[rwvw415]

My two center air vents have stopped blowing. They do not blow hot or cold air. Any suggestions on repairing them?

 

[RobsCountach]

My two center air vents have stopped blowing. They do not blow hot or cold air. Any suggestions on repairing them?

Ensure the center 'dial' underneath the vent is turned open. The center dial runs the center vent.

Ensure you're in AUTO mode. If not, I'd ensure the two buttons between the vents are not lite (they only function in Non-Auto mode).

Is there any fan running at all when you crank up the fan speed ? If not, I'd check the fuse first. Fan and then the A/C units.

 

[bobterry99]

My two center air vents have stopped blowing. They do not blow hot or cold air. Any suggestions on repairing them?

First diagnose the cause of the problem. Follow the attached procedure to put your climate control unit in a diagnostic mode and monitor control inputs and outputs. This is for cars 1997 and later. Refer to the table below (typed by gsm-decode in a thread a few months ago). In particular you are interested in items 63 and 64.

Nr. Description Unit

01 In-car temperature sensor °C
02 Outside temperature sensor °C
03 Left heat exchanger temp. sensor °C
05 Evaporator temperature sensor °C
06 Coolant temperature sensor °C
07 Refrigerant pressure bar
08 Refrigerant temperature sensor °C
09 Not assigned --
10 Blower control voltage Volt
20 Auxiliary fan control current mA
21 Engine Speed x100 RPM
22 Vehicle Speed km/h
23 Circuit 58d (% of batt. Voltage) %
24 Battery Voltage Volt
40 Software staus
41 Software staus
42 Variant Code 1st numerical value
43 Variant Code 2nd numerical value
50 Not assigned
51 Not assigned
52 Not assignd
60 Roof OPE/CLO
61 Left side air outlet, knurled wheel
potentiometer Volts
62 Vacuum actuator 46, feedback
potentiometer Volts
63 Center outlet, knurled wheel
potentiometer Volts
64 Vacuum actuator 47, feedback
potentiometer Volts
65 Right side air outlet, knurled wheel
potentiometer Volts
66 Vacuum actuator 48, feedback
potentiometer Volts

Item 63 is the input signal from the thumbwheel control for the center vent, and 64 is the feedback signal to the controller giving it the position of the vent flap. As you move the thumbwheel these values should continously vary from a minimum of roughly .7 to 4.5.

 

[scottc99]

Hi, great info, supposed you get an ok reading on the 63 test but the 64 test (64 Vacuum actuator 47, feedback
potentiometer Volts) is static? Does that indicate a bad Vacuum actuator? Thanks, Scott

 

[bobterry99]

It could be a bad vacuum actuator. It could also be a leaking vacuum hose or a defect in the Y11 valve block that controls the actuator. The vacuum lines are #12 and #13 on Y11, and it is located behind the passenger airbag (LHD car).

 

[lynns]

MY 2000 SL500 climate control baseline readings

This is for cars 1997 and later.

FWIW, I decided to take some baseline readings by following the above Climate Control, etc. procedure for data collection. Here are the values I received after reading MERCEDES-BENZ: A/C Diagnostics.

Sensor# - Description - Unit Value

01 Inside temperature °F = 74
02 Outside temperature °F = 79
03 Heater core exchanger temp. °F = 58
05 Evaporator temperature °F = 47
06 Engine coolant temperature °F = 192
07 Refrigerant pressure Bar = 14
08 Refrigerant temperature °F = 127
09 Not used
10 Blower control voltage = 12.5
20 Auxiliary fan control current mA = 000
21 Engine Speed x10 RPM = 060
22 Vehicle Speed MPH = 000
23 Circuit 58d (% of batt. Voltage) % = 000
24 Battery Voltage = 13.9
40 A/C Controller Software Version = 03
41 A/C Controller Hardware Version = 03
42 Variant Code 1 = 11
43 Variant Code 2 = 6-C
50 Not used
51 Not used
52 Not used
60 Roof OPE/CLO = open
61 Left side air outlet(open), knurled wheel potentiometer Volts = 4.0
62 Vacuum actuator 46, feedback potentiometer Volts = 3.5
63 Center outlet(open), knurled wheel potentiometer Volts = 4.1
64 Vacuum actuator 47, feedback potentiometer Volts = 3.5
65 Right side air outlet(closed), knurled wheel potentiometer Volts = 0.8
66 Vacuum actuator 48, feedback potentiometer Volts = 0.9

