Truck Troubleshooting Guide
Contents
1. MERITOR WABCO Truck Troubleshooting Guide SECONDARY CONTROL cl um mm mE EE EN P TO SERVICE A RELAY PRIMARY TANK INSET A OPTION PRIOR TO MARCH 1 1998 FMVSS 121 REGULATIONS INVERSION VALVE AND QUICK RELEASE VALVE INCLUDES ANTI COMPOUNDING 2 z4 SECONDARY x ES I g SUPY W z 9 WETTANK COLOR KEY 5 SUPPLY SECONDARY PRIMARY PARK EMERGENCY ABS ELECTRICAL ISSUED 10 99 TP 9974 Truck Troubleshooting Guide CONDITION REMEDY amp D COMPRESSOR i FOR TROUBLESHOOTING INFORMATION REFER TO THE QEM OPERATING INSTRUCTIONS NOTE If the compressor is manufactured by Meritor WABCO refer to Maintenance Manual 31 318 Compressor for Mack E Tech Engines or contact the Meritor Customer Support Center at 800 535 5560 2 SUPPLY PRIMARY AND SECONDARY AIR TANKS iM FOR TROUBLESHOOTING INFORMATION REFER TO THE OEM OPERATING INSTRUCTIONS o LOW PRESSURE INDICATOR SWITCH i BUZZER OR LIGHT INOPERABLE Check ground and wiring on switch and buzzer light Replace switch or buzzer light mg WON T OPERATE AT PRESSURES BELOW 60 P S I Check dash gauge for accuracy Replace switch or buzzer light O SAFETY VALVE mg POPS OFF EXCESSIVELY Check system pressure Valve operating properly when venting at 140 150 P S I as required Check unloader governor iM POPS OFF AT LESS THAN 140 P S I Replace B LEAKS Rep2. RSION VALVE IS NOT FUNCTIONING PROPERLY B LEAKS Repair or replace Q AIR DRYER BI AIR LEAKING CONSTANTLY FROM PURGE VALVE Purge valve seal damaged Replace Purge valve frozen Inspect heater see heater problems ll HEATER INOPERATIVE Blown Fuse Check fuse and replace with 8 10 amp fuse Broken wires or poor connections Repair or replace wiring to heater il SLOW WET TANK BUILD UP Filter and or desiccant plugged Service air dryer Ifa System Saver Series air dryer is installed refer to Meritor WABCO Maintenance Manual 34 Single Canister or 35 TWIN Printed in the USA CONDITION REMEDY ABS ELECTRONIC CONTROL UNIT MODULAR VALVES SENSORS AND TOOTH RINGS iM FOR TROUBLESHOOTING INFORMATION REFER TO THE QEM OPERATING INSTRUCTIONS 20 FRONT AXLE VALVE PACKAGE OPTIONAL i COMBINES TWO MODULATOR VALVES AND QUICK RELEASE VALVE aD REAR AXLE VALVE PACKAGE OPTIONAL i COMBINES TWO MODULATOR VALVES AND RELAY VALVE NOTE If the vehicle has Meritor WABCO ABS refer to Meritor WABCO Maintenance Manual 28 C version ABS or 30 D version ABS Information contained in this publication was in effect at the time the publication was approved for printing and is subjectto change without notice or liability Meritor WABCO reserves the right to revise the information presented or discontinue the production of parts described at any time TP 9974 Issued 10 99 16579 24240
3. TEM FOOT BRAKE VALVE mW LEAKS AT EXHAUST WITH ALL BRAKES RELEASED Check anti compound double check valve 16 Check 718A amp 18B for back flow into service control line Check seal in spring brake for back flow of spring hold off pressure through service port to open exhaust on valve Replace 15 Spring Parking Brake iE CAUTION CHOCK WHEELS REPAIR AND REPLACE ITEMS AS NECESSARY lii LEAKS AT EXHAUST WITH FOOT BRAKE APPLIED Foot valve defective Repair or replace il LEAKS AT EXHAUST WITH ALL PARK BRAKES SET IN PARK POSITION AND FOOT BRAKE RELEASED Foot valve defective Repair or replace Q QUICK RELEASE VALVE lii LEAKS AT EXHAUST PORT WITH ALL BRAKES RELEASED Check and replace 718A or 18B if back flow occurs into secondary control