SD-08-2407 ® Bendix® AD-4™ Air Dryer UPPER BRACKET UPPER BRACKET LOWER BRACKET LOWER BRACKET SUPPLY PORT CONTROL PORT SUPPLY PORT THERMOSTAT TERMINAL PURGE EXHAUST EXTENDED PURGE AD-4™ AIR DRYER DELIVERY PORT PURGE EXHAUST STANDARD AD-4™ AIR DRYER FIGURE 1 - AD-4™ AIR DRYER MODELS DESCRIPTION The function of the AD-4™ air dryer is to collect and remove air system contaminants in solid, liquid and vapor form before they enter the brake system.
CHECK VALVE ORIFICE PURGE VOLUME DESICCANT CARTRIDGE DESICCANT BED OIL SEPARATOR CHECK VALVE DELIVERY PORT HEATER EXHAUST PORT CONTROL GOVERNOR PURGE VALVE COMPRESSOR SUPPLY RESERVOIR FIGURE 2 - AD-4™ AIR DRYER CHARGE CYCLE OPERATION OF THE AD-4™ AIR DRYER The AD-4™ air dryer alternates between two operational modes or “cycles” during operation: the charge cycle and the purge cycle. The following description of operation is separated into these “cycles” of operation.
CHECK VALVE ORIFICE PURGE VOLUME DESICCANT CARTRIDGE DESICCANT BED OIL SEPARATOR CHECK VALVE DELIVERY PORT EXHAUST PORT CONTROL GOVERNOR HEATER PURGE VALVE COMPRESSOR SUPPLY RESERVOIR FIGURE 3 - AD-4™ AIR DRYER PURGE CYCLE line connecting the governor unloader port to the AD-4™ air dryer end cover control port is pressurized when the governor unloads the compressor. Air pressure at the AD-4™ air dryer end cover control port is also present on the purge valve piston.
CHECK VALVE PURGE ORIFICE PURGE VOLUME DESICCANT CARTRIDGE DESICCANT BED CHECK VALVE ASSEMBLY PERFORATED PLATE OIL SEPARATOR NUT SEALING RING WASHER SEALING RING SEALING RING SEALING RING END COVER SPECIAL WASHER HEX HEAD SCREW SPRING DELIVERY PORT PURGE VALVE EXHAUST DIAPHRAGM PURGE PISTON EXHAUST COVER SUPPLY PORT O-RING FIGURE 4 - AD-4™ AIR DRYER SECTIONAL VIEW Every 900 operating hours or 25,000 miles or every three (3) months: 1.
2. Check mounting bolts for tightness. Retorque to 270385 inch pounds. 3. Perform the Operation & Leakage Tests listed in this publication. 6. 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 kill switch in the ON position, check for power at the dryer’s electrical terminal using a voltmeter or test light.
resistance should be 2.0 to 4.0 ohms for the 12 volt, 60 watt end cover and 4.0 - 7.0 ohms for the 24 volt, 120 watt end cover. These resistance values apply to either single or dual terminal air dryer end covers. Warm the end cover assembly to over 90 degrees Fahrenheit and again check the resistance as above. The resistance should exceed 1000 ohms for both single and dual terminal air dryers.
MOUNTING STRAP LOCKWASHER CAP SCREW 5/16” X 4-1/2” NUT SEALING RING BRACKET MOUNTING STRAP LOCKWASHER CAP SCREW 5/16” X 4-1/2” BRACKET SEALING PLATE NUT MOUNTING BRACKET HOOK (4) DESICCANT CARTRIDGE CAP SCREW & LOCKWASHER (8) LOCK NUT (8) SPECIAL WASHER SEALING RING AIR DRYER HOUSING SEALING RING PURGE PISTON O-RING SPRING CONTROL PORT CHECK VALVE ASSEMBLY SUPPLY PORT DELIVERY PORT END COVER HEATER VOLTAGE SHOWN SPECIAL WASHER (8) CAP SCREW 3/8” SAFETY VALVE DESICCANT CARTRIDGE PURGE V
3. Do not attempt to install, remove, disassemble or assemble a component until you have read and thoroughly understand the recommended procedures. Use only the proper tools and observe all precautions pertaining to use of those tools. 4. If the work is being performed on the vehicle’s air brake system, or any auxiliary pressurized air systems, make certain to drain the air pressure from all reservoirs before beginning ANY work on the vehicle.
the end cover. Remove and discard the three sealing rings. One sealing ring is located in the groove on the sealing plate and the other two are in grooves in the end cover. 2. Remove 1/4" cap screw from the bottom of the purge valve and remove the diaphragm washer, exhaust diaphragm and purge valve. Discard the exhaust diaphragm and purge valve. Remove purge piston. Note: Hold piston down when removing cap screw due to spring tension. 3.
3/8" bolts require replacement, insure that the replacement bolts are grade 5 minimum and the same length as the original bolts. Use of inferior bolts can compromise the integrity of the air dryer and lead to premature failure. Where a lower, right angle mounting bracket (instead of a lower mounting strap) is used; line up the marks made on the outer housing and end cover. Install the six (standard) 3/8" cap screws, lock nuts and twelve special washers.
