Hey guys,
I have read most of the entries about AC/Heat fixes but I can't seem to find what I need. I bought a 84' 300D last summer and the AC put out cold air. I went with it until the fall and figured I needed to find some heat. With the help of the Forum I determined the mono valve had been completely remove and the wires cut. I installed a recycled one, a kit and rewired the connection. With that, I had all heat. That has been doing me well for the winter, but I hope spring will be coming soon, and I want to have both heat and AC. I get lots of heat with all buttons and the button does work to shut it off. The wheel does not function at all. I replaced the tube to the sensor thinking that might help. Not!
If I have missed a thread that need to see, please let me know. I am a novice, but I have been able to fixed a couple of issues with help from you guys. Hope you'll tell me what I need to know.

You need to find a thread which gives the basic information with regards to tests on your AC system so people on the forum can be of help. Run the tests and report the results.
This means basic things like whether your compressor will turn on, whether it will turn on if you connect across the safety pressure cutoff on the dryer, and then what the pressures are in the system. If the refrigerant has leaked out and it will not turn on due to that condition you will want to limit your running of the compressor to the very shortest amount of time you can since all the lubrication is provided by the fact that the oil is mixed in the refrigerant... and if you have a Delco compressor you have no oil sump... there are huge numbers of threads on AC stuff...
And you need to tell us what you mean when you say you 'have no ac but it works'...
to us that makes no sense.

__________________
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

[
And you need to tell us what you mean when you say you 'have no ac but it works'...
to us that makes no sense.[/QUOTE]
What that means is that prior to reinstalling the mono valve that the AC worked just fine, just like I said in the post. Obviously, the post is not clear if you are telling me to run test on all the AC functions.

:EDIT: to make the issue clear...


Hey guys,
I have read most of the entries about AC/Heat fixes but I can't seem to find what I need.
I bought a 84' 300D last summer and the AC put out cold air.
I went with it until the fall and figured I needed to find some heat.
With the help of the Forum I determined the mono valve had been completely remove and the wires cut.
I installed a recycled one, rewired the connection, and had 100% heat at all settings (overpowering the A/C).
That has been doing me well for the winter, but I hope spring will be coming soon, and I want to have both heat and AC.
I get lots of heat with all buttons and the button does work to shut it off.
The wheel does not function at all.
I replaced the tube to the sensor thinking that might help. Not!
If I have missed a thread that need to see, please let me know.
I am a novice, but I have been able to fixed a couple of issues with help from you guys.
Hope you'll tell me what I need to know.

Maybe this will help:
When you try the different functions, does the air divert to the different vents for the different modes? Does everthing seem to function correctly except the temp wheel?

The reason for asking is to find out if the pushbutton controller seems to be functioning correctly. What usually happens on the controller is broken solder joints internally. If you are familiar with soldering circuitry, the repair usually involves opening the controller and looking for cracked solder joints where the boards meet in an "H" pattern. If not: http://www.programainc.com/index.php

To check if the monovalve is closing as it should, place a meter (ohms) on the "ground" side of the connector and see if it varies at all while placing the pushbutton controller in different modes and varying the temp wheel. The pushbutton controller is part of controlling the ground side of the monovalve.

But before you take a lot of things apart, double check the fuses. If the W123 and W126 are similar for that year, a fuse basically powers the monovalve and the pushbutton controller and temp controller controls the ground side of the valve. The monovalve basically goes to full hot with no power.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

PeachPartsWiki : W123ClimateControl

Climate Control Repair
on the 1983 300D Turbo (W123 Chassis)
by BoostnBenz
2/16/04
http://www.peachparts.com/Wikka/W123ClimateControl

Thanks for the help. I will check these things out.

I'm betting the PO removed the monovalve assembly for a reason - probably to get the AC to work. No telling what was wrong that he didn't fix. You may be looking at a damaged CCU. Since you reinstalled the monovalve, you understand the plumbing. A couble of quick fixes to get cold air while you trace down and fix all the factory issues:
1. You might add a manual valve to shut off hot water for the summer. or
2. Wire swtched 12V directly to the monovalve. 12V applied should cut off the heat.
Keep us posted as this is a common area of concern.

__________________
Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html

I am presently resoldering the CCU so I will see if that is a fix. I don't see any real obviously cracked connections, but I will re-melt them and add some solder where needed. I hope to get finished with it tomorrow. I will let you know if it helps. Thanks for the quick fix ideas.