 

[grege]

Center vent problems

Hi, I have just fixed an identical problem on my 92 R129.
In my case it turned out to be a popped out connection on the distribution block under the bonnet. This had disabled the center vents, and the side vents worked, as they default to on, but were not swithing off.
Heaps easier to get at than Y11 too!
The distribution of vacuum starts under the hood in the computer modules box. Vacuum from the manifold goes into a 7 way distribution block, via some isolation valves to the transmission and others. The Red-gray one is the feed to the vacuum reservoir for the A/con. My line was a little tight and had pulled out, possibly when some work had been done on the car a while back.
Hope this helps. The diagrams in the R129 Classic DVD are very useful...
GregE.

 

[rwvw415]

Fixed the problem. It was a vacuum hose leak .Thanks Ray

 

[robinp]

Hi, I have just fixed an identical problem on my 92 R129.
In my case it turned out to be a popped out connection on the distribution block under the bonnet. This had disabled the center vents, and the side vents worked, as they default to on, but were not swithing off.
Heaps easier to get at than Y11 too!
The distribution of vacuum starts under the hood in the computer modules box. Vacuum from the manifold goes into a 7 way distribution block, via some isolation valves to the transmission and others. The Red-gray one is the feed to the vacuum reservoir for the A/con. My line was a little tight and had pulled out, possibly when some work had been done on the car a while back.
Hope this helps. The diagrams in the R129 Classic DVD are very useful...
GregE.

BRO,
SORRY TO TROUBLE U . I'VE GOT THE SAME PROBLEM , CAN U PUT SOME PICS AS TO WHERE N HOW U SOLVE THE PROBLEM . WILL REALLY APPRECIATE.
THANKS

 

[grege]

Vacuum fixes for vents / photos

Sorry Robin, thought I'd taken some photos, but cant see any, I'll pop the cover off and take a couple over the weekend..
Greg

 

[drcom]

Hi, I have just fixed an identical problem on my 92 R129.
In my case it turned out to be a popped out connection on the distribution block under the bonnet. This had disabled the center vents, and the side vents worked, as they default to on, but were not swithing off.
Heaps easier to get at than Y11 too!
The distribution of vacuum starts under the hood in the computer modules box. Vacuum from the manifold goes into a 7 way distribution block, via some isolation valves to the transmission and others. The Red-gray one is the feed to the vacuum reservoir for the A/con. My line was a little tight and had pulled out, possibly when some work had been done on the car a while back.
Hope this helps. The diagrams in the R129 Classic DVD are very useful...
GregE.

Is this just a vacuum hose under the hood somewhere?
Is it under the large plastic cover?
Where can I get a DVD?

 

[D.SHORTS]

My two center air vents have stopped blowing. They do not blow hot or cold air. Any suggestions on repairing them?

I am having a problem with my climate control on my 95 SL320. First my fan does not change speeds when the bottoms are pushed. When the bottoms are pushed only hear a slight buzz that change it pitch. To top that now when I turn on the air, I get hot air coming through the left and right air outlets, and cool air through the center outlets. Vents are open, when closed the heat moves to the center vent. Checked fuses in two locations under the hood and all fuses look OK. Tried to diagnose the system but it did not work (I done it before). Any help or suggestions?

 

[grege]

Aircond vacumm distribution

Finally got to post some pics- here they are:

See the diagnostic connector just outside the plastic covered area exposed here to show the vacuum distributor. In my case the green one was a bit tight, just pulled out of its push fit socket..

Way easier to get at than the other bits inside the car, worth a look first.

Cheers Greg

 

[bobterry99]

Tried to diagnose the system but it did not work (I done it before).

If the climate control unit can not perform diagnostics, then it seems logical to me that it can't perform some of its basic control functions as well. I would look for a used replacement module.

