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  #1  
Old 12-28-2016, 09:42 PM
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R129 Automatic Climate Control Question

1997 SL 600 (U.S. spec, 129.076)... climate control no longer responding to some commands... request for A/C results in compressor clutch engaging, blower speed is adjustable, as is temperature... but air no longer comes from the center or side dash vents as the vent flaps do not open.

The push button control unit (PBCU) is properly version coded and no fault codes are stored. With use of a M-B HHT in activation mode, vent flap functionality returns.

A fault code check of the instrument cluster reveals one stored fault: B1755, K2 communication, IC to PBCU (N22).

Continuity check of the K1 and K2 CAN lines between the PBCU (N22) and the instrument cluster reveals the lines are intact.

Is it safe to assume that the PBCU is faulty and warrants replacement since the heater box air flap elements are functional when the HHT is connected in activation mode?

Thanks.


Last edited by jgl1; 12-29-2016 at 03:19 PM.
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  #2  
Old 12-29-2016, 10:22 PM
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My 97 SL320 has the same B1755 code but it does not seem to affect operation.

The climate control unit ( PBCU ) is the same as a similar year C230 / C 280, you just need to change the version coding using the HHT or through the climate unit it's self.

I'd probably find another control unit and swap it out.
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  #3  
Old 12-29-2016, 11:42 PM
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Join Date: May 2012
Location: El Dorado Hills, CA, USA
Posts: 418
Quote:
Originally Posted by jgl1 View Post
1997 SL 600 (U.S. spec, 129.076)... climate control no longer responding to some commands... request for A/C results in compressor clutch engaging, blower speed is adjustable, as is temperature... but air no longer comes from the center or side dash vents as the vent flaps do not open.

The push button control unit (PBCU) is properly version coded and no fault codes are stored. With use of a M-B HHT in activation mode, vent flap functionality returns.

A fault code check of the instrument cluster reveals one stored fault: B1755, K2 communication, IC to PBCU (N22).

Continuity check of the K1 and K2 CAN lines between the PBCU (N22) and the instrument cluster reveals the lines are intact.

Is it safe to assume that the PBCU is faulty and warrants replacement since the heater box air flap elements are functional when the HHT is connected in activation mode?

Thanks.
Jg........................

90% of vent problems on these R129's-especially when no center vents are not working. The vacuum distribution block has a leak. The block has this metal 1/8"-3/16" bearing as a plug when it is manufactured(it is visable). The bearing is near the screw hole where it attaches to the inside of the engine area-Well..... The heat from the engine. Heatsinks on the bolt which causes the vacuum distribution to split open right from the bearing. Check this out on post 29:

Just bought a 93 SL500 - Mercedes-Benz Forum

Try that before a replacement climate control..

All the best,

Martin
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  #4  
Old 01-09-2017, 02:41 AM
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I can't rationalize the vacuum leak hypothesis... the vents fail to work with the PBCU, regardless of the engine compartment temperature but perform flawlessly when using the HHT in the activation mode.

Again the only fault code noted so far is for the instrument cluster reporting that it is not receiving a signal on the K2 line. Inspecting both the K1 and K2 lines revealed intact wires with no faults.

The PBCU has been sent to Beckmann Technologies for inspection and possible exchange for an overhauled unit.
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  #5  
Old 03-21-2017, 01:32 PM
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Update regarding this issue... borrowed a used PBCU from a SL 500 of the same model year; part # installed was the same as the one removed. With this unit installed the center vents worked properly. Reinstalled the original PBCU and the center vents again no longer opened. Connected the M-B HHT, went to activation mode and the vents again worked properly. Logical conclusion is that the fault lies with the PBCU.

Therefore ordered and installed a remanufactured unit from Beckmann Technologies. Installed that unit, ensured it was properly coded and... the center vents still don't work. Fault code check reveals no fault codes for this Beckmann PBCU.

