Mercedes-Benz Forum banner

1 - 20 of 27 Posts

·
One of the BW Old Guard/R129, W204 Moderator
Joined
·
7,143 Posts
Discussion Starter #1
Decided to address this with the group directly, and abandon earlier thread.

I am chasing a problem with the ACCII system on the '78 I am helping with. Vacuum good, master switch 19 working, blower functional (when "hot-wired"), all fuses good, servo good...

Everything buttoned up correctly and... NO BLOWER ON ANY SETTING!

I have the fan plug off the servo controller, and I have put 12V on one of the fan terminals (medium speed, but did not note which terminal number) to get the blower to work. What I have now is a fully-functional system, except no fan speed control. In DEF, I get HOT air thru def vents as designed, center vents (and floor vents) are closed. In Bi-Level, the pods switch over correctly, but the temp wheel seems not to respond as the servo drives to the cool side (water off)regardless of the temp wheel setting, and the air comes from the floor and then center vents (slowly switches over from floor to center as the air temp cools). Appearances are the system thinks the interior of the car is warm enough, and drives the servo to turn off the water. In auto high or low, the air comes from the center vents (of course the fan speed does not change) as designed, but is cool only.

In summary, Def is hot, all other functions drive the servo to what appears to be the park position, and only ambient cool air comes thru the selected vents. If I disconnect the fan wire and replug the fan plugs onto the servo, I can make the servo transit from hot to cool with the temp wheel, but NO FAN!

Also, the aux water pump runs "sometimes", seeming to be only when the engine is cold, but above 40C. After engine warms up, I have not seen the water pump run.

This is driving me crazy... I am gonna have to take a break from this one. At least the owner can get warm/hot air from the def as I have it hooked up now (and a little from the floor gets thru in Def setting, probably from bad seals).

Of course, the dash end vents work, but I didn't mention them in the diatribe above for obvious reasons...

This is a poorly-maintained 1978 450 that the present owner has had for a few years. He bought it with problems, and only now has he found a "sucker" willing to help him resurrect it. We have removed the seats and re-padded them. rebuilt the WUR and verified plumbing, cleaned the tank, the FD, and all lines. Had the injectors pop-tested, and verified fuel pressures. Car is running 95% satisfactory, but still needs a little tuning. Adjusted the HT lock-downs to mount correctly, overhauled the top latching system (the levers on top release and cable adjustment), adjusted the soft-top cover to close properly, fixed the loose AC controls in the dash, and various other items. Been successful so far, but ACCII has us stymied. IF servo were bad, I'd put in Unwired Tools kit, but no need in this case.
 

·
Registered
Joined
·
4,103 Posts
Everything buttoned up correctly and... NO BLOWER ON ANY SETTING! I disconnect the fan wire and replug the fan plugs onto the servo, I can make the servo transit from hot to cool with the temp wheel, but NO FAN!
With a discription like that. lol




1. Check all fuses in the fuse panel in the Right Hand (RH) kick panel, also the in-line fuses located directly above the fuse panel for the AC amplifier.

2. If all OK, then verify power inputs to the AC amplifier located behind the glove box.

3. Using a Digital Multimeter, (DMM) Pin #6 on the amplifier the Red/Yellow/Green (RD/YL/GN) wire should be battery voltage (B+) at all times. Pin #8 on the amplifier Black/Pink/White (BK/PK/WT) wire should be B+ with the key in the on position from AC/start relay. Pin #4 Brown (BN) wire should be a constant ground. Pin #2 White (WT) wire should be B+ with the key on and control panel pushbutton in the DEFROST position.

2. By backprobing the connector across terminals #1 Green/Yellow (GN/YL) and #7 Black/Violet/White (BK/VI/WT) with the DMM leads, check for voltage output while switching the temperature selector wheel between hot and cold, with Key On Engine Running (KOER). The amplifier is capable of reversing the polarity output on these wires to the servo motor so the polarity of the DMM connections is unimportant. As the temperature selector is adjusted, the voltage output on these wires should change. This indicates a correctly functioning amplifier. If there is no change in the temperature or airflow, then the servo is stuck or shorted/open circuit.

