Modifications To The A/C System (83/79)
Publication date: 1994-12-01Reference number: 83/79
MODIFICATIONS TO THE A/C SYSTEM
TECHNICAL SERVICE BULLETIN
MODEL 140 MODIFICATIONS TO THE A/C SYSTEM
Model(s): 1993 Mercedes-Benz 300 SD, 300 SE, 400 SEL, 500 SEC, 500 SEL, 600 SEC, 600 SEL; 1994-on Mercedes-Benz S 320, S 350, S 420, S 500, S 600
Group: 83 - Climate Control
Bulletin No.: 83/79
Date: February 1994
A. AIR FLAPS AND AIR FLAP ACTUATION
As of April 1993, bowden cables have replaced the previously used flex cables to actuate the center and side air vents, allowing a precise and play-free actuation of the air flaps. See Fig 1 and Fig. Fig 2 .
Removal/installation procedures for the center and side outlet knurled knob panel remain unchanged.
B. NOISE REDUCTION
As of April 1993, the blower motor is attached to its bracket using rubber mounts, thereby isolating any vibration and reducing resultant noise. The support for the heater box between the defroster ducts at the cross brace has been eliminated.
The vacuum elements for the left and right side air outlet diverter flaps (39 and 40, Fig. Fig 3 ) have been eliminated and as a result are not available as replacement parts (See vacuum diagram, Fig. Fig 6 ).
For an interim time period, heater boxes with closed-off openings (10, Fig. Fig 4 ) for the vacuum elements were installed in production.
The switchover valve block (Y11, Fig. Fig 5 ) was modified by eliminating the connection (5) for the vacuum elements (39, 40, Fig. Fig 3 ). As a result, the side air outlet diverter flaps are without function thereby allowing air to travel through the evaporator and heater core, and to the side outlets at all times.
C. BLOWER REGULATOR
The blower regulator (A32n1, Fig. Fig 7 ), part no. 005 820 50 10, is now available as a replacement part.
For the rear A/C system in Model 140.134, a diode (5, Fig. Fig 8 ) is installed between the rear A/C blower motor (M2/1) and the blower regulator (N29/2) to ensure shut-off.
D. AUXILIARY FANS
As of chassis end number 1A 123446, the auxiliary fans are in switched 2 stages (previously 3 stages).
| Description | 1st Stage | 2nd Stage |
|---|---|---|
| Refrigerant pressure bar | 16 On 13 Off | 20 On 17 Off |
| Engine coolant temperature sensor (B10/8) °C | 100 On 95 Off | 115 On 107 Off |
| Voltage supplied to auxiliary fans V | 9 | 12 |
The revised A/C pushbutton control module (N22) recognizes if 2-stage or 3-stage auxiliary fans are installed.
A DTC code of 98 and 99 may be stored in the A/C pushbutton control module (N22) in isolated cases. However, these codes should be ignored provided the auxiliary fans operate properly in both stages.
Refer to Fig. Fig 9 for location of preresistors (R15 and R15/1) with two stage auxiliary fans, and connector bridge between resistors (arrow). Refer to Fig. Fig 10 for location of preresistors (R15 and R15/1) with three stage auxiliary fans.
E. REAR A/C SYSTEM
As of January 1993, an improved rear refrigerant shut-off valve (Y67, Figs. Fig 11 and Fig 12 ) is used in production for noise reduction. It is recognized by a different manufacturer part no. (ND 113 300- 1541, previously 1540).
As of chassis end number 1A 128374, the refrigerant injection valve (107, Fig. Fig 11 ) is no longer installed in the evaporator (13) for noisereduction. However, a modified refrigerant injection valve (108) is installed into the rear refrigerant shut-off valve (Y67, Fig. Fig 11 and Fig. Fig 12 ).
The pressure line (12, Fig. Fig 11 ) has been insulated to reduce the cooling loss (heat transfer) to a minimum.
As of August 1993, a revised rear tunnel flap vacuum valve (Y67/1, Fig. Fig 13 ), part no. 140 800 14 78, is installed for noise reduction.