 

[D.SHORTS]

Thanks, was hoping it was something simple. Seem that once I tranfer Benz from California to Jacksonville, Florida I start having problems like the air and the SRS light staying on. I need to find me a mechanic other than the MB dealer.

 

[lynns]

FWIW, I decided to take some baseline readings by following the above Climate Control, etc. procedure for data collection. Here are the values I received on 8/5/07.

Sensor# - Description - Unit Value

01 Inside temperature °F = 74
02 Outside temperature °F = 79 (sitting still, engine running)
03 Heater core exchanger temp. °F = 58
05 Evaporator temperature °F = 47
06 Engine coolant temperature °F = 192
07 Refrigerant pressure Bar = 14
08 Refrigerant temperature °F = 127
10 Blower control voltage = 12.5
20 Auxiliary fan control current mA = 00
21 Engine Speed x10 RPM = 0600
22 Vehicle Speed MPH = 000
23 Circuit 58d (% of batt. Voltage) % = 000
24 Battery Voltage = 13.9
40 A/C Controller Software Version = 03
41 A/C Controller Hardware Version = 03
42 Variant Code 1 = 11
43 Variant Code 2 = 6-C
60 Roof OPE/CLO = open
61 Left side air outlet(open), knurled wheel potentiometer Volts = 4.0
62 Vacuum actuator 46, feedback potentiometer Volts = 3.5
63 Center outlet(open), knurled wheel potentiometer Volts = 4.1
64 Vacuum actuator 47, feedback potentiometer Volts = 3.5
65 Right side air outlet(closed), knurled wheel potentiometer Volts = 0.8
66 Vacuum actuator 48, feedback potentiometer Volts = 0.9

I decided to take some more readings by following the same Climate Control procedure for data collection. Here are the values I received today, 2/10/10.

Sensor# - Description - Unit Value

01 Inside temperature °F = 75
02 Outside temperature °F = 72 (sitting still, engine running)
Note: the outside thermometer read 59 (sitting still) and the climate Control dropped from 72 to 59 after taking a short drive.
03 Heater core exchanger temp. °F = 74
05 Evaporator temperature °F = 39
06 Engine coolant temperature °F = 195
07 Refrigerant pressure Bar = 13
08 Refrigerant temperature °F = 109
10 Blower control voltage = 8.0
20 Auxiliary fan control current mA = 00
21 Engine Speed x10 RPM = 0600
22 Vehicle Speed MPH = 000
23 Circuit 58d (% of batt. Voltage) % = 000
24 Battery Voltage = 13.9
40 A/C Controller Software Version = 03
41 A/C Controller Hardware Version = 03
42 Variant Code 1 = 11
43 Variant Code 2 = 6-C
60 Roof OPE/CLO = closed
61 Left side air outlet(open), knurled wheel potentiometer Volts = 4.0
62 Vacuum actuator 46, feedback potentiometer Volts = 3.8
63 Center outlet(open), knurled wheel potentiometer Volts = 4.1
64 Vacuum actuator 47, feedback potentiometer Volts = 3.8
65 Right side air outlet(opened), knurled wheel potentiometer Volts = 4.0
66 Vacuum actuator 48, feedback potentiometer Volts = 3.8

 

[mahunt]

I didn't have a problem with my A/C controls, but I was intrigued by the data that this diagnostic would provide, so I tried the procedure and accessed the information.

Unfortunately, my blower motor remains running even after I turn off the engine and remove the key. It's as if the REST button is stuck or remains on for some reason.

So that my battery wouldn't drain or my blower burn up while parked, I removed the big 30 amp blower fuse under the hood by the master cylinder/brake booster (American driver's side).

Any idea on how to correct this?

 

[speedmaster2]

heater vents

I am also having a problem with my footwell vents opening,only the upper vents would blow heat!What is the diagnostic check on my 1999 sl500?Thanks speedmaster 2.

 

[aam]

I would start looking for a shorted wire, bad relay, or ignition switch.

Regards.
aam.

 

[lynns]

I am also having a problem with my footwell vents opening,only the upper vents would blow heat!What is the diagnostic check on my 1999 sl500?Thanks speedmaster 2.

Read the bottom of the above post #3.