Mein AC ist kaput... - Page 2 - PeachParts Mercedes-Benz Forum

ashedd · #16 10-31-2009, 04:43 PM

Quote:

Originally Posted by snookwhaler

I remember reading somewhere recently that if you just unhook the connection from the mono-valve you will have full heat.

So very true. My TD heat works very well... unplug the valve and you will die from heat exposure.

MercFan · #17 10-31-2009, 09:58 PM

I did some testing tonight - unplugged mono valve, looked at the connector and the terminals - the terminals were a little crusty but no too bad - I cleaned it all with wire bush, connector cleaner and brake cleaner - came out shiny clean.

Next, I hooked up the voltmeter to the exposed plug that normally goes into the monovalve and with the key in the ignition (on setting II), I got the following readings (pressing the ACC keys from right to left):

Key 1 (with a CIRCLE) - full 12V
Key 2 (EC) - 0V
Key 3 (solid and empty arrow) - 0V
Key 4 (both solid arrows) - 0V
Key 5 (Defrost) - 0V

This seems very strange to me - it seems a bit backwards, but that's just me... I thought that in its normal setting with everything off the voltage at the monovalve should be 0V and with Defrost key on it should be 12V - but it seems that I've got the exact opposite...

Am I testing it right?! The previous posters mentioned that the voltage is 'switched at the ground' - I didn't know what that meant... or if there's a better way to test it.

Thanks -

#18 10-31-2009, 10:05 PM

It is a little backwards. The valve goes to the full open position without power, so it needs voltage to hold it closed. When the climate control is turned of, the 12V keeps the valve closed (no heat). Its behavior with other settings depends on the temperature setting.

Also, I believe the control is on the ground side, not the live side so I'm not sure how to best test it.

MercFan · #19 10-31-2009, 11:15 PM

Quote:

Originally Posted by Craig

It is a little backwards. The valve goes to the full open position without power, so it needs voltage to hold it closed. When the climate control is turned of, the 12V keeps the valve closed (no heat). Its behavior with other settings depends on the temperature setting.

Also, I believe the control is on the ground side, not the live side so I'm not sure how to best test it.

I should also mention the readings that I reported were with the ignition on but the motor was NOT running... not sure that makes a difference (just making sure you have all the info).

Another thing I've noticed while clicking the buttons and watching the multimeter is that when I press buttons 3, and 4 there was a little audible 'click' (like a relay click) in the ACC unit and for just a split-second I saw the voltage reaching about 9V+ before quickly plummeting down to 0V... strange...

I wonder what I should check next?! What controls the modulation of the mono-valve the KLIMA relay or something else?!

Finally, is there a good link on how to test the mechanics of the mono-valve?! I've been reluctant to pull it apart thinking that I will spill coolant out of the top - possible?! Can I just take mono-v without any fuss and test it in a stand-alone mode by hooking it up directly to 12V?!

#20 10-31-2009, 11:26 PM

I forgot you had a KLIMA in your 85 but I don't believe that affects the mono-valve, just the AC. You really need to get your hands on a wiring diagram for your specific car so you can troubleshoot. Hopefully, someone here has the diagram.

Let me ask a basic question, does the heat seem to work normally? If the heat is working (adjusting the temperature based on the setting), the mono-valve and it's controls are probably OK.

When you select AC, do you get hot air, or just outside temperature?

MercFan · #21 11-01-2009, 12:42 AM

Quote:

Originally Posted by Craig

Let me ask a basic question, does the heat seem to work normally? If the heat is working (adjusting the temperature based on the setting), the mono-valve and it's controls are probably OK. When you select AC, do you get hot air, or just outside temperature?

I just took the car for a drive - wanted to make sure nothing changed after clearning the ACC unit a couple of days ago... turns out it's still the same:

I was in an 'Auto' mode and set the dial to about 26 deg C and left it there for most of the drive. The Button #3 was pressed (floor heat I think). The fan would start running immediately blowing cool air (car was still cold). The car would gradually warm up and the heat would increase respectively. Soon the heat was really coming out - same fan speed but in no time it was hot enough to roast turkeys on those side vents and I had to take corrective action to cut the heat lest I be cooked to a crisp. Pressing the low fan speed reduced the heat out of the vents considerably to a comfortable level, but the heat NEVER cut out on its own, until I could no longer take it and had to manually turn it off (button #1 with an O on it). So this isn't looking well for the 'Auto' mode.... something is definitely wrong - it's like it's not registering that the desired temperature has been reached and it's time to shut down the blaster... It's always hot (when engine is hot) and it's either ON or OFF (manually shut off), with no in between states.

Another test:
Starting with buttons in the OFF position (with button #1 engaged) I pressed the EC button (button#2) to test that. The fan started running very gently, it would gradually increase in speed, stepping it up about 2,3 or 4 times until finally reaching blast-furnace state and requiring manual intervention again, or risking melted steering wheel...

The heat level was constant I think, only the fan would run faster and faster making it very very hot in 10-15 seconds... Pressing the OFF button (button #1) would bring much needed relief from the heat wave.

