Bendix air dryer troubleshooting

Oil present at air dryer purge exhaust or cartridge during maintenance.A. Air brake charging system is functioning normally.A. Air dryers remove water and oil from the air brake charging system. A small amount of oil is normal. Check that regular maintenance is being performed and that the amount of oil in the air tanks (reservoirs) is within the acceptable range shown on the BASIC cup (see also column 5 of Appendix A, Table A.) Replace the air dryer cartridge as needed and return the vehicle to service.
4. Safety valve on air dryer “popping off or exhausting air.A. Restriction between air dryer and supply (first) reservoir.A. Check to determine if air is reaching supply reservoir. Inspect for kinked tubing or hose. Check for undrilled or restricted hose or tubing fittings and repair or replace as needed.
B. Air dryer safety valve malfunction.B. Verify relief pressure is at vehicle or component manufacturer specifications. Replace if malfunctioning.
C. Desiccant cartridge maintenance required.C. Refer to Appendix A Table A and column 3. Check compressor for excessive oil passing and/or correct compressor installation. Repair or replace as necessary. Replace desiccant cartridge.
D. Malfunctioning defective discharge check valve in end cover of the AD-9’* air dryer.D. Test to determine if air is passing through check valve. Repair or replace.
E. Excessive pressure pulsations from compressor. (Typical single cylinder type).E. Increase volume in discharge line by increasing length or diameter. Add a ping tank (small reservoir).
F. Governor malfunction. Missing or restricted governor control line installation.F. Test governor operation and/or inspect the control line leading from the governor UNL (unloader) port to the air dryer control port.
Constant exhaust of air at air dryer purge valve exhaust. (Charge mode.)A. Air dryer purge valve leaking excessively.A. With compressor loaded, apply soap solution on purge valve exhaust, to test for excessive leakage. Repair purge valve as necessary.
B. Compressor fails to unload (stop compressing air) and air dryer purge exhaust makes 'sputtering" or “popping" sound.B. Confirm failure to unload by increasing & decreasing engine RPM and noting change in the rate of leakage and intensity of accompanying leakage sound. Repair/replace compressor unloaders.
C. Purge control line connected to reservoir or exhaust port of governor.C. Purge control line must be connected to unloader port of governor.
D. Purge valve frozen open - malfunctioning heater and thermostat, wiring, blown fuse.D. Test heater and thermostat as described in Preventative Maintenance Section.
E. Excessive system leakage.E. See Symptom #1.
F. Purge valve stays open - supply air leaks to control side.F. Repair purge valve and housing.
Can not build system air pressure.A. Inlet and outlet air connections reversed.A. Connect compressor discharge to air dryer supply port. Reconnect lines properly.
B. Check valve between air dryer and first reservoir.B. Test check valve for proper operation. Repair or replace as necessary.
C. Kinked or blocked (plugged) discharge line.C. Check to determine if air passes through discharge line. Check for kinks, bends, excessive carbon deposits, or ice blockage.
D. Excessive bends in discharge line (water collects and freezes).D. Discharge line should be constantly sloping from compressor to air dryer with as few bends as possible.
E. Refer to Symptom 4. Causes E & F.E. Refer to Symptom #4. Remedies E & F.
Air dryer does not purge or exhaust air.A. Missing, broken, kinked, frozen, plugged or disconnected purge control line.A. Inspect control line from governor UNL (unloader) port to control port of air dryer. Test to determine air flows through purge control line when compressor unloaded. Check for undrilled fittings. (See Symptom #4. Remedy C.)
B. Faulty air dryer purge valve.B. After determining air reaches purge valve (Remedy A above), repair purge valve.
C. See Causes B, E. G for Symptom #4.C. See Causes. B. E, G for Symptom #4.
Desiccant material being expelled from air dryer purge valve exhaust (may look like whitish liquid or paste or small beads.) -OR- Unsatisfactory desiccant life.A. This symptom is almost always accompanied by one or more of Symptoms 1, 2, 3.4 and 5. See related causes for these Symptoms above.A. See Causes and Remedies for Symptoms 1,2, 3, 4 and 5.
B. Air dryer not securely mounted. (Excessive vibration.)B. Vibration should be held to minimum. Add bracket supports or change air dryer mounting location if necessary.
C. Malfunctioning or saturated desiccant cartridge.C. Replace desiccant cartridge assembly.
D. Compressor passing excessive oil.D. Check for proper compressor installation; if symptoms persist, replace compressor.
E. Desiccant cartridge not assembled properly to end cover. (Loose attachment)E. Check the torque on the desiccant cartridge to end cover attachment. Refer to assembly section of this service data sheet.
“Pinging" noise excessive during compressor loaded cycle.A. Defective check valve assembly in AD-9" air dryer end cover.A. Refer to Remedy C. Symptom #1.
B. Leaking Turbo Cutoff valve.B. Repair or replace purge valve assembly.
C. Leaking purge valve control piston o-ring.C. Repair or replace purge valve assembly.
Constant seepage of air at air dryer purge valve exhaust (non-charging mode.)A. Defective check valve assembly in AD-9" air dryer end cover.A. Refer to Remedy C. Symptom #1.
B. Leaking Turbo Cutoff valve.B. Repair or replace purge valve assembly.
C. Leaking purge valve control piston o-ring.C. Repair or replace purge valve assembly.
The air dryer purge piston cycles rapidly in the compressor unloaded (non- compressing) mode.A. Compressor fails to “unload”.A. Faulty governor installation; no air line from governor to compressor or line is kinked or restricted. Install or repair air line.