And if that doesnt work, go to this.

1. Check vacuum supply to pushbutton switch on control panel from engine key on engine running.

2. Test power feed into climate control amplifier behind glove box using a Digital Multimeter (DMM). Pin #8 Black/Pink/White wire should be Battery Positive Voltage (B+), Pin #6 Red/Yellow/Green should be B+ key on from in-line fuse. Pin #4 Brown is ground. Pin #2 White wire should have B+ when mode switch is in Defrost position.

3. Start engine and disconnect connector at amplifier. Use a fused (5A) jumper wire from B+ to connect to Green/Yellow wire at connector, and from ground to Black/Violet/White wire at the connector. This applies voltage directly to the drive motor in the servo. After a few seconds the temperature should change. If not, reverse polarity and retest. If there is no temperature change, the servo is defective.


And if none of that works. Heaven forbid.

1. With key on, select different temperature on climate control panel while listening for climate control servo motor operation. If servo motor does not run, diagnosis of servo needs to be performed.

2. With servo operating test of main blower vacuum switch is needed. Remove climate control panel and find main vacuum switch. It has a green vacuum line attached to it and it is to the far right of the four vacuum switches. Remove wiring connectors from switch and jump them together. Wire colors are Green/Yellow and Green/Yellow/Red. With key on does blower run at low speed?

3. Test for vacuum to switch with engine running. If vacuum is correct and blower runs with switch by-passed, the switch is faulty.
 

·
One of the BW Old Guard/R129, W204 Moderator
Joined
·
7,143 Posts
Discussion Starter #3
Some of this already done, so I will respond individually in context. Others sound like good checks to perform, and will be top on the list:

With a discription like that. lol
Luck, I'm gonna need...

1. Check all fuses in the fuse panel in the Right Hand (RH) kick panel, also the in-line fuses located directly above the fuse panel for the AC amplifier.
Done. All good, including 2A in separate holder, and verified by DMM, not just visual.

2. If all OK, then verify power inputs to the AC amplifier located behind the glove box.
Done

3. Using a Digital Multimeter, (DMM) Pin #6 on the amplifier the Red/Yellow/Green (RD/YL/GN) wire should be battery voltage (B+) at all times. Pin #8 on the amplifier Black/Pink/White (BK/PK/WT) wire should be B+ with the key in the on position from AC/start relay. Pin #4 Brown (BN) wire should be a constant ground. Pin #2 White (WT) wire should be B+ with the key on and control panel pushbutton in the DEFROST position.

2. By backprobing the connector across terminals #1 Green/Yellow (GN/YL) and #7 Black/Violet/White (BK/VI/WT) with the DMM leads, check for voltage output while switching the temperature selector wheel between hot and cold, with Key On Engine Running (KOER). The amplifier is capable of reversing the polarity output on these wires to the servo motor so the polarity of the DMM connections is unimportant. As the temperature selector is adjusted, the voltage output on these wires should change. This indicates a correctly functioning amplifier. If there is no change in the temperature or airflow, then the servo is stuck or shorted/open circuit.
Will check with this procedure, but be advised: With all connections restored as factory, the servo will transit from hot to cold in Bi-Level, etc with rotation of temp wheel. Verified with top off of servo and watching pot rotate, and temp of air change with rotation. Servo parks correctly in all cases. Fan just will not run. In bypass and on bi-level, fan will not turn on until vacuum switch makes, shortly after engine running. Heavy acceleration and vacuum drops, so fan shuts off briefly until vacuum restores. Indicates vacuum leak, but not bad enough to prevent function at idle or moderate acceleration.

And if that doesnt work, go to this.

1. Check vacuum supply to pushbutton switch on control panel from engine key on engine running.
vacuum present... all flaps change as per design when running on my bypass...

