A/C - Center Housing Replacement, ACC Servo Assembly
REF. NO. MBNA 83/38TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: February, 1983
SUBJECT:
REPLACING CENTER HOUSING OF ACC SERVO ASSEMBLY MODELS 107, 116 and 123
Complaints of coolant loss due to leakage at the servo center housing, can be repaired by installing a new center housing and seal kit.
IMPORTANT:
Before starting to rebuild servo unit, pressure test cooling system to verify that the leakage is at servo unit and not at hose connections.
Check coolant for proper antifreeze protection (-22~F - 30~C). If required, add approved antifreeze to obtain proper protection, after above test.
Rebuilding Procedure (Servo in Park Position)
1. Remove servo assembly.
2. Remove supply/return coolant housing by removing four screws.
3. Remove compression spring (8) and gasket (7). Discard old gasket (Figure 3).
4. Carefully lift up center housing (2) just enough to insert a thin pair of pliers to hold the poppet valve stem securely.
5. While a helper holds valve stem securely, pry poppet valve from stem using two screwdrivers.
NOTE:
The poppet valve stem must be held down to prevent bending the stem or carrier spring.
Alternate Method:
The poppet valve can be carefully cut off its stem with small side-cutting pliers.
CAUTION:
Do not damage stem of poppet valve, a new part is not included in kit.
6. Remove center housing and gasket
7. Remove snap ring flat washer(s) and lip seal.
NOTE:
If the old seal is red and 2 flat washers were used, discard the smaller and re-assemble with only the larger washer.
IMPORTANT:
Do not turn servo valve shaft while replacing lip seal as this will change the internal calibration of the unit.
8. Assemble new parts, center housing (2), gaskets (3) & (7), seal (4) and poppet valve (6) in reverse order (Figure 6).
NOTE:
Install seal with lip facing up as shown in Figure 6. Silicone spray on valve stem will aid in installing new poppet.
IMPORTANT:
Be sure the valve stem for the poppet is positioned back into the housing bore (5) before securing the housing (1) the stem will be bent.
9. Fasten housing with 4 new screws and spring lock washers from kit. Tighten screws in small steps to a final torque of 1.5 N-m (13 lb.in.).
NOTE:
Install spring washers as shown in Figure 7.
10. Install servo assembly into car and refill cooling system.
11. Pressure test cooling system.
12. Run engine to operating temperature at 2000 rpm with DEFROST ON to speed bleeding air from cooling system.
13. Check for normal coolant temperature, heater output and correct coolant level.
NOTE:
Coolant must always be a sufficient mix of approved antifreeze and water, to insure protection to - 22~F (-30~C) for all regions of North America YEAR-ROUND without exception (corrosion and boil-over protection). Plain water usage can contribute to a repeat failure.