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  1. 1. ZJ REAR WINDOW DEFOGGER 8N - 1 REAR WINDOW DEFOGGER CONTENTS page pageDIAGNOSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 SERVICE PROCEDURES ................... 4GENERAL INFORMATION . . . . . . . . . . . . . . . . . . 1 GENERAL INFORMATION The electrically-heated rear window defogger is A repair kit is available to repair the grid lines andstandard equipment on Grand Cherokee models. Fol- bus bars, or to reinstall the heated glass pigtaillowing are general descriptions of the major compo- wires.nents in the rear window defogger system. Refer toGroup 8W - Wiring Diagrams for complete circuit de- DEFOGGER SWITCHscriptions and diagrams. The rear window defogger switch is mounted in the right instrument panel switch pod. The switch circuitREAR WINDOW GLASS GRID is protected by fuse 23 in the fuseblock module. Ac- The heated rear window glass has two electrically- tuating the switch energizes the relay and electronicconductive vertical bus bars and a series of horizon- timer. A light-emitting diode (LED) with an ambertal grid lines made of a silver-ceramic material, lens in the switch illuminates to indicate when thewhich is baked on and bonded to the inside surface of system is turned on. The defogger switch can not bethe glass. The grid lines and bus bars comprise a repaired. If faulty, the switch must be replaced.parallel electrical circuit. When the rear window defogger switch is placed in DEFOGGER RELAY/TIMERthe ON position, current is directed to the rear win- The defogger relay/timer is located in the relay cen-dow grid lines through the bus bars. The grid lines ter, which is under a cover in the glove box. Whenheat the rear window to clear the surface of fog orsnow. Circuit protection for the heated grid circuit is the rear defogger switch is actuated, the rear defog-provided by a circuit breaker in cavity 28 of the fuse- ger relay is energized. This causes current to flowblock module. through the grid circuit for approximately 10 min- The grid lines and bus bars are highly resistant to utes, or until the rear window defogger switch or ig-abrasion. However, it is possible for an open to occur nition switch are turned off. Power for the relay isin an individual grid line resulting in no current flow protected by fuse 19 in the fuseblock module. The de-through the line. The grid lines can be damaged or fogger relay/timer can not be repaired and, if faulty,scraped off with sharp instruments. Care should be must be replaced.taken in cleaning the glass or removing foreign ma-terials, decals or stickers. Normal glass cleaning sol-vents or hot water used with rags or toweling isrecommended. DIAGNOSISSYSTEM TESTS (3) Monitor vehicle voltmeter. With the control Electrically-heated rear window defogger operation switch ON, a distinct needle deflection should becan be confirmed in the following manner: noted. (1) Turn the ignition switch to the ON position. (4) The rear window defogger operation can be (2) Turn rear window defogger control switch ON. checked by feeling the glass. A distinct difference in
  2. 2. 8N - 2 REAR WINDOW DEFOGGER ZJtemperature between the grid lines and adjacent lead of voltmeter. With positive lead of voltmeter,clear glass can be detected within 3 to 4 minutes of contact feed side vertical bus bar (point B of Fig. 1).operation. The voltmeter should read 10-14 volts. (5) Using a DC voltmeter, contact terminal A (