Bendix AD-9 Repair Kits
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Extended Maintenance Intervals
Bendix AD-9 air dryers have a large capacity desiccant cartridge that allows for longer maintenance intervals. Air dryer rebuilds can be stretched to every 36 months when the AD-9 is installed on a typical over-the-road truck or tractor.
Easy To Service
Desiccant cartridge replacement is the only reason to ever completely disassemble the Bendix AD-9 air dryer. The check valve, turbo cut-off valve, heater, and purge valve assembly can all be serviced without disassembling the air dryer.
Troubleshooting the Bendix AD-9 Air Dryer
This troubleshooting documentation was compiled from Bendix's AD-9 Service Data Sheet. Download the data sheet for more detailed information.
- Dryer is constantly "cycling" or purging. Dryer purges frequently (every 4 minutes or less while vehicle is idling)
- Excessive system leakage IMPORTANT: Note whether air pressure loss is shown on dash gauge(s). Pressure loss shown on gauges is caused by service brake system or component leakage. Pressure loss NOT SHOWN on gauges is caused by supply system or component leakage.
- Leaking purge valve housing assembly and/or O-rings in air dryer end cover.
- Holset® "E" type compressor - When installing a Bendix Drop-In air dryer in a system equipped with a Holset E or QE compressor, remove the Holset ECON valve along with its feedback and governor control line.
- Water and/or Oil in Supply or Service Reservoir
- Desiccant cartridge needs to be replaced
- Improper discharge line length or line material - Maximum air dryer inlet temperature is exceeded.
- Air system charged from outside air source (outside air not passing through air dryer)
- Air dryer not purging
- Purge (air exhaust) time insufficient due to excessive system leakage
- Excessive air usage, duty cycle too high
- Compressor malfunction - Passing oil
- Air bypasses desiccant cartridge assembly - If vehicle has a Holset compressor, inspect feedback check valve.
- Oil present at air dryer purge exhaust or cartridge during maintenance
- A small amount of oil in these areas is normal.
- Safety valve on air dryer "popping off" or exhausting air
- Restriction between air dryer and supply reservoir
- Air dryer safety valve malfunction
- Desiccant cartridge needs to be replaced
- Governor malfunction. Missing or restricted governor control line installation
- Constant exhaust of air at air dryer purge valve exhaust when air dryer is in Charge mode.
- Air dryer purge valve leaking excessively
- Compressor fails to unload (stop compressing air) and air dryer purge exhaust makes "sputtering" or "popping" sound
- Purge control line connected to reservoir or exhaust port of governor. It must be connected to an unloader port on the governor.
- Purge valve frozen open - malfunctioning heater and thermostat, wiring, blown fuse.
- Excessive system leakage
- Purge valve stays open - supply air leaks to control side - Replace purge valve and housing
- Can not build system air pressure
- Inlet and outlet air connections reversed
- Check valve between air dryer and first reservoir malfunctioning
- Kinked or blocked discharge line
- Excessive bends in air compressor discharge line causing water to collect and freeze
- Governor malfunction
- Air dryer does not purge or exhaust air
- Missing, broken, kinked, frozen, plugged or disconnected purge control line
- Faulty air dryer purge valve
- Air dryer safety valve malfunction
- Desiccant material being expelled from air dryer purge valve exhaust
- Air dryer not securely mounted. (Excessive vibration.)
- Malfunctioning or saturated desiccant cartridge
- Compressor passing excessive amount of oil
- Desiccant cartridge not assembled properly to end cover. (Loose attachment)
- "Pinging" noise excessive during compressor loaded cycle
- Defective check valve assembly in air dryer end cover.
- Leaking purge valve control piston o-ring.
- Constant leaking of air at air dryer purge valve exhaust (non-charging mode.)
- Defective check valve assembly in air dryer end cover.
- Leaking purge valve control piston o-ring.
- The air dryer purge piston cycles rapidly in the compressor unloaded (non-compressing) mode.
- Compressor fails to "unload"
