Checking Refrigerating Capacity (Short Test)
Checking refrigerating capacity (short test)
Conventional tools
2 thermometers -20 °C to +70 °C
Digital temperature measuring instrument with 4 measuring probes
Robbitemp (90020)
Air temperature measuring probe (90023)
Supplier, e.g.:
Switzerland: Kent-Moore (Europe) AG
P.O. Box, CH-6340 Baar
Germany: Kalte-Fischer
Postfach 266, Augsburger Str. 289 - 291
D-70327 Stuttgart
Digital temperature measuring instrument with 4 measuring probes
Therm (2263-2)
4-fold measuring point switchover switch (2235-4)
Air temperature measuring probe (W 453-5)
Supplier, e.g.:
Germany: Ahlborn Mes- und Regelungstechnik
Eichenfeldstr. 1-3,
D-83607 Holzkirchen
Note: Carry out test after minor repairs, prolonged disuse etc.
Test conditions
1 The vehicle should not be exposed to the sun before and during the test.
2 Check tension of the poly-V-belt for the compressor drive.
3 Check auxiliary fan function by switching on the ignition and shorting the two flat terminals on the pressure switch (S32 or S32/1). The auxiliary fan should start running at the 1st speed.
Then bridge the 2-pole coupling on the temperature switch (S25/4 or S25/5). The auxiliary fan 2nd speed should start up. Simultaneously observe the direction of rotation of the auxiliary fan (clockwise). On vehicles with 1- pole temperature switch (up to approx. 8/85), hold the 1-pole coupling to ground.
S25/4 Temperature switch 100/110 °C
Model 124.0 with 4-cylinder engine
S25/5 Temperature switch 105/115 °C
Model 124.0/2 with 6-cylinder engine
S25/4, S25/5 Temperature switch 100/110 °C and 105/115 °C
Models 124.1/3
4 Check fluid level in the air conditioner. To do so, pull off a cable on the pressure switch (S31/1), allow engine to run at idle speed (> 750/rpm) and switch on the automatic climate control with the function selection "lower vents". Clean the sight glass (arrow) in the fluid reservoir. Observe sight glass and reconnect the cable to pressure switch (S31/1) at the same time. Shortly before the electromagnetic coupling is switched on, the refrigerant should rise and subsequently flow through without bubbles (i.e. refrigerant no longer visible).
Caution! At pressures < 2 bar, the control for the refrigerant compressor is interrupted by the pressure switch (S31/1). The circuit is closed again when the pressure is > 0.6 bar above the switch-off pressure.
Note: If the refrigerant compressor is not switched on, bridge the cables to the pressure switch (S31/1) and check fluid level according to item 4. If the refrigerant compressor is still not switched on, check the compressor cut-out or the activation of the compressor.
Checking
1 Engage temperature selector wheel (A) in "MIN".
2 On the pushbutton switch (b), switch on the function selection "lower vents" and on the blower switch (c) the function selection "MAX"
3 Open the center and lateral nozzles and switch off switch (S24) (fresh air).
4 Insert a thermometer in the left or right center nozzle.
5 Provide a thermometer for ambient temperature (room temperature) approx. 2 m from the driver's side of the outside of the vehicle.
6 Open the window and close the vehicle doors. Run engine with approx. 2000/rpm.
Ta = Outside Temperature Deg C:
7 After approx. 5 minutes, read the air outlet temperature of the center nozzle and the outside temperature on the two thermometers and compare with the values in the diagram.
Note: If the refrigerating capacity is inadequate although the refrigerating compressor is operating, the suction/refrigerating capacity and high pressure of the air conditioner should be checked.
Caution! The air outlet temperature on the center nozzle must not be less than +5 °C. If the value is not attained, check the resistance value of the temperature sensor evaporator and its supply cables, renew temperature sensor if required, If no fault can be detected, renew control unit.