4-22. AIR SYSTEM - Continued
Raise drier and install on frame using capscrews (2) and locknuts (3).
Connect air lines to drier. Be sure they are connected as noted in REMOVAL preceding.
Connect wire (1) to terminal of heater.
Connect the batteries and start the main engine. Allow pressure to build up to governor cut-out. Shut main
Wait two minutes and observe the primary air pressure gage in the cab if this pressure continues to drop,
check for air leakage from the drier purge valve. If air is leaking, this indicates a failed check valve in the
outlet port of the air drier. Replace check valve as detailed in REPAIR following.
Restart main engine and drain air from the primary air tank until the compressor restarts compressing.
Check for excessive leakage from the purge valve by brushing the purge valve with soap solution. Brush all
Replace/tighten fittings as required or replace purge valve as detailed in REPAIR following.
Check operation of the drier safety valve by pulling on exposed stem. Air must exhaust while the stem is
held and should reseat when released. Replace as detailed in REPAIR following if test is unsatisfactory.
Check that, when ignition is on, the heater terminal is at 12 volts with respect to the drier shell. If not, check
breaker behind hinged dash panel and wire between breaker and drier.
Turn the ignition switch off and cool the end cover assembly to less than 40 deg. F (4 deg. C). With an
ohmmeter check resistance between electrical terminal and the aluminum of the end cover. Resistance
should be 2.0 - 4.0 ohms.
Warm the end cover to over 90 deg. F (32 deg. C) and check resistance as above. Resistance should
exceed 1000 ohms.
If the resistance is outside these limits, carry out test 15, 16, and 17.
With the ignition switch off, remove the thermostat cover by removing screws.
Check resistance between aluminum of the end cover and heater post. If not between 2.0 - 2.8 ohms
replace the end cover assembly as detailed in REPAIR following (the heater has failed but cannot be
replaced alone). If the heater resistance is within these limits, the thermostat has failed. See REPAIR
Run the truck as normal and check for moisture build up in the tanks daily. Replace desiccant if there is
evidence of moisture in the air tanks.