Checking Refrigerating Capacity & Suction/High Pressure

DATA
Max difference between coldest and 3 °C
warmest outlet temperatures
(switching off/on time of
refrigerant compressor)

Coldest air outlet temperature 3.0 °C
from center outlet








Conventional tools







Digital temperature measuring instrument with 4 measuring probes


Robbi temp 90020
Air temperature measuring probe 90023
(cable length 4.5 m)


Supplier:
Switzerland: Kent-Moore (Europe) AG
P.O. Box, CH-6340 Baar
Germany: Kalte-Fischer
Postfach 266, Augsburgerstr. 289-291
D-7000 Stuttgart 60







Digital temperature measuring instrument with 4 measuring probes


Therm 2263-2

4-point measurement
changeover switch 2235-4

Air temperature measuring probe W453-5
(cable length 3 m)


Supplier:
Germany: Ahlborn MeB- und Regelungstechnik,
EichenfeldstraBe 1 - 3,
D-8150 Holzkirchen


Test conditions
1 The vehicle must not be exposed to direct sunlight either before or during the test.
2 Check tension of ribbed V-belt for compressor drive.







3 Check function of auxiliary fan by switching on ignition and shorting the two plugs at the pressure switch (S32).

- In vehicles with small auxiliary fan,
the auxiliary fan and the engine fan should operate.







S25/4 100/110 °C temperature switch in models 201.024 (AUS),(J) and 201.028







S25/5 105/115 °C temperature switch
in model 201.034/035







S25/5 105/115 °C temperature switch
in model 201.029







S25/5 105/115 °C temperature switch
in models 201.126 and 201.128


- In vehicles with large auxiliary fan
and 4-cylinder engine, the auxiliary fan should operate (except models 201.024,(AUS),(J) model year 85).
In vehicles with 5 and 6-cylinder engine, only the auxiliary fan should operate in the 1st stage. For models 201.024 (AUS), (J) and 201.028/034, then connect the 1-pole coupling at temperature switch S25/4 or S25/5 to positive. For models 201.029/034/035 ECE/CAT/126 and 128, bridge the 2-pole coupling at temperature switch S25/4 or S25/5. Auxiliary fan must operate in the 2nd stage.
At the same time, observe the direction of rotation of the auxiliary fan (clockwise).







4 Check fluid level in air conditioning system:
To do this, disconnect one cable at the pressure switch (S31/1), run engine at idle speed (> 750 rpm) and switch on air conditioning system. Clean sight glass (arrow) in receiver dehydrator. Observe sight glass and simultaneously connect cable to pressure switch (S31/1). Refrigerant level must rise shortly after the electromagnetic clutch is switched on and then flow through with no bubbles (i.e. refrigerant no longer visible).


!
In the event of severe refrigerant loss or an empty system, the voltage for the refrigerant compressor is interrupted by the pressure switch (S31/1). The power 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 the cables from the pressure switch (S31/1) and check the fluid level in accordance with paragraph 4. If the refrigerant compressor still fails to cut in, check the compressor cutout (section A)Testing and Inspection or the actuation of the compressor.


Checking







1 Heater switches (22 and 23) at position "O".
2 Set air distributor switch (24) to symbol [][] and air volume slide switch (53) to the 4th blower stage.
3 Move temperature slide control (N19) to "max" and move lever (19) upwards to symbol[][].
4 Open left and right side outlets and switch on recirculated air switch (S24).
5 Insert a thermometer into the left or right center outlet (25).
6 Position a thermometer for the ambient temperature (workshop temperature) outside the vehicle approx. 2 m from the driver's side.







7 Unscrew closing caps (arrows). Then connect hose lines of suction pressure or high-pressure gauge to the service valves. Ensure that the connecting nipple of the hose has a thrust pin in the center.
8 Open windows and close vehicle doors.







S25/4 100/110 °C temperature switch, engine 102







S25/4 100/110 °C temperature switch, engine 601


9 In vehicles with 4-cylinder engine, disconnect 2-pole coupling from 100/110 °C temperature switch (S25/4) and bridge so that the electromagnetic clutch of the engine fan runs during the entire test sequence.
10 Run engine at approx. 2000 rpm.
11 After approx. 10 minutes, take readings on the thermometers and pressure gauges.


NOTE: The specified values are maximum values and must not be exceeded.


Check pressures upstream and downstream of the compressor (low pressure and high pressure)







Low pressure High pressure
Normal Normal


Refrigerant circuit in order







Low pressure High pressure
Too low Normal or too low


Possible cause:
Insufficient refrigerant in the system. Expansion valve blocked. Receiver dehydrator blocked. Evaporator iced up. Evaporator soiled.








Low pressure High pressure
Too high Normal


Possible cause:
Expansion valve injecting too much refrigerant.








Low pressure High pressure
Too high Too low


Possible cause:
Compressor faulty. Valves in compressor faulty.







Low pressure High pressure
Too high Too high


Possible cause:
Too much refrigerant in the system. Condenser soiled. Auxiliary fan failed or rotating in wrong direction. Engine fan failed.


13 Check cutout temperature of temperature slide control by moving air volume slide switch to stage 1. Run engine at approx. 2000 rpm. Alter the 3rd cutout of the electromagnetic clutch, the air outlet temperature at the center outlet should not be less than approx. +3 °C; check evaporator temperature sensor if necessary.
14 Check pressure limiting of expansion valve by:
Switching off the engine and observing the suction pressure gauge. The suction pressure should rise only very slowly and not exceed 3.5 bar within approx. 3 minutes; if necessary, renew expansion valve and repeat test from paragraph 11 onwards.
15 Disconnect hose lines from service valves and seal service valves again with closing caps.
16 In vehicles with 4-cylinder engine, connect 2- pole coupling to 100/110 °C temperature switch (S25/4).
17 Remove thermometers from vehicle.