2. Test power feed into climate control amplifier behind glove box using a Digital Multimeter (DMM). Pin #8 Black/Pink/White wire should be Battery Positive Voltage (B+), Pin #6 Red/Yellow/Green should be B+ key on from in-line fuse. Pin #4 Brown is ground. Pin #2 White wire should have B+ when mode switch is in Defrost position./
will verify as instructed, but be advised as per above function when hooked back up per factory.

3. Start engine and disconnect connector at amplifier. Use a fused (5A) jumper wire from B+ to connect to Green/Yellow wire at connector, and from ground to Black/Violet/White wire at the connector. This applies voltage directly to the drive motor in the servo. After a few seconds the temperature should change. If not, reverse polarity and retest. If there is no temperature change, the servo is defective.
I believe I have confirmed servo is functioning properly with above information.


And if none of that works. Heaven forbid.

1. With key on, select different temperature on climate control panel while listening for climate control servo motor operation. If servo motor does not run, diagnosis of servo needs to be performed.
As indicated from info above, servo appears to function. Def is hot, and servo parks when ignition shut off, visually verified by watching pot turn. In bypass, air transits from hot to (park) cool when switched to bi-level... sounds like dead amp or loss of power to amp when switched to bi-level, etc. When hooked up per factory, recall that the servo will transit from hot to cool, past park (I marked spots on pot case as reference).

2. With servo operating test of main blower vacuum switch is needed. Remove climate control panel and find main vacuum switch. It has a green vacuum line attached to it and it is to the far right of the four vacuum switches. Remove wiring connectors from switch and jump them together. Wire colors are Green/Yellow and Green/Yellow/Red. With key on does blower run at low speed?
#19 I presume (master switch)... Verified vacuum is closing this switch from previous test, I believe.

3. Test for vacuum to switch with engine running. If vacuum is correct and blower runs with switch by-passed, the switch is faulty.
Will test #19 as per your instructions regardless, but be advised: In bypass, I can remove vacuum (unplug black vacuum line on the thermo on the bottom of the servo) and the fan will cut off, indicating #19 master switch is closing with vacuum.

Whew...!
Thanks
 

·
One of the BW Old Guard/R129, W204 Moderator
Joined
·
7,143 Posts
Discussion Starter #4 (Edited)
With a discription like that. lol
I appreciate your time in helping diagnose this. Attached, please find a schematic of my by-pass... Also note poor quality of .pdf schematic found on MB CD (printed manual clear, however).

One further note to mention:

With my bypass, if the ignition is switched off while in def, the fan continues to run obviously; however, if the system is turned off, the fan shuts off too when by-passed. I guess the controller switches ground.

Thanks again...

Rory
 

Attachments

·
Registered
Joined
·
4,103 Posts
Sorry I forgot one.





1. Check engine for any vacuum leaks. Check for vacuum supplied to port #6 of pushbutton vacuum switch on rear of control panel, green or green/yellow vacuum hose, with key on engine running (KOER). Minimum spec is 15" vac./51Kpa at idle.

2. Set mode switch in off position. Connect hand vacuum pump/tester to port #6 on pushbutton control vacuum switch, press mode switch to 'OFF' position. Block ports #1, #2, #5 and #7 on switch. There should be no leak. Pull the blockoff plugs from ports #1 and #2. Vacuum should flow through when applied to #6.

3. Push Auto-Lo or Auto-Hi button. Block ports #2 and #3 on the switch. Pump tester to apply vacuum. There should be no leak. Pull the blockoff plugs from ports #2 and #3. Vacuum should flow through from #6.

4. Push Bi-Level or DEFrost button. Plug ports #3 and #4 on switch. There should be no leak. Remove the plugs on #3 and #4. Vacuum should flow through from #6.






