Operational and Leakage Tests
rv mm 42.02.000
- Check all lines and fittings leading to and from the air dryer for leakage and integrity. Repair any leaks found.
- Build system pressure to governor cutout and note that the dryer purges with an audible escape of air. Watch the system pressure and note the pressure fall-off for a 10-minute period. If the pressure drop exceeds 1 psi/minute from either service reservoir, inspect the vehicle air systems for sources of leakage and repair them. Refer to troubleshooting information in Bendix or Haldex service literature.
- Check for excessive leakage around the purge valve with the compressor in the loaded mode (compressing air). Apply a soap solution to the purge valve exhaust port and observe that leakage does not exceed a 1-inch (25-mm) bubble in 1 second. If the leakage exceeds the maximum specified, refer to troubleshooting information in the Bendix or Haldex service literature.
- Build system pressure to governor cutout and note that the dryer purges with an audible escape of air. Fan the service brakes to reduce system air pressure to governor cut-in. Note that the system once again builds to full pressure and is followed by a dryer purge. If the system does not follow this pattern, refer to troubleshooting information in the Bendix or Haldex service literature.
- Check the operation of the end cover heater and thermostat
assembly during cold weather operation as follows:
- Electric Power to the Dryer: With the ignition in the ON position, check for voltage to the heater and thermostat assembly using a voltmeter or testlight. Unplug the electrical connector at the air dryer and place the test leads on each of the connections of the female connector on the vehicle power lead. If there is no voltage, look for a blown fuse, broken wires, or corrosion in the vehicle wiring harness. Check to see if a good ground path exists.
- Thermostat and Heater Assembly Operation: These tests are
not possible except in cold weather operation. Turn off the ignition
switch and cool the thermostat and heater assembly to below 40°F
(4°C). Using an ohmmeter, check the resistance between the electrical
pins in the air dryer connector half. The resistance should be 1.5
to 3.0 ohms for the 12-volt heater assembly and 6.0 to 9.0 ohms for
the 24-volt heater assembly.
Note: Some models of the AD–9 may have a resistance reading of 1.0 to 2.5 ohms.
Warm the thermostat and heater assembly to approximately 90°F (32°C) and again check the resistance. The resistance should exceed 1000 ohms. If the resistance values obtained are within the stated limits, the thermostat and heater assembly is operating properly. If the resistance values obtained are outside the stated limits, replace the heater and thermostat assembly.
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