Climate Control Safe Mode - PeachParts Mercedes-Benz Forum

BHutch · #1 02-01-2014, 06:38 PM

I'm trying to track down the cause of a "defrost only" situation with my 300SD. I'm tired of cold feet!

I am curious to know what - if anything - causes a CCU to go in "safe mode" besides vacuum leaks.

Here's what I've tried so far:

-Replaced foot-space flap vacuum actuator
-tested for vacuum at the line that feeds all the switchover valves = OK
-plugged each line from the switchover valve to pod(at the switchover valve) to see if I could get the CCU to go out of safe mode (thinking maybe if there was a vacuum leak between the switchover valve and pod this would be a way to diagonse).
-Actuated the foot space flap with a Mity-Vac so that circuit works

What am I missing?

Could it be electrical? I.e., bad CCU?

A tangential question: what is the function of the "oriface" between the leg-space flap switchover valve and pod? It seems to slow the "action" of the pod.

Marshall Welch · #2 02-01-2014, 09:45 PM

Isn't that the sign of a failed monovalve ? Others will correct me if I'm wrong.

jimandsuzy · #3 02-01-2014, 09:55 PM

Probably a bad CCU . CCU puts voltage on the appropriate vac valve for diff functions. If no voltage out of the CCU the system goes to defrost mode because in Germany they want defrost if the heat system electronics or vac system fail. Do a search on CCU to see about possible resolder repairs. Used CCUs can be found also.

Zacharias · #4 02-02-2014, 01:52 AM

System working in defrost mode only has no relation to monovalve failure.

CCU (pushbutton unit) may be at fault, but these can fail in two ways, either from age/wear or also if auxiliary (electric) coolant pump fails (seizes). When this happens, it sends a jolt up to the CCU and fries the circuit board inside.

More info here: http://www.peachparts.com/shopforum/diesel-discussion/140870-aux-water-pump-takes-out-ccu.html

BHutch · #5 02-03-2014, 10:06 AM

Hmmmm. It would seem the only way know if it is the CCU is to swap out for new/rebuilt. That's a pricey part but for a daily driver in the Northeast in Winter floor heat is pretty nice. I just want to be sure I rule out everything else first.

Do the switchover valves ever fail? Is there a way to test by sending voltage (12V?) to a swicthover with vacuum applied to see if it opens?

Someone needs to figure out how hack the climate control system with an Arduino. What are the control voltages for all of the various sensors and actuators? I suppose if I quit my job and left my family I would have the time needed to dedicate to such an endeavor.

JamesDean · #6 02-04-2014, 11:18 AM

Quote:

Originally Posted by BHutch

Hmmmm. It would seem the only way know if it is the CCU is to swap out for new/rebuilt. That's a pricey part but for a daily driver in the Northeast in Winter floor heat is pretty nice. I just want to be sure I rule out everything else first.

Do the switchover valves ever fail? Is there a way to test by sending voltage (12V?) to a swicthover with vacuum applied to see if it opens?

Someone needs to figure out how hack the climate control system with an Arduino. What are the control voltages for all of the various sensors and actuators? I suppose if I quit my job and left my family I would have the time needed to dedicate to such an endeavor.

I replied in your other thread but I'll reply here as well.

Since blower speed control and vent control are handled separately its likely the problem is in the push button unit. I'd have to check the FSM though to be sure, but its a good starting point.

Swapping the climate control with an arduino would still require a good amount of work and circuit design since most of the items operate above the ardunio's ranges. Certainly by no means impossible but not a brief task.

The 300SD's climate control system consists of three parts:
1) Push Button Unit (relays/diodes/resistors/switches mainly)
2) Temperature Regulator (control cabin temp/vents mostly)
3) Blower Motor Control (control blower speeds)

http://www.peachparts.com/shopforum/tech-help/321019-inside-box-w126-automatic-climate-control-first-gen.html

http://www.peachparts.com/shopforum/2747579-post1.html

As to testing the switch over valves you could likely send them 12V and see if the open/close. I've never done it before though.

funola · #7 02-04-2014, 11:42 AM

Quote:

Originally Posted by JamesDean

.................................

http://www.peachparts.com/shopforum/2747579-post1.html
.....