This part of an email sent to me from out in t.v. land:

He has replaced the compressor and put 134a in it and the compressor runs well, low side hose gets cold, but output air from ducts is very hot? Does it seem to switch modes when operating the pushbuttons and will blow from def. or bi-level vents but temp won't respond? I faxed wiring schematics. Suggest he listen at servo when switching temp key on engine off and see if there is any noise from servo as if motor is running. If not check all fuses, but since pushbutton and blower is working he either has a dead servo or a bad amplifier.Servo make no noise whatever when temp selector is switched. I suggested if he uses a fused jumper lead to pin 5 and ground pin 4 or vice-versa with the connector unplugged on servo, it should operate the servo motor and should affect in car temp. If no noise the servo is dead. If so likely amplifier may have been damaged also, replace.
He can drive the servo motor by applying power and ground and that moves it and changes the temperature, so likely has a bad amplifier not powering the servo.



Return email:

Tried the Servo first. It was bad. Then the AMP. It was bad. New parts and now it works as factory. Melted socket for the fuse. Had to replace.
 

·
Registered
Joined
·
4,103 Posts
I appreciate your time in helping diagnose this.
No problem.


Handbasket my ass, more like basket case. lol. Sorry I had too.
 

·
One of the BW Old Guard/R129, W204 Moderator
Joined
·
7,143 Posts
Discussion Starter #7
Sorry I forgot one.

1. Check engine for any vacuum leaks. Check for vacuum supplied to port #6 of pushbutton vacuum switch on rear of control panel, green or green/yellow vacuum hose, with key on engine running (KOER). Minimum spec is 15" vac./51Kpa at idle.

2. Set mode switch in off position. Connect hand vacuum pump/tester to port #6 on pushbutton control vacuum switch, press mode switch to 'OFF' position. Block ports #1, #2, #5 and #7 on switch. There should be no leak. Pull the blockoff plugs from ports #1 and #2. Vacuum should flow through when applied to #6.

3. Push Auto-Lo or Auto-Hi button. Block ports #2 and #3 on the switch. Pump tester to apply vacuum. There should be no leak. Pull the blockoff plugs from ports #2 and #3. Vacuum should flow through from #6.

4. Push Bi-Level or DEFrost button. Plug ports #3 and #4 on switch. There should be no leak. Remove the plugs on #3 and #4. Vacuum should flow through from #6.
I will check as you mention here, but I thought I already proved the vacuum was integral enough to work, ie the flaps/vent are changing with the pushbutton as designed. Does this not more-or-less prove the vacuum system is nominal? Also, as mentioned earlier in my reply, When on bypass, the fan runs until I remove vacuum, then it shuts off (in bi-level). It restarts when I return vacuum. Note the schematic I supplied.. The voltage I am supplying is routed thru the #19 master switch. If there were no vacuum, the fan would not run, except on DEF (as voltage supplied via dual-contact relay#18).

t.v.land said:
... Does it seem to switch modes when operating the pushbuttons and will blow from def. or bi-level vents but temp won't respond? I faxed wiring schematics. Suggest he listen at servo when switching temp key on engine off and see if there is any noise from servo as if motor is running. If not check all fuses, but since pushbutton and blower is working he either has a dead servo or a bad amplifier.
Once again, servo runs, makes noises, verified visually it transits from hot to cool, and parks when ignition shuts off. Air goes from hot (def) to cool (when any other setting is chosen), so water valve is opening and closing. All this should be sufficient to prove servo is functioning.

I am suspecting, at this point, that the amp is dead/intermittent. Gonna remove it and inspect for poor solder joints, I think.

Now, the 50,000 question... Should the temp control work (servo function) with the fan bypassed as I have it (reference supplied schematic earlier). From my study of the schematics, I can see no reason why not. Reiterated, on DEF, the air is HOT!... blowing from def vents. When bi-level is chosen, the air moves from DEF to the FLOOR. As the air cools (because the servo transits from hot to park), the air moves from floor to center vents, regardless if the temp wheel is set at 85F or any other setting. ambient was 50F, engine was ~70C during tests... I even cooled the interior temp sensor with a blast of canned air (turned upside-down) and the servo did not respond. Obviously the AMP is not doing its job (or something in the sensor chain).
 

