A/C System Service Procedures (83/50)

Publication date: 1987-10-01
Reference number: 83/50
Supersedes refnos: 83/25

A/C SYSTEM SERVICE PROCEDURES

TECHNICAL SERVICE BULLETIN

Reference Number(s): 83/25, 83/50, Date of Issue: October 1987
Superceded Bulletin(s): 83/50, Date of Issue: June, 1985

WORKING ON THE AIR CONDITIONING SYSTEM

Model(s): All 1983-88 Mercedes-Benz Models

Group: Air Conditioning & Heating

Bulletin No.: 83/25

Date: October 1987

NOTE: This bulletin supersedes Service Bulletin 83/50, dated June, 1985.

SERVICE INFORMATION

When working on the air conditioning section of the climate control system, be sure to adhere to the following procedures:

SERVICE PROCEDURES

CHECKING RECEIVER-DRIER FLUID LEVEL

The fluid level of the receiver-drier must be checked as follows during inspection and each scheduled maintenance.

Clean sight glass on receiver-drier.
Pull off one wire from the pressure switch.
Idle engine and engage the A/C compressor from the pushbutton control panel.
Watch sight glass and re-attach wire to pressure switch at the same time.

Shortly after the A/C compressor clutch switches on, the fluid level must rise, and the refrigerant should flow past the sight glass free of bubbles (i.e., the refrigerant will not be visible).

If bubbles are present, check system for leaks using Refrigerant Leak Detector (see Section G). Seal and charge system with R12 refrigerant.

MODIFIED REFRIGERANT CAPACITIES

NOTE: When servicing a vehicle observe the refrigerant capacities.

REFRIGERANT CAPACITIES

Model	R12 Refrigerant, kg.
107	1.0
123	1.3
124	1.1
126	1.3
201.02/.12	1.0
201.034	0.95

REPLACING THE RECEIVER-DRIER

The receiver-drier is to be replaced whenever the refrigerant system is exposed to the atmosphere.

If moisture in the atmosphere is allowed to enter the refrigerant system, it may saturate the receiver-drier.

REPLACING COMPRESSOR

If the compressor is replaced due to internal damage (e.g., seized or damaged valve plates, etc.), it is mandatory to replace components as outlined in the chart.

Fig 1: REPLACEMENTS TABLE

NOTE: Flushing the A/C system is prohibited.

IMPORTANT: Do not replace refrigerant lines on systems with York compressors. Instead, install strainer (part no. 000 131 04 34) in the suction connection according to job no. 83.7-524/2.

Refill the system with the correct amount of refrigerant oil. After replacing components, check suction and discharge pressures of the system.

In addition, check auxiliary fan function via:

Temperature switch (52°C) or
The high pressure switch (20 bar) and via the coolant temperature switch (100°C). Be sure to check proper direction of rotation: (clockwise).

For engines 102 and 601, check function of electromagnetic fan clutch.

CAUTION: A defective expansion valve will lead to compressor failure because:

Liquid refrigerant could reach the compressor, resulting in fluid lock due to excessive suction pressure.
Overheating of the compressor could result due to insufficient suction pressure (possibly even a vacuum) if the expansion valve is clogged.

TESTING EXPANSION VALVE

Replacement of the expansion valve, for reasons other than those described in Sections C and D, should only be done after the following tests have been performed.

Perform Output Testing
If after completion of testing:
1. Suction pressure is too High
2. Discharge pressure is too Low
3. Air temperature at center outlet is too High
4. Condensation forms on the suction hose and evaporator the expansion valve may be stuck open. Replace expansion valve.
If after completion of Testing:
1. Suction pressure is too low
2. Discharge pressure is too Low
3. Air temperature at center outlet is too high
4. Condensation forms on the suction hose and evaporator the expansion valve may be stuck closed. Replace expansion valve.

IMPORTANT: When performing the Output Test use the performance charts in Section J of this Service Information.

CHARGING THE SYSTEM

Whenever the compressor is replaced due to a failure, keep all parts extremely clean to avoid contaminating the system with any foreign particles. Always cap off all connection fittings until they are ready to be reconnected.

When charging the system, it is very important to follow the equipment manufacturer's instruction. The correct refrigerant fill quantity or charge can only be achieved by weighing the refrigerant or by use of automatic refrigerant charging equipment.

IMPORTANT: Never charge the system by only observing the level in the sight glass. The sight glass should only be used as an indicator to verify function of the A/C system as described in CHECKING RECEIVER-DRIER FLUID LEVELS.

EQUIPMENT INFORMATION

Equipment Name*	Manufacturer/Model No.
Refrigerant leak detector	Kent-Moore/J29547
Air conditioning evacuating	Kent-Moore/J23500-01
and recharging system	Draf/1250
*Available through MB Standard Equipment Program SUN/474

NOISE-RELATED COMPLAINTS

For complaints concerning noise with the compressor switched on, check function of the expansion valve. If the compressor is seized, proceed according to the chart in Section D.

BELT DRIVE: POLY-V-BELT

Vehicles which have engines equipped with the single poly-V-belt should be additionally inspected. If severe slippage of the belt occur, this will cause the A/C compressor to disengage. It is therefore important to inspect the belt for wear and proper tension. It is also important that the belt be free of contaminants such as oils and engine coolant.

For additional information regarding belt slippage, refer to S.I. MBNA 83/22 for Model 124.030 and S.I. M3NA 83/20a for Model 201.024.