Checking the Air Dryer

sb mm 42.02.001

During cold-weather operation, check the operation of the end cover heater and thermostat assembly.

  1. With the ignition switch in the ON position, check for voltage to the heater and thermostat assembly. Unplug the electrical connector at the air dryer, and place the test leads of a voltmeter on each of the pins of the male connector. If there is no voltage, look for a blown fuse, broken wires, or corrosion in the vehicle wiring harness. Check that a good ground path exists.
  2. Check the thermostat and heater operation. Turn the ignition switch to the OFF position and cool the end cover assembly to below 40°F (4°C). Using an ohmmeter, check the resistance between the electrical pins in the female connector. The resistance should be 1.5 to 3.0 ohms for the 12-volt heater assembly.
    Warm the end cover assembly to over 90°F (32°C) and again check the resistance. It should exceed 1000 ohms. If it does, the thermostat and heater assembly is operating properly. If it does not, replace the purge-valve housing assembly, which includes the heater and thermostat assembly.
Note:
Parent topic: Brakes
Document Number: 0000120410
Manual Publication Date: 2025-01-08
Topic Publication Date: 2024-11-18