Roof-top air-conditioning system CC8 6 Maintenance
605
6.8 Post-repair procedures and testing
6.8.1 Check refrigerant pressures and pressure switches function tests
1. General
Every air-conditioning system filled with refrigerant is in a state of overpressure, which is equal throughout the
system circuit and which depends on ambient temperature.
During operation of the system, the working pressure on the intake side differs from that on the delivery side of the
compressor. The pressures differ and are influenced by the compressor operating speed, the temperature inside
the vehicle, the outside air temperature and relative humidity. Abnormal working pressures indicate that there is a
fault in the system.
Working pressures should be checked at a compressor speed of approx. 3000 rpm and an air temperature between
20 °C and max. 35 °C. The fan must be operated at full power, stage 3. The hood must be fitted for pressure testing
and for functional testing of the pressure switches, as the application of air to the heat exchangers has a decisive
influence for obtaining the operating pressures.
The following operating pressures must be obtained with the compressor in operation:
If different pressure values are obtained, an authorized repair shop must be consulted to investigate the reasons.
When the pressure test is complete, disconnect the pressure gauges and refit the sealing caps.
2. High pressure switch test:
– Connect pressure gauges to system.
– Remove fuse (F1 and F2) of condenser fan and fit hood.
– Run engine at medium engine speed and switch on air-conditioning system.
– Check whether compressor switches off at a pressure of 22.5 ± 2 bar.
– Remove hood and refit fuse of condenser fan.
– Check that compressor switches on again when pressure drops to 20 ± 2 bar.
3. Perform complementary steps.
CAUTION
If the high pressure switch is not working properly, switch off the air-conditioning
system immediately, as refrigerant will be discharged via the pressure relief valve as
soon as the pressure reaches 34.5 bar.
Outside air temperature Low pressure gauge High pressure gauge
20 °C 2.0 bar abs ± 0.2 bar 10 bar abs ± 2 bar
25 °C 2.1 bar abs ± 0.2 bar 12 bar abs ± 2 bar
30 °C 2.3 bar abs ± 0.2 bar 14 bar abs ± 2 bar
35 °C 2.7 bar abs ± 0.2 bar 16 bar abs ± 2 bar
To Next Page
Loading...
