Checking Refrigerating Capacity & Suction/High Pressure
TESTING REFRIGERATING CAPACITY AND SUCTION/HIGH PRESSURE OF AIR CONDITIONING SYSTEMData
Difference between coldest and warmest outlet temperature max. 3°C
(cutting out/cutting in time of refrigerant compressor)
Coldest air outlet temperature out of center nozzle (center outlet) 3.5°C
Conventional tools
1 suction pressure gauge (1 bar vacuum to 10 bar gauge pressure)
1 high pressure gauge (0 - 40 bar gauge pressure)
2 thermometers (-20°C to +70°C)
1 hygrometer
Digital temperature measuring instrument with 4 measuring probes
Robbi temp 90020
Air temperature measuring probe 90023
(4.5 m cable length)
Supplier e.g.:
Switzerland: Kent-Moore (Europe) AG
P.O. Box, CH-6340 Baar
Germany: Fa. Kalte-Fischer
Postfach 266. Augsburger Str. 289-291
D-7000 Stuttgart 60
Digital temperature measuring instrument with 4 measuring probes
Therm 2263-2
Measuring point changeover switch with 4 connections 2235-4
Air temperature measuring probe W 453-5
(3m cable length)
Supplier e.g.:
Germany: Ahlborn Mes- und Regelungstechnik in der Eichenteldstrase 1-3, D-8150 Holzkircher
Functional test
In the event of complaints on air conditioning system or fo- trouble diagnosis.
For a checkup in workshop in the event of complaints owing to insufficient cooling capacity or for a trouble diagnosis on air conditioning systems, proceed according to test method applicable for ambient temperatures from +20 °C to +40 °C. All test values can be read after 10 minutes constant operation.
Test conditions
1 The vehicle sh6uld not be in the sunlight during test.
2 Check tension of V-belt for compressor drive.
3 Check auxiliary fan for function, while switching on ignition and bypassing the two flat plugs on pressure switch (19), or connecting 1-pin connector of 100 °C switch to ground. Pay attention to direction of rotation of auxiliary fan (clockwise).
4 Check fluid level in air conditioning system; for this purpose, pull one line from pressure switch (22), run engine at idle (>700/min) and engage air conditioning system by means of function selection "max dehumidification". Clean sight-glass (arrow) in receiver drier. Watch sight-glass while simultaneously plugging line on pressure switch (22). Refrigerant should rise shortly after switching on electromagnetic clutch and should then flow free of bubbles (i.e. refrigerant no longer visible).
Attention! In the event of major refrigerant losses or an empty system, the voltage for the refrigerant compressor is interrupted by the pressure switch (22). When the pressure increases to 0.6 bar above the cutout pressure, the circuit is again closed.
5 Check whether the heater shuts off in selector wheel position "MIN". For this purpose, let engine run at idle and engage air conditioning system with function selection "normal A/C". Refrigerant compressor should be on after 20 seconds at the latest.
Note: If the refrigerant compressor is not engaging, bridge lines from pressure switch (22) and check fluid level according to item 4. If the refrigerant compressor is still not engaging, test entire system with socket box and volt-ohmmeter, refer to 83-039. On model 201.024 starting model year 85 and on model 201.122 there may be an additional fault on compressor cutout.
Testing
1 Set temperature selector wheel (a) to "MIN".
2 Switch on function selection "center vents" of pushbutton switch (b) and function selection "max dehumidification" of switch air conditioning system (c).
3 Set blower switch (15) to 4th blower stage.
4 Open center and side outlets and switch off switch (26) (fresh air).
5 Insert one thermometer into lefthand or right- hand center outlet.
6 Position one thermometer for ambient temperature (room temperature) approx. 2 m from driver's side.
7 Place a hygrometer into tray of center console.
8 Unscrew closing caps (1). Then connect hose line of suction pressure or high pressure gauge to service valves. Make sure that the connecting nipple of the hose lines has a pressure pin in center.
1 Closing cap of Suction line on all models
9 Open window and close vehicle doors.
1 Closing cap on pressure line engine 102 up to model year 84
1 Closing cap on pressure line engine 601 and engine 102 starting model year 85
13 Pull 1-pin connector from temperature switch 100°C (16) and connect to ground, so that the auxiliary fan runs along during entire test procedure.
16 Temperature switch 100 °C engine 102 up to model year 84
16 Temperature switch 100 °C engine 102 starting model year 85
16 Temperature switch 100 °C engine 601 up to model year 84
16 Temperature switch 100 °C engine 601 starting model year 85
14 Run engine at approx. 2000 rpm.
15 After operating engine for approx. 10 minutes, read values on thermometers and pressure gauges, as well as on hygrometer.
Note: Specified values, refer to diagram, are max. values and must not be exceeded.
16 Check intake and high pressure in dependence of ambient temperature, using the diagrams for this purpose. Also check air outlet temperature (mean value of two cold air outlet temperatures) also according to diagram values. (The difference between the coldest and the warmest outlet temperature should not be higher than 3 °C). Check temperature sensor, if required, renew, or connect new pushbutton switch unit for a tryout.
Diagram for mode 201.024
1) Relative humidity
Ta Outside temperature (°C)
A Air outlet temperature (°C)
B Pressure in front of compressor (bar)
C Pressure following compressor (bar)
D Coolant temperature (°C)
Diagram for mode 201.122
1) Relative humidity
Ta Outside temperature (°C)
A Air outlet temperature (°C)
B Pressure in front of compressor (bar)
C Pressure following compressor (bar)
D Coolant temperature (°C)
17 Check cutout temperature, setting blower switch (15) to stage 1 for this purpose. Run engine at approx. 2000 rpm. Following 3rd cutout of electromagnetic clutch the air outlet temperature at center outlet should not be less than approx. +3.5 °C.
Note: If the respective value is less than specified, check temperature sensor of air conditioning system and renew, if required, or test electric lines from temperature sensor of air conditioning system to pushbutton switch unit for ground short. If there is no remedy, renew pushbutton switch unit.
18 Take hose lines from service valves and close service valves again with closing caps.
19 Plug 1-pin connector to temperature switch 100°C (16).
20 Remove thermometer and hygrometer from vehicle.