I recently removed my AC electronic control unit, took it all apart, cleaned and replaced the missing bulbs. Also glued the dial whose plastic strip (blue and red) was all coming apart... it looks nice now, the fan blows hi/low/auto. I was hoping to spot some type of electronic circuit board problem in there - but it was all good, so I reinstalled it, but the A/C still doesn't work. All I ever get is hot air no matter what buttons I press or where I set the temp dial.

I know there've been a lot of posts on the subject, so no need to reinvent the wheel in this thread - I just need a little direciton on which troubleshooting path to pursue. Should I follow Dieselgiant's DYI to flush the lines, and refill the freon - I have a friend who can do it.

The compressor is new - the belts are new but I'm not even sure I know how to turn the compressor on... .would like to test that first. Is it possible ot measure voltage at that plug?! What should the controls be set to for that? Any suggestions, links to follow?!

THanks,
James

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Does the AC compressor run when you place the climate control unit in the defrost mode? The front of it should be engaged and spinning with the belt.

do you also get hot air through the center vents?

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As far as I can tell you are a LONG way from the point where you would be making decisions about installing the freon...

If you have done the basic tests which have been mentioned hundreds of times in threads please outline exactly what you did and the results of those tests..

Then we may can help you narrow down the problem.

At this point it almost sounds like you want to skip over the hard (and necessary )physics tests and jump to ' the easy way'.... which we would all love to do... but that is not possible... thus the huge discussions in the past on this subject...

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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/showthread.php?t=156207&highlight=evaporator

A/C thread

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

Have you checked the mono valve? Have you put gauges on the system?

No, haven't done any of it yet - I'm just wondering how to tackle it - and which of many threads to follow... guess I'll need to read up on it first and go from there. Meanwhile, if anyone has suggestions on a short list of threads that contain the test steps mentioned in previous posts it would be helpful.

Thanks,
James

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Yes I do, though the air stream seems obstructed... barely flowing out of these even with high fan speed.

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Just click on the Resources tab up top. DIY LINKS/CLIMATE CONTROL.

__________________
1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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(='.'=) This is Bunny. Copy and paste bunny into your
(")_(") signature to help him gain world domination

Ok - I followed the following links and learned some of the basics - followed the diagram tracing my components under the hood - I'm really at the very bottom here in terms of knowledge about AC, but it's quite interesting so far...

I already completed this how-to:
http://www.peachparts.com/Wikka/W123ClimateControl
Everything seemed in order there in my ACC controls - no real problems spotted anywhere.

I've read some of the Blower Motor links - like this one:
http://www.peachparts.com/shopforum/showthread.php?p=1089886
I have to take another look in my Fuse Box - I remember seeing a melted terminal in there - the fuse was missing... I'll take a photo. Is the blower motor what runs when I hit the Hi/Auto/Low fan speed buttons on the ACC control?! ... because that fan runs just fine...

Still looking for other major testing steps to follow.... RIght now I'll be investigating the melted fuse possibility and next, I'll tackle the KLIMA relay - trying to learn how to test/validate that it's closing/opening properly. It has something to do with the 'kick-down' switch which is another 'mystery' to me... should be intersting learning experience...

So this is the link I'll be studying next, I guess: http://www.peachparts.com/shopforum/showthread.php?p=1344819

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Since I'm starting 'fresh' not knowing much about the AC including the controls I thought I would start by reading the FSM manual (AC User Guide) to learn about the various buttons on the ACC unit... to my dismay the FSM guide photos of the ACC unit didn't look anything like mine - the controls pictured were all manual, the layout was all different and the button labels didn't match at all.... so someone please help me out: what do the differnt buttons supposed ot do and most importantly how do they affect the AC compressor?!

What I really need to learn is which button/dial positions should engage the AC compressor so I can do some troubleshooting to try to narrow down what may be the culprit(s).

THanks -
James

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

The short answer is that the AC should be engaged for all modes except off (circle) and economy (EC). In defrost mode you get full heat and AC, the other modes use the heat to control temperature and run the AC to reduce humidity.

First thougbt with nothing but hot air,....easy and no compressed gasses involved



If you have the newer style ACC, anything left of EC (button 2 from the right) engages compressor.


good luck

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Thanks Craig - that's what I was looking for.

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Thanks - yes, Mono valve is where i'll start my troubleshooting later this afternoon. thanks all --

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

That is where I would start. While you are checking that, you can also check the Aux. pump as it is on the same side of the car. I remember reading somewhere recently that if you just unhook the connection from the mono-valve you will have full heat.

The above post is a little misleading as pushing the EC button in conjunction with other buttons turns the compressor off. IE: Pushing just one of the ACC buttons except the "O" or the "EC" turns the compressor ON. Pushing any of the buttons (except "O") in conjunction with the "EC" button turns the compressor OFF. I did not know this until just a few weeks ago. This is nice because you are able to run the fan and control where the air goes without the A/C compressor running.

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AJ

1985 300D (SOLD)