono-valve not closing all the way?

If that translates to the center button and the EC button, the problem is almost certainly a relay in the CCU. The Bilevel and Defrost buttons power the fan thru a different relay, also in the CCU.

That's a possibility, although the fact that the heat seems to regulate normally indicates that the monovalve is not totally failed to the open position.

Even with the monovalve open, you would cold air briefly with a cold engine.

Does the a/c suction line get cold?

OK, the pollen from the grass field next door finally quit blowing for the day, and I was able to get out and play with this some more.

History: System charged 2 years ago - worked well for a few days - non-functional by the time a week had passed.

This week:
Monday: recharged system, shot in dye, found evidence of dye at pump shaft seal - ordered reman pump.

Tuesday: Installed pump. (work being done by 'old school' repair tech, who worked absolute magic at my wife's store on her sandwich bar, and heat pump - after 'local' repair outfit failed multiple times - ie: I'm tending to trust his knowledge, and he works very reasonably)

He said he saw no reason to replace the dryer, so against by better judgment, he charged the system, included one syringe of dye, and watched the gauges - pressures correct to his knowledge, but no cold air... After a very long day (he likes to talk, instead of work:/), I'd had enough, and knew it was time to go home, and hang out here to learn about the inner workings of the system as a whole.

Thursday evening: Started car, switched in AC, pump started, ran a few minutes, then kicked out. Then "tried" unsuccessfully to re-engage...

Brainchild - there's an 81 300SD in the front yard - yup, 5, read that, FIVE relays - spares. So I rotated the spare relays through both the clutch and fan positions... no change.

Jumpered around the low-pressure cut-off switch on the dryer, and wha-la, the clutch snaps in and out with attitude

but... The best the system could muster in 15 min of running is the top tube on the condenser got just hot enough to make it hard to hold my finger against... ppppfffff

So I'm guessing I'm back at square one: a leaking system.

I just talked to the tech - we'll get back together tomorrow for a more thorough and more powerful black light inspection...

Well maybe you can train him about moving AC systems.... he saw no reason to replace the dryer because he is trained on hermetically sealed systems.... sorry to hear you got caught in that squeeze....
At least running decisions by the forum provides different views...and references if necessary....
I am sorry there is dye in the system....
Are you thinking about doing the start to finish route... flush everything and go back up like we suggest in terms of leak finding ( pressure nitrogen, r22 four oz, sniffer ) ?

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

I'm thinking I want it done right, and yes, I trust the knowledge base here on the forum. If you guys weren't here, and willing to share about these old cars, I wouldn't have the pleasure of getting to drive one

(side note) I live in NW Oregon, where the weather is (tongue in cheek) 50 degrees and partly to mostly rainy 10 months of the year - being a fair-skinned redhead with low blood pressure, it's the other 2 months that'll damn near kill me without AC... If I were in Arizona, or somewhere else hot, where most everyone has working AC, the local community would likely support techs who know their moving AC systems. Here, I find the 'general repair shop' who just happens to have a few old cans of R12, and some equipment - but, regrettably, not much knowledge, and no guarantee :/

2 years ago, the only "shop" I could find in the county willing to work on the system at all, did the 'no dye sniffer' route, charged me plenty, then shrugged their shoulders and said 'sorry it didn't work out' when the system failed in less than a week. Left me still hot (under the collar too), and with a bad taste in my mouth.

Enter the current willing to work on it party. Yes, his history is with huge commercial refrigeration...

So here I am with my hat in my hand.

The point I'm at today, with a system with dye in it already - a good position to go ahead and use the big light to find the leak???
(which the 2-years-ago party couldn't find with sniffer?)

And as far as continuing forward from there...?

Here is the problem..... ( aside from having dye in there in the first place )
If your leak is in the evaporator... how are you going to see it ?
If your leak is at a high spot and on the top of the lines ... you are likely to not get enough dye out to see it...
If your leak is in a another inaccessible spot... lets say around some of our Txvalves... in the dark too...and no line of sight to all around the fitting... then you are not going to find it..

HOWEVER, if you clean out (flush) the system and pressurize it with four oz of R22 and nitrogen... the chances of finding it with a sniffer are great.. even the evaporator leaking sets off the xmass tree light signal...

I want you to know I have a lot of empathy for the fact that this is a lot of trouble for a two month span each year... here.... it is the opposite.... ten months we need AC....

We do not know the specifics of the failed sniffer test so long ago... lots of things could have caused a faulty test result.....which would not apply to a new test following our advice...

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Agreed. Compared to the cost of hiring someone to fix your problem, a heated pentode leak detector isn't all that expensive. And it will have residual value after the job is done.

I bought a used one off Ebay...for $35 plus shipping... it had battery leakage which I think I fixed... but I have never been able to check it because I have no leaks.. ( not complaining just the facts ma'am ) ...
If I knew it worked I would mail it to him...

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Just a quick touch on a Schraeder valve should tell you what you need to know.