Compressor workes but AC hot, 1985 300d

[calidiesel617]

This will be very challenging. So here is the current problem. If I turn on the ac the compressor engages and the referegent hose gets cold and air blows out the vents, but the air is like 130F. When I bought the car this winter It had almost no heat. Replacing the mono valve and aux water pump fixed that problem. Now I have no AC. Air blows out the vents, but the air is like 130F I have done the following to try to fix the problem.

Changed mono valve 3 times with ones from junk yard
Changed inside control panel once with junk yard one.
checked ac charge

before I changed the first mono valve (the first time) this winter to fix the heating problem I used the probes on my OME meter to see if the mono valve was getting energy, my testing was inconclusive. I then read in the service manual (not a real MB one) that connecting anything to those 2 terminals on top of the mono valve can cause "damage to the electronics"


Obviously the heater core is still getting hot water from the mono valve. What other tings can I try to fix this. aside from what I have already done. also is there anything in between the controls on the dash and the mono valve that I could have broken with my misguided OME meter probing.

Thanx so much

1985 300d turbo

[calidiesel617]

Originally Posted by ah-kay

Can you try this if you have a Digital Voltmeter? If the A/C works and the pipe is cold to touch then it is probably the monovalve.

1) Check the fuse for the monovalve. I do not remember which fuse number off hand.

2) Unplug the connector from the monovalve. Turn on A/C and probe the connector for voltage. It should have 12V. The CCU should turn off hotwater flow by putting out 12V to monovalve.

3) Turn on heat and measure the voltage again at the connector. See whether you get 0V?

4) You can try testing the monovalve by removing it from the body. Apply 12V and see whether the plunger is activated. It could be the plunger is not seating probably on the valve body to close off the flow.

5) If you do not see 12V in step (2) then you can hard-wired a 12V to the monovalve pins to override the CCU. This is to make sure the valve is closed but you should be able to resolve it prior to this step.

Good luck.

Ah, so its just an electromagnet and 12 vdc is what I am looking for with the ac on. thanx so much for your help, I will report back when I figure it out.
Thanx so much for your help .

[tangofox007]

Originally Posted by calidiesel617

Ah, so its just an electromagnet and 12 vdc is what I am looking for with the ac on.

The monovalve should have system voltage any time the key is on. Whether the a/c is on or not is not a factor.

Originally Posted by calidiesel617

Obviously the heater core is still getting hot water from the mono valve. What other tings can I try to fix this. aside from what I have already done.

You could plug or clamp a heater hose until November. That will solve the immediate problem.

Originally Posted by calidiesel617

...with my misguided OME meter probing.

I suppose that an Ohm by another name is still an Ohm!!!

[Brian Carlton]

The factually incorrect post has been deleted.

Please advise me via PM of any further posts of factually incorrect information by this member.

B.C.

Just for the record, I DO NOT contact the moderator via PM when I have a problem with someone elses post. The person whose post was removed here, private messaged me implying that I had done just that. I do it in a thread for all to see. I wish that everyone operated this way, particularly leather people from Central Texas. Making complaints to the moderator about another member in a private message behind the other members back seems quite chicken$#!+ to me.

[tangofox007]

Originally Posted by calidiesel617

Ah, so its just an electromagnet and 12 vdc is what I am looking for with the ac on.

If 12 vdc is only present when the a/c is on, what keeps the monovalve closed when the a/c is off? If 12 vdc is not present with the a/c off, you will have only two climate control options: a/c or full heat.

[vstech]

I agree. OHM is the fundamental rule for electricity.
calling a meter an ome meter can be forgiven or calling it a vom or whatever you want to call it is fine with me, but ya best not be telling the experts you are right because you know engineering and your ome is the best!

as to vocabulary and intelligence, lets not get too excited about that. this is an internationally visited website and many non english speaking members are here. (unfortunately, many of the grammatically hosed sentences are local...)
I've always understood that the most intelligent speaker is one who is comfortable and understood by all levels of intelligence. I strive to assist the morons equally with the mensa's, without offending either one.

vs makes a good point, however, OHM is a proper name. I can't imagine that it would be spelled differently in any Language.