·
Registered
Joined
·
4,103 Posts
I will check as you mention here, but I thought I already proved the vacuum was integral enough to work, ie the flaps/vent are changing with the pushbutton as designed. Does this not more-or-less prove the vacuum system is nominal? Also, as mentioned earlier in my reply, When on bypass, the fan runs until I remove vacuum, then it shuts off (in bi-level). It restarts when I return vacuum. Note the schematic I supplied.. The voltage I am supplying is routed thru the #19 master switch. If there were no vacuum, the fan would not run, except on DEF (as voltage supplied via dual-contact relay#18).



Once again, servo runs, makes noises, verified visually it transits from hot to cool, and parks when ignition shuts off. Air goes from hot (def) to cool (when any other setting is chosen), so water valve is opening and closing. All this should be sufficient to prove servo is functioning.

I am suspecting, at this point, that the amp is dead/intermittent. Gonna remove it and inspect for poor solder joints, I think.

Now, the 50,000 question... Should the temp control work (servo function) with the fan bypassed as I have it (reference supplied schematic earlier). From my study of the schematics, I can see no reason why not. Reiterated, on DEF, the air is HOT!... blowing from def vents. When bi-level is chosen, the air moves from DEF to the FLOOR. As the air cools (because the servo transits from hot to park), the air moves from floor to center vents, regardless if the temp wheel is set at 85F or any other setting. ambient was 50F, engine was ~70C during tests... I even cooled the interior temp sensor with a blast of canned air (turned upside-down) and the servo did not respond. Obviously the AMP is not doing its job (or something in the sensor chain).
It could be both or not either, hell this could be a short in the wiring. Thats the problem with odd problems you never know what its going to be.



When I get cars people have modified, I try to take them back to oem, even before I decide what to do next. You might have to test the parts seperate from the car to get the answer. I cant wait for the answer. I will stay right with it, I like to see projects finished too. lol.
 

·
One of the BW Old Guard/R129, W204 Moderator
Joined
·
7,143 Posts
Discussion Starter #9
When I get cars people have modified, I try to take them back to oem, even before I decide what to do next. You might have to test the parts seperate from the car to get the answer. I cant wait for the answer. I will stay right with it, I like to see projects finished too. lol.
Thankfully, the ACC does not seem to have been monkey'ed with, other than a replacement servo sometime prior to present owner (unit looks like new inside, and that it is still functioning leads me to believe it is a replacement).

Yeah, this IS a project that will occupy some of my time to come. Still, I believe the temp control should work with fan bypassed as I have. When I un-plug my bypass, restore the fan plug, and run the system (w/o fan), I can make the servo transit from hot to cold with the temp wheel. I just can't seem to understand why unplugging the fan and installing my bypass causes the temp control to be unresponsive. Present owner is satisfied with just the def working for now, so I don't know if I'll get to address it soon (I hope so, because I want to ferret this out).

I'll post any new findings for sure...
 

·
One of the BW Old Guard/R129, W204 Moderator
Joined
·
7,143 Posts
Discussion Starter #10
The owner of the vehicle I have been working on has an idea that may blossom into something... Gotta research a bit more, but, since his servo is "working", he asks, "...why not bypass the lower (water) end of the servo and install a manual water valve, al a early 107?" His idea has merit, but is not the answer, I think. I told him I just need some more time with the old gal. Perhaps after Thanksgiving...

I'm thinking a wire is broken somewhere and/or the amp is fubar, since there are more than one issue now to investigate (fan/blower control, and servo/sensor chain/amp issue).
 

·
One of the BW Old Guard/R129, W204 Moderator
Joined
·
7,143 Posts
Discussion Starter #11
I realize I have not updated this thread. Owner is satisfied right now, and life has gotten in the way of me spending any more time on it (new job/move pending, etc). I guess this chapter is closed without resolution. I am sure his amp is dead, and I think he has a wiring issue on the climate control panel... Alas, I guess I'll never see this one thru to fruition. I am hoping he finishes the project for his sake...
 