Any suggestions as to how to resolve this problem? Checked with my local dealer and they are not interested in working on this vehicle, due to its age. Apparently they no longer have the original HHT in their tool inventory and they don't feel comfortable with the emulation mode present in the current SDS.

I could try a new PBCU from M-B, but that costs over $1,000 and there's no guarantee it will work.

Any suggestions???
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  #6  
Old 03-21-2017, 06:11 PM
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Ugh, I've been involved in problems that deify logic before. Did you send your old unit to Beckman for testing?

The vent flaps have position sensors ( potentiometers ) in addition to pots on the dash face to control air , I'd probe the voltages / look on the HHT at the values. I'm wondering if when run in manual HHT mode they are ignored but when run through the climate control buttons it cause a problem.

I'd also change the version coding to something else and check the results ( I don't think anything will "burn up" if this is done. Remember, this unit was also used on similar year C class. ( E class is different )

I've got 2 wiring diagrams of that area R23/1 though 3 are the vent flaps , r 1 through 3 are the dash knobs,

83 Climate control

83.40-U-2000YB Air conditioning (automatic) AC MY 1996

83.40-U-2000YC Air conditioning (automatic) AC As of MY 1997
Attached Thumbnails
R129 Automatic Climate Control Question-w83402000yb.jpg   R129 Automatic Climate Control Question-w83402000yc.jpg  
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  #7  
Old 03-21-2017, 06:34 PM
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I tried to post both complete diagrams but the board rejected the 2nd saying it was already posted. I then deleted the post but it still says it is already posted.
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  #8  
Old 03-23-2017, 12:43 AM
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The vehicle's original PBCU was sent to Beckmann for evaluation before purchasing the remanufactured unit. Nothing was found to be out of spec on that original unit; however, Beckmann did advise that their tests covers about 98% of the unit and the possibility exists that there is something they are missing. The reman unit that Beckmann sent was inspected and found to be fault free before shipping.

As for the flap actuators... the entire heater box, which includes, well, everything (including evaporator, heater core and flap actuators) was renewed with a new unit obtained from M-B. Installation of the heater box is basically just a plug and play procedure... with the exception of the evaporator and heater core temp sensors, nothing is transferred from the old heater box; all wiring harness connectors have a dedicated shape that cannot be installed in a wrong location. All vacuum line positions were carefully notated before removal of the original heater box; all lines were installed in their proper positions on the new heater box; proper positioning was reconfirmed using the factory line diagram.

The instrument cluster was inspected with the HHT and no provisions are available for changing the cluster's version coding.

As for the PBCU version coding using the HHT, the choices are simple: chassis choice of 201 or 129 and serial interface K1 and K2. All options have been tested, with no difference in results.

I'd gladly use the PBCU pulled from the donor SL but the LCD on that unit is damaged.

Thanks for the wiring diagrams; I'll check the voltages.
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  #9  
Old 03-23-2017, 06:48 PM
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Did the no flap control problem occur before or immediately after the heater box change?

I wonder if you car has 96 MY wiring and a 97 box was installed or the other way round.

Do you know the build date of the donor SL and what is your build date?
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  #10  
Old 03-27-2017, 10:17 PM
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The flap control problem was first evident following the installation of the new heater box. But... the vehicle had sat unused for about a year prior to installation of the new heater box and the PBCU was acting erratically for a period of time after the new heater box was installed, energized and brought back on line... the PBCU initially failed to respond to any commands. The unit became responsive again after the vehicle's battery had been reconnected for 24 hours. Beckmann explained the initial unresponsiveness as possibly being due to the fact the vehicle's battery had been disconnected for that year period and leak down of capacitors.

The vehicle in question is a 1997 SL 600, production date 12.96. The vehicle donating the PBCU is also a 1997, produced in 04.97. The M-B number for the PBCU was the same from both vehicles: 202 830 12 85. M-B does sub that number to a ... 13 85 and then to a ... 14 85 but Beckmann states the units are interchangeable.

I have been using the Star wiring diagram for a 1997 SL and have seen no discrepancies between the diagram and what is on the vehicle.

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