Operational and Leakage Tests
- 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 for a single vehicle; or 3 psi/minute for a tractor trailer, inspect the vehicle air systems for sources of leakage, and repair them. Refer to troubleshooting information in Bendix 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 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 service literature.
- Check operation of the end cover heater and thermostat
assembly during cold weather, as follows:
- Electric Power to the Dryer: With the ignition or engine kill switch 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 resistance between the electrical
pins in the air dryer connector half. 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. Resistance should exceed 1000 ohms. If resistance values obtained are within stated limits, the thermostat and heater assembly is operating properly. If resistance values obtained are outside stated limits, replace the heater and thermostat assembly.
- On the AD-IS/dryer reservoir module (DRM) only, observe
the pressure gauges of the vehicle as system pressure builds from
zero. The primary gauge should rise until it reaches approximately
109±5 psi (751±34 kPa), then level off (or a momentary
slight fall) as the second pressure protection valve opens supplying
the secondary reservoir. When the secondary pressure gauge passes
through approximately 55±5 psi (379±34 kPa) and then
85±5 psi (586±34 kPa) there should be an associated
levelling off (or momentary slight fall) of pressure as the third
and fourth pressure protection valves open. Finally, both the primary
and secondary gauges should reach their full pressure of approximately
130±5 psi (896±34 kPa). If the AD-IS does not perform
within the pressure ranges described above, recheck using gauges known
to be accurate. If readings remain outside the ranges outlined above,
replace the AD-IS.
There are no kits available for servicing the pressure protection valves.
Warning: Do not attempt to adjust or service the pressure protection valves. Incorrect pressure protection valve settings can result in automatic application of the vehicle spring brakes without prior warning. This can cause personal injury or property damage.