line ii LEAKS WHEN SERVICE BRAKES ARE APPLIED Repair or replace SERVICE BRAKE CHAMBER iM FOR TROUBLESHOOTING INFORMATION REFER TO THE QOEM OPERATING INSTRUCTIONS SLACK ADJUSTER il FOR TROUBLESHOOTING INFORMATION REFER TO THE QEM OPERATING INSTRUCTIONS NOTE If the slack adjusters are manufactured by Meritor refer to Maintenance Manual 4B Automatic Slack Adjusters or contact the Meritor Customer Support Center at 800 535 5560 llamasin costo desde Mexico 001 800 889 1834 Qo RELAY VALVE lii LEAKS AT EXHAUST PORT WITH ALL BRAKES RELEASED Check seal in spring brake for back flow of spring hold off pressure through service port to open exhaust on v
4. alve Replace 15 Spring Parking Brake Check reservoir port for evidence of contamination check supply lines for rusty fittings or carbon deposits Repair or replace il LEAKS AT EXHAUST PORT WITH SERVICE BRAKES APPLIED Exhaust valve not seating properly Repair or replace Meritor WABCO Vehicle Control Systems 2135 West Maple Road Troy MI 48084 USA Copyright 1999 800 535 5560 Meritor WABCO www meritorauto com All Rights Reserved CONDITION REMEDY Qo SPRING PARKING BRAKE SERVICE ONLY SERVICE CHAMBER SIDE OF SPRING BRAKE iM FOR TROUBLESHOOTING INFORMATION REFER TO THE QOEM OPERATING INSTRUCTIONS O QUICK RELEASE AND DOUBLE CHECK VALVE COMBINATION iE FOOT VALVE EXHAUST LEAK PARK BRAKES RELEASED YELLOW DASH CONTROL V VALVE EXHAUST LEAK IN PARK POSITION AND SERVICE BRAKES APPLIED Check anti compound double check valve portion for feedback to foot or dash control valve Repair or replace Q STOP LIGHT SWITCH B LEAKS Replace Bl FAILS TO SIGNAL A GOOD BULB THROUGH SOUND WIRING AT 3 6 P S I Replace Q INVERSION RELAY VALVE WITH THE LOSS OF REAR SERVICE BRAKES 13 APPLICATION OF SPRING BRAKE BY USING THE EMERGENCY SECTION SHOULD BE AVAILABLE ALONG WITH FRONT SERVICE BRAKE BY APPLYING FOOT VALVE il PERIODICALLY TEST BY BLEEDING PRIMARY SERVICE TANK AND OBSERVING FRONT BRAKE AND REAR SPRING BRAKE APPLICATION UPON DEPRESSING FOOT PEDAL REPAIR OR REPLACE IF AFTER CHECKING INVE
5. lace BB WON T FUNCTION Periodic Test remove and test above 150 P S I with shop air Replace if non functional DRAIN VALVES MANUAL B LEAKS Replace DRAIN VALVES AUTOMATIC mg WON T DRAIN Repair or replace mg WON T DRAIN IN COLD WEATHER Replace with heated unit Bi LEAKS MALFUNCTIONS Repair or replace Periodic Test with system pressure stabilized compressor unloaded no leak evident at discharge port make several foot brake applications to reduce wet tank pressure Moisture should drain from discharge port GOVERNOR B FLUTTERS Check gauge Check unloader line size 5 16 x 5 maximum Check air actuated accessory Is the air volume requirement greater than governor capacity Check for plugged governor reservoir line Repair adjust or replace governor WON T PASS AIR TO UNLOADER TO CUT OUT COMPRESSOR Check governor reservoir line Repair or replace MERITOR WABCO CONDITION REMEDY eb SINGLE CHECK VALVE il ALLOW BLEED BACK TO SUPPLY RESERVOIR Periodic Test bleed supply reservoir and observe gauges Check valves should maintain primary and secondary reservoir pressure Replace if test results are negative PRESSURE CONTROL CHECK VALVE i WILL NOT PERMIT AIR TO PURGE AIR DRYER CHECK THAT ONE WAY CHECK HAS BEEN REMOVED AIR GAUGE iM FOR TROUBLESHOOTING INFORMATION REFER TO THE QOEM OPERATING INSTRUCTIONS Q DUAL SYS
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