Testing Cooling Capacity (Short Test)
"Refrigerant CapacityTESTING COOLING CAPACITY (SHORT TEST)
as of 09/85
Test Conditions:
Refer to parts 1 to 4
Difference between coldest and warmest outlet temperature:
Measured between cutout and cut-in of refrigerant compressor max. 3 °C
Coldest Outlet Temperature At Center Outlet:
Measure, + 5 ± 1 °C with selector engaged at MIN and function selections "Normal ventilation" and "Blower max."
Commercially Available Tools:
2 thermometers
- -20 °C to +70 °C
Digital temperature measuring instrument with 4 test probes
- robbi temp 90020
- Air temperature measuring probe 90023 (cable 4.5 m long)
Supplier e.g.:
Switzerland: Kent-Moore (Europe) AG
P.O. Box, CH-6340 Baar
Germany: Kalte-Fischer
Postfach 266, Augsburger Str. 289-291
D-7000 Stuttgart 60
Digital temperature measuring instrument with 4 test probes
- Therm 2263-2
- 4-point changeover switch 2235-4
- Air temperature measuring probe W453-5 (cable 3 m long)
Supplier e.g.:
Germany: Ahlborn MeB- und Regelungstechnik,
Eichenfeldstr. 1-3,
D-8150 Holzkirchen
Note: Perform test after minor repairs, lengthy idle periods or similar.
Test Conditions:
1. The vehicle must not be left in direct sunlight prior to or during the test.
2. Check tension of V-belt or poly V-belt for compressor drive.
3. Check function of auxiliary fan by switching on ignition and shorting the two flat plugs on pressure switch (S32 or S32/1). Auxiliary fan must run in 1st stage.
Then bridge 2-pole coupling at temperature switch (S25/3 or S25/5). Auxiliary fan must run in 2nd stage. At the same time, watch direction of rotation of auxiliary fan (clockwise). In vehicles with 1-pole temperature switch (up to approx. 8/87), route 1-pole coupling to ground.
S25/5 105/115 °C temperature switch in vehicles with 6-cylinder engine
S25/3 110 °C temperature switch in vehicles with 6-cylinder engine
In vehicles as of 09/87 with coolant temperature sensor B 11/7 or B 10/8, disconnect and bridge 2-pole coupling at temperature sensor. At outside temperatures > 25 °C, the auxiliary fan immediately starts in the 2nd stage when the coupling is disconnected.
B 11/7 Coolant temperature sensor, engine 116/117
4. Check fluid level in air conditioner:
To do this, disconnect one cable at pressure switch (S 31/1). run engine at idle (>750 rpm) and switch on automatic climate control with function selection B Clean sight glass (arrow) in fluid tank. Watch sight glass and simultaneously replace cable on pressure switch (S 31/1). Shortly after the electromagnetic clutch switches on, the refrigerant should rise and then flow through without bubbles (i.e. refrigerant no longer visible).
Caution! In the event of large refrigerant losses or an empty system. the voltage for the refrigerant compressor is interrupted by pressure switch S31/1. The current circuit is closed again when the pressure rises to 0.6 bar above the cutout pressure.
Note: If the refrigerant compressor fails to cut in. bridge cables from pressure switch (S 31/1) and check fluid level as described in para. 4. If the compressor still fails to cut in, test the compressor cutout.
Testing:
1. Engage temperature selector (a) at "MIN".
2. On pushbutton switch (b) select function B and on blower switch (c) select function D
3. Open center and side outlets and switch off switch (S 24) (fresh air).
4. Insert a thermometer into the left-hand or right- hand center outlet.
5. Position a thermometer for the ambient temperature (room temperature) outside the vehicle approx. 2 m from the driver's side.
6. Open windows and close doors. Run engine at approx. 2000 rpm.
7. After approx. 5 minutes. read off air outlet temperature at center outlet and outside temperature on the two thermometers and compare with the values in the graph.
Graph:
Ta Outside temperature °C
Note: If the system provides no cooling capacity although the refrigerant compressor is running, test the suction/cooling capacity and high pressure of the air conditioner (section "Refrigerant Capacity" above).
Caution! The air outlet temperature at the center outlet must not be less than + 5 °C. If the temperature drops below or fails to reach the specified level, test the resistance of the evaporator temperature sensor and its cables, and replace temperature sensor if necessary. If no fault can be detected, replace control unit.