Test Conditions

AIR CONDITIONING, CHECKING COOLING CAPACITY, (BRIEF TEST)






Test Conditions:
Observe numbers 1 through 4.

Differential Between Coldest And Hottest Exit Temperature:
Measured between cut-in and cut-out of a/c compressor:
Max. 3 °C

Coldest Air Exit Temperature, From Center Vent:
Measure +5 ± 1 °C both selector wheels clicked into MIN position






Switch ON air conditioning by selecting (image)






Set air volume switch to stage 4 and air distribution switch to the symbol (image)

Commercially Available Tools





4 probe digital thermometer:
Robbi temp 90020
Air temperature probe 90023
(4.5 m cable length)
Supplier, e.g.:
Switzerland: Kent-Moore (Europe) AG
Postfach, CH-6340 Baar
Germany: Kalte-Fischer
Postfach 266
Augsburger Strasse 289-291
D-7000 Stuttgart 60






4 probe digital thermometer:
Therm 2263-2
4-way position switch 2235-4
Air temperature probe W453-5
(3m cable length)
Supplier, e.g.:
Germany: Ahlborn Mess und Regelungstechnik
Eichenfeldstr. 1-3
D-8150 Holzkirchen

NOTE: Perform test when air conditioning/automatic climate control operation is unsatisfactory and/or for fault diagnosis.

Test Conditions:
1. The vehicle must not be left in the sun prior to or during testing.
2. Check tension on a/c compressor V-belt.
3. Check operation of auxiliary fan by switching on ignition and shorting across the two flat connectors on the pressure switch (S32/1). The auxiliary fan must then run at stage 1.

Continue by running a jumper across the 2-pin coupling on the temperature switch (S25/2) or by connecting the 1-pin coupling (S25/3) to ground. Auxiliary fan must run at stage 2. At the same time, note the direction in which the auxiliary fan rotates (clockwise).






S32/1 Auxiliary fan pressure switch
20 bar on
15 bar off






S25/5 105/115 °C temperature switch on vehicles with 8-cylinder engine






S25/3 110 °C temperature switch on vehicles with 6-cylinder engine






4. Check the fluid level in the air conditioning system:






Remove one wire from the pressure switch (S31/1), let the engine run at idle (>750 rpm) and switch on the air conditioning by selecting button (image). Clean sight glass (arrow) in receiver dehydrator. Observe sight glass while simultaneously reconnecting wire at pressure switch (S31/1). The refrigerant must begin to rise soon after the electromagnetic clutch switches on. Then it must start to flow with no bubbles visible (that is, the refrigerant is no longer visible).

Caution! Where a substantial loss of refrigerant is present, or the system is empty, the pressure switch (S31/1) interrupts the current to the a/c compressor. The circuit closes again when the pressure rises to more than 0.6 bar above cut-off pressure.

NOTE: If the a/c compressor fails to switch on, run a jumper between the wires from the pressure switch (S31/1) and check fluid level as described under number 4. If the a/c compressor still fails to switch on, check the compressor cut-off and the a/c compressor control.