RE-INSTALLATION 1. Install the assembled AD-4™ air dryer (if an AD-4™ air dryer with a lower right angle bracket instead of a lower mounting strap is being serviced proceed to step #2) on the vehicle by sliding it into mounting brackets until mounting bracket hook catches under the lip of the cover. Proceed to step #3. 2. Install the assembled AD-4™ air dryer back onto the vehicle by slipping it into the upper mounting bracket.
VEHICLE PREPARATION 1. Park the vehicle on a level surface and prevent movement by means other than the brakes. 2. Drain all reservoirs to 0 p.s.i. (0 kPa). LOCATING AD-4™ AIR DRYER ON VEHICLE 1. The AD-4™ air dryer must be mounted vertically (purge exhaust toward road surface) outside the engine compartment in an area of air flow while the vehicle is in motion. The AD-4™ air dryer must not be exposed to direct wheel splash (located behind axle mud flap is acceptable). 2.
3. For AD-4™ air dryer end covers with a dual terminal (See Figure 6) heater connections, the power and insulated return wires may be connected to either terminal. An 8-10 amp fuse should be installed in the power carrying wire. Use 16 gauge wire for both power and return. 4. All electrical connections must be waterproofed. 5. Tie wrap or support all electrical wire leading to the AD-4™ air dryer at 6 - 8 inch intervals. Note: Wires should have sufficient slack and not be completely taught.
AD-4™ AIR DRYER TROUBLESHOOTING CHART SYMPTOMS 1. Dryer is constantly “cycling” or purging. Dryer purges frequently (every 4 minutes or less while vehicle is idling). CAUSE A. 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. REMEDY A.
AD-4™ AIR DRYER TROUBLESHOOTING CHART (Continued) SYMPTOMS CAUSE REMEDY 1. Test fittings, hoses, lines and connections. Apply soap solution to detect excessive leakage. Tighten or replace as needed then repeat the air dryer charge-purge cycle and observe the gauge installed in the supply reservoir. If leakage is within limits remove gauge from reservoir and replace drain cock or valve. If excessive leakage is detected, continue testing. 2. Test accessories connected to supply reservoir.
AD-4™ AIR DRYER TROUBLESHOOTING CHART (Continued) SYMPTOMS CAUSE REMEDY 6. With gauge installed at RES port of governor, pressure should not drop below ”Cut-In” pressure at the onset of the compressor “Unloaded” cycle. If pressure drops, check for “kinks” or restrictions in line connected to RES port. Line connected to RES port on governor must be same diameter, or preferably larger than, lines connected to UNL port(s) on governor. B. Leaking purge valve in air dryer end cover (control side). B.
AD-4™ AIR DRYER TROUBLESHOOTING CHART (Continued) SYMPTOMS 2. Water and/or Oil in Supply or Service Reservoir (continued). CAUSE REMEDY C. Air dryer not purging (see Symptom #5). C. See Symptom #5. D. Purge (air exhaust) time insufficient due to excessive system leakage (see causes for Symptom #1). D. Check causes and remedies for Symptom #1. E. Excessive air usage, duty cycle too high - Air dryer not compatible with vehicle air system requirement (Improper air dryer/vehicle application). E.
AD-4™ AIR DRYER TROUBLESHOOTING CHART (Continued) SYMPTOMS 2. Water and/or Oil in Supply or Service Reservoir (continued). CAUSE F. Air compressor discharge and/or air dryer inlet temperature too high. REMEDY F. Restricted discharge line. See Appendix A, Table A, column 1 & 2 for recommended sizes. If discharge line is restricted or more than 1/16" carbon build up is found, replace the discharge line. Replace as necessary.
AD-4™ AIR DRYER TROUBLESHOOTING CHART (Continued) CAUSE REMEDY H. Air by-passes desiccant cartridge assembly. H. If vehicle uses Holset compressor, inspect feedback check valve for proper installation and operation. SYMPTOMS When replacing the desiccant cartridge, make sure desiccant cartridge assembly is properly installed and sealing rings are in place on mounting surface of desiccant cartridge. I. Desiccant requires replacement. I. Replace desiccant cartridge assembly.
AD-4™ AIR DRYER TROUBLESHOOTING CHART (Continued) SYMPTOMS 5. Constant exhaust of air at air dryer purge valve exhaust. (Charge mode.) 6. Can not build system air pressure. 7. Air dryer does not purge or exhaust air. 20 CAUSE REMEDY 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. A. Air dryer purge valve leaking excessively. A.
AD-4™ AIR DRYER TROUBLESHOOTING CHART (Continued) SYMPTOMS CAUSE REMEDY 8. Desiccant material being expelled from air dryer purge valve exhaust (may look like whitish liquid or paste or small beads.) 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.
Appendix A Table A: Maintenance Schedule and Usage Guidelines Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging system. Column 1 Vehicle Used for: Typical Compressors No. of Spec'd Axles Column 2 Discharge Line I.D. Length 1/2 in. 6 ft.
Appendix B Additional Troubleshooting Information The troubleshooting procedure presented on the following pages has been excerpted from a laminated card entitled: Troubleshooting Charging and Air Supply Systems. The complete card can be obtained from authorized Bendix parts outlets under literature number BW1779. It is presented here because of the air dryers connection to the supply air system and for convenience.
BW1450 © 2004 Bendix Commercial Vehicle Systems LLC All rights reserved. 10/2004 Printed in U.S.A.