Finally you asked about outside air - the answer is no, I never get outside air to flow - assuming engine is warmed up: if it's on it's HOT and that's it.

THanks for reading - sorry, it's kind of long.
James

#22 11-01-2009, 07:23 AM

Well, it sounds like the monovalve works, and it sounds like the pushbutton unit is controlling the fan correctly. However, it sounds like the temperature control is not working to modulate the heat. I'm not sure if the next step is to repair/replace the pushbutton unit or not. Personally, I would probbaly give these guys a call and see what they recommend:

http://gdl-online.com/begin1.html

MercFan · #23 11-01-2009, 08:21 AM

Quote:

Originally Posted by Craig

Well, it sounds like the monovalve works...

Thanks Craig - I'll try calling them on Monday. You know of any W123s in the local junkyards that I could scope out?!

Also, how do you come to the conclusion that monovalve works - I'm just wondering. If the default position on the mono is heat, then either it doesn't move properly when the 12V are applied, OR the ACC unit does not deliver 12V to the mono terminals at the proper time (this is probably the case, I'm guessing)... But I'm not sure there's any proof that mono works either because I have never experienced cold air or outside air through that vent so I have no reason to believe that the mono has ever been activated.

Is there a way to isolate the monovalve to test it stand-alone just to eliminate that variable once and for all?!

Thanks,
James

#24 11-01-2009, 08:34 AM

If I understood your post, the heat shut off when you turned of the climate control so I assumed the valve was closing (or were you just saying that the fan stops?).

Have you verified the valve actually clicks closed when you shut off the heat?

If you start and run the car with the heat off, can you verify that the heater hose stays cold when the engine heats up? That would verify the valve is staying in the closed position.

I've never really gone looking for junk yards, no time.

MercFan · #25 11-01-2009, 09:14 AM

Quote:

Originally Posted by Craig

If I understood your post, the heat shut off when you turned of the climate control so I assumed the valve was closing (or were you just saying that the fan stops?). Have you verified the valve actually clicks closed when you shut off the heat?

No, the heat never turns off. I can only shut off the fan, but not the heat... I'll need to listen for the valve closing/opening next time. Can I apply 12V to the monovalve directly (with jumper wires from battery) without damaging?!

Another related question: would the ACC unit from a W126 body work in my W123?! Like this one:

http://cgi.ebay.com/ebaymotors/Mercedes-w126-420sel-560sel-Climate-Control-w123-300d_W0QQcmdZViewItemQQhashZitem1c0d9bf9f8QQitemZ120487410168QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAcc essories

#26 11-01-2009, 09:23 AM

Sorry, I misunderstood. I have put 12V on my monovalve without hurting anything, but no do it at your own risk. It's possible that you just have a leaking monovalve, have you taken it apart and looked at the rubber parts?

I believe the W126 unit is different. I would be careful with used units, you never know if they are good.

MercFan · #27 11-01-2009, 09:27 AM

Quote:

Originally Posted by Craig

...have you taken it apart and looked at the rubber parts?...

I have not taken it apart yet - but I want to... will I lose much coolant if I take it all apart there at the firewall or is it a a high point in the system?!

#28 11-01-2009, 09:39 AM

It's pretty much the high point, you'll only lose a few drops. Remove the pressure cap first just to make sure.

MercFan · #29 11-01-2009, 04:04 PM

First of all, I've applied 12V directly to the prongs on top of the monovalve and I could feel the plunger moving inside each time I energized the coil. I have then taken apart and serviced the valve. Look at the photo attached and notice that the diaphragm is torn on it. So some questions:

1) Can I just buy the diaphragm replacement or do I have to purchase an entire new monvalve (around $50)?!

2) I don't understand how a torn diaphragm might jeopardize the operation of that circuit. Seems that the rubber grommet that's at the end of the plunger if in good shape would inhibit the flow of coolant regardless of the condition of the diaphragm... what am I missing?!

3) How far should the pluger normally extend out - looks line mine only extends maybe 3-5mm - not far at all - definitely not enough to stretch it and expose the rip in the diaphragm when voltage is applied. I had to physically pull on it to see the hole. Just wondering if the travel on mine is sufficient.... Maybe my next round of tests can tell me if it's sufficient.

So should I spring for a new mono valve !??? This is perhaps part of the problem but I don't think it's the entire problem. There's more...

#30 11-01-2009, 04:12 PM

Yup, that's a common failure. You don't need a whole valve, just the "repair kit":

http://catalog.peachparts.com/ShopByVehicle.epc?q=1985-Mercedes--Benz-300d-Climate--Control&yearid=1985%40%401985&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6193%3AMBC%7C1504%3AED%7C10000135%40%40300D&catid=242213%40%40Climate+Control&subcatid=242328@@Mono+Valve+Repair+Kit&mode=PA

I don't remember the exact position of the plunger in the valve (it's been a while), but if it's torn you need to replace it.

That may not be the entire problem, but it probably has something to do with the heat not shutting off. I don't know if there's a cheaper source for the monovalve kit, I haven't bought one in a few years.