Per pics in link, it has a few integrated circuits, not just caps, resistors and relays. What year/ model is that box from?

JamesDean · #8 02-04-2014, 11:54 AM

Quote:

Originally Posted by funola

Per pics in link, it has a few integrated circuits, not just caps, resistors and relays. What year/ model is that box from?

The push button unit is mostly resistors,diodes and relays but the blower and temperature units are more complex.

The first gen 126 and 82-85 123s used these style of climate control systems.

The unit from that post was going into 1985 300SD.

BHutch · #9 02-04-2014, 02:59 PM

So, I spoke with my Indy this morning and, based on my description of the symptoms, he feels like it is not the CCU and is leaning towards a vacuum issue. I'm going to visit him later this month and let him help me diagnose and I'll report back. I'm still a newby at working with the Vac system and Mity-Vac so I'm very prepared to believe that just because I wasn't able to spot the fault in the vacuum system it doesn't mean it isn't vacuum related.

funola · #10 02-05-2014, 12:59 PM

Quote:

Originally Posted by JamesDean

The push button unit is mostly resistors,diodes and relays but the blower and temperature units are more complex.

The first gen 126 and 82-85 123s used these style of climate control systems.

The unit from that post was going into 1985 300SD.

I have taken both my 83 and 85 W123 300D PBUs apart to fix burned out traces and I can assure you they only have resistors, capacitors, diodes and relays, NO integrated circuits. The 85 300SD must use a different PBU than 83, 84, 85 300Ds.

JamesDean · #11 02-05-2014, 01:09 PM

Quote:

Originally Posted by funola

I have taken both my 83 and 85 W123 300D PBUs apart to fix burned out traces and I can assure you they only have resistors, capacitors, diodes and relays, NO integrated circuits. The 85 300SD must use a different PBU than 83, 84, 85 300Ds.

I am confused. lol. I never said the PBUs contained ICs.

The blower control module and the temperature regulator unit do, but the PBUs are all simple components no ics.

The item from that thread was a blower motor controller, which has some ICs in it.

funola · #12 02-05-2014, 04:22 PM

Quote:

Originally Posted by JamesDean

I am confused. lol. I never said the PBUs contained ICs.

The blower control module and the temperature regulator unit do, but the PBUs are all simple components no ics.

The item from that thread was a blower motor controller, which has some ICs in it.

I got confused by your: "The first gen 126 and 82-85 123s used these style of climate control systems."

My 83 and 85 123's climate control system does not have IC's AFAIK. If they do, please let me know which box they are found in. I know my PBU's does not. Are there other 123 climate control boxes with IC's that I am not aware of?

JamesDean · #13 02-05-2014, 04:33 PM

Quote:

Originally Posted by funola

I got confused by your: "The first gen 126 and 82-85 123s used these style of climate control systems."

My 83 and 85 123's climate control system does not have IC's AFAIK. If they do, please let me know which box they are found in. I know my PBU's does not. Are there other 123 climate control boxes with IC's that I am not aware of?

Ah! Now I understand. And you're right the PBU doesn't but the PBU interfaces with two other control units.

The climate control system used on the 126's and 123's in the early 80's consisted of three boxes:

1) push button unit
2) blower motor control unit (on 126 located left side of passenger foot well on blower box)
3) temperature regulator unit (on 126 located right side of passenger foot well on blower box)

The last two units do have some integrated circuits in them as you can see from the pictures that I posted above.

These only apply to cars with the automatic climate control system of course.

The pbu sends out control signals to these boxes and they act accordingly.

BHutch · #14 02-20-2014, 04:24 PM

Cause of no legroom flaps was a bad changeover valve - not vacuum pod or CCU.

crazy4diesel · #15 02-20-2014, 11:13 PM

What's a change over valve, and does my car have them? 83 300TD.