·
Registered
Joined
·
4,103 Posts
I realize I have not updated this thread. Owner is satisfied right now, and life has gotten in the way of me spending any more time on it (new job/move pending, etc). I guess this chapter is closed without resolution. I am sure his amp is dead, and I think he has a wiring issue on the climate control panel... Alas, I guess I'll never see this one thru to fruition. I am hoping he finishes the project for his sake...
I fell there is a "The End" missing also.
 

·
One of the BW Old Guard/R129, W204 Moderator
Joined
·
7,143 Posts
Discussion Starter #13
Back on task with some measure of success. I removed bypass and placed everything back to factory... Some more sleuthing/checking, etc. Results are as follows:

In all cases, engine running and warm:

DEF
works... Servo drives to hot side of quadrant, fan runs, and warm air emanates from the def vents.
AUX water pump NOT running

BI-LEVEL
Blower does not run
"Think" I heard vacuum pods opening/closing
Servo responds to temp wheel, driving toward cool side of quadrant when set at 65F, to hot side when set to 85F
AUX water pump NOT running

AUTO-HIGH
Blower does not run
"Think" I heard vacuum pods opening/closing
Servo responds to temp wheel, driving toward cool side of quadrant when set at 65F, to hot side when set to 85F
AUX water pump NOT running

AUTO-LOW
Blower does not run
"Think" I heard vacuum pods opening/closing
Servo responds to temp wheel, driving toward cool side of quadrant when set at 65F, to hot side when set to 85F
AUX water pump NOT running

Shut car off, servo parks accordingly...

bypassed vacuum switch on bottom of the servo by connecting black/yellow at the tees...
Still no blower on anything but DEF. Also, never witnessed the AUX water pump running...

Q1:
Where the hell is switch #19 (master switch)? I find the switches on the metal header behind the glovebox, but they are NOT numbered as per manual. I think #14 on the car is #19 in the manual (switch body is green, green/orange vacuum hose, wiring colors also agree with manual, gn/ge).
Q2:
Where the hell is the Water pump temperature switch (#21 in the manual)? Would like to verify aux water pump operation.

Any Ideas?
 

·
Registered
Joined
·
4,103 Posts
Picture of what you got going on?
 

·
Registered
Joined
·
4,103 Posts
What color are the wires on it?
 

Attachments

·
One of the BW Old Guard/R129, W204 Moderator
Joined
·
7,143 Posts
Discussion Starter #17
Q1:
Where the hell is switch #19 (master switch)? I find the switches on the metal header behind the glovebox, but they are NOT numbered as per manual. I think #14 on the car is #19 in the manual (switch body is green, green/orange vacuum hose, wiring colors also agree with manual, gn/ge).
Q2:
Where the hell is the Water pump temperature switch (#21 in the manual)? Would like to verify aux water pump operation.

Any Ideas?
What color are the wires on it?
...
 

·
Registered
Joined
·
4,103 Posts

·
One of the BW Old Guard/R129, W204 Moderator
Joined
·
7,143 Posts
Discussion Starter #20
...Q1:
Where the hell is switch #19 (master switch)? I find the switches on the metal header behind the glovebox, but they are NOT numbered as per manual. I think #14 on the car is #19 in the manual (switch body is green, green/orange vacuum hose, wiring colors also agree with manual, gn/ge).
Q2:
Where the hell is the Water pump temperature switch (#21 in the manual)? Would like to verify aux water pump operation.

Any Ideas?
Mystery #2 solved... Switch resides in the blower compartment, inline with a heater hose!

Think I have identified mystery #1 as well, labelled #14 in the car. Wire colors match schematic, as does color code on the vacuum tube.

Tomorrow is going to be fun!
 
1 - 20 of 27 Posts
Top