BENDIX AD-2 AIR DRYER Manual - Página 5

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A. An outside air source has been used to charge the

system. This air did not pass through the drying

bed.

B. Air usage is exceptionally high and not normal for a

highway vehicle. This may be due to accessory air

demands or some unusual air requirement that does

not allow the compressor to load and unload

(compressing and non-compressing cycle) in a

normal fashion. Check for high air system leakage.

C. The air dryer has been installed in a system that

has been previously used without an air dryer. This

type system will be saturated with moisture and

several weeks of operation may be required to dry it

out.

D. Location of the air dryer is too close to the air

compressor. Refer to "Installation" section.

E. In areas where more than a 30° range of temperature

occurs in one day, small amounts of water can

accumulate in the air brake system due to

condensation. Under these conditions, the presence

of small amounts of moisture is normal and should

not be considered as an indication that the dryer is

not performing properly.

Note also that a small amount of oil in the system

may be normal and should not, in itself, be considered

a reason to replace the desiccant; oil stained

desiccant can often function adequately.

2. Check mounting bolts for tightness.

3. Check the operation of the integral single check valve

in the AD-2

™

air dryer or the "in line" check valve used

with the AD-1

™

air dryer. Build the air system to governor

cut-out and observe the test air gauge installed in the

#1 reservoir. A rapid loss of pressure could indicate a

failed check valve. This can be confirmed by checking

at the purge valve exhaust. (Note: Purge valve will be

FIGURE 5

open when governor cut-out pressure is reached. Allow

two minutes for purge cycle before testing the check

valve.)

4. Check for excessive leakage at the purge valve by

coating the exhaust with a soap solution while the

compressor is loaded. (compressing air)

5. Check the operation of the safety valve by pulling the

exposed stem while the compressor is loaded.

(compressing air) There must be an exhaust of air while

the stem is held and the valve should reseat when the

stem is released.

6. Check all lines and fittings leading to and from the air

dryer for leakage and integrity.

7. Check the operation of the end cover heater and

thermostat assembly during cold weather operation as

follows:

A. Electric Power to the Dryer

With the ignition or engine control "on", check for

power at the dryer's electrical terminal (see Figure

16) with a voltmeter or test light. If there is no voltage,

look for a blown fuse, broken wires, or corrosion in

the vehicle wiring harness.

B. Thermostat and Heater

1. Turn off the ignition switch and cool the end cover

assembly to below 40°F . With an ohmmeter check

the resistance between the electrical terminal and

the aluminum of the end cover (see Figure 16).

This resistance should be 2.0 - 4.0 ohms for a

12 volt end cover, 8.1 -13 ohms for a 24 volt, 60

watt cover, and 4.0 - 7.0 ohms for a 24 volt, 120

watt end cover.

2. Warm the end cover assembly to over 90°F . and

check the resistance as above. This resistance

should exceed 1,000 ohms.

If these resistances are within the limits, the

thermostat and heater are operating properly.

If these resistances are outside the limits,

proceed to Step C to determine the cause.

C. Heater Element

With the ignition or engine control switch "off",

remove the thermostat cover (see Figure 17). With

an ohmmeter check the resistance between the

aluminum of the end cover and the heater post (see

Figure 17). For a 12 volt end cover, the resistance

should be 2.0 - 2.8 ohms. For a 24 volt, 60 watt end

cover, 8.1 - 11.1 ohms, and for a 24 volt, 120 watt

end cover, 4.0 - 4.6 ohms. If the heater resistance

is outside these ranges, a new or remanufactured

end cover should be installed, since the heater

element cannot be serviced.

If the heater resistance is within the limits the

thermostat should be replaced (Kit Number 102637)

or a new or remanufactured end cover installed.