Bendix Commercial Vehicle Systems AD-4 AIR DRYER 10/04 - Manual (Page 6)

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resistance should be 2.0 to 4.0 ohms for the 12 volt,
60 watt end cover and 4.0 - 7.0 ohms for the 24 volt,
120 watt end cover. These resistance values apply
to either single or dual terminal air dryer end covers.
Warm the end cover assembly to over 90 degrees
Fahrenheit and again check the resistance as above.
The resistance should exceed 1000 ohms for both
single and dual terminal air dryers. 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, proceed to Step C to determine the
cause.
C. Heater Element Inspection
With the ignition or engine control switch “off”, remove
the thermostat cover (see Figure 5). Using an
ohmmeter, check the resistance between the metal
end cover and the heater post (see Figure 5). (Note:
On the dual terminal end cover, check the resistance
between the two terminals.) For a 12 volt, 60 watt
end cover, the resistance should be 2.0 - 2.8 ohms
and for a 24 volt, 120 watt end cover, 4.0 - 5.6 ohms.
These resistance values apply to either single or dual
terminal air dryer end covers. If the heater resistance
value obtained is outside the stated limits, a new or
remanufactured end cover should be installed, since
the heater element cannot be serviced. Check that
a good ground path exists between the air dryer end
cover casting and the vehicle chassis. Correct if
needed. If the heater resistance value obtained is
within the stated limits the thermostat should be
replaced (Kit Number 102657) or a new or
remanufactured end cover installed. Note: The dual
terminal air dryer cover requires kit number 103982.
D. Reassembly
Reinstall the thermostat cover as illustrated in Figure
5. Take special care to assure the rubber spacer
and the gasket are correctly installed, to assure
proper operation.
REBUILDING THE AD-4 ™ AIR DRYER
GENERAL
If, after completing the routine operation and leakage tests,
it has been determined that one or more components of the
air dryer requires replacement or maintenance, refer to the
following list to find the appropriate kit(s).
When rebuilding or replacing components of the air dryer
use only genuine Bendix parts. For ease in servicing the
AD-4
™ air dryer desiccant cartridge assembly, it is
recommended that the air dryer be removed from the vehicle.
MAINTENANCE KITS AVAILABLE:
103817 Major Maintenance Kit
This kit contains the parts necessary to completely
rebuild the AD-4
™ air dryer (desiccant cartridge
included) and includes kit 103980.
103818 AD-4 ™ Air Dryer Purge Valve Maintenance Kit
This kit contains the parts necessary to rebuild the
AD-4
™ air dryer end cover purge valve only.
103879 AD-4 ™ Air Dryer Seal Kit
This kit contains the outlet port check valve and the
o-rings and seals required when removing the end
cover assembly. This kit is included with kits 103980
and 103981.
103980 End Cover Maintenance Kit
This kit contains the parts necessary to rebuild the
end cover of the AD-4
™ air dryer and includes kit
103818.
103981 Desiccant Cartridge Replacement Kit
This kit contains the parts necessary to change
the desiccant cartridge only.
102657 Thermostat Maintenance Kit (single terminal
models)
This kit contains the parts necessary to rebuild a
single terminal thermostat assembly in the AD-4
™
air dryer.
103982 Thermostat Maintenance Kit (dual terminal
models)
This kit contains the parts necessary to rebuild a
two terminal thermostat assembly (insulated
ground).
288918 Thermostat Cover Replacement Kit (single
terminal models)
This kit contains the necessary components for
replacing the non-metallic thermostat cover.
104964 Thermostat Cover Replacement Kit (dual terminal
models)
This kit contains the necessary components for
replacing the non-metallic thermostat cover.
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO
AVOID
PERSONAL INJURY OR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove ignition key when
working under or around the vehicle. When
working in the engine compartment, the engine
should be shut off and the ignition key should be
removed. Where circumstances require that the
engine be in operation, EXTREME CAUTION should
be used to prevent personal injury resulting from
contact with moving, rotating, leaking, heated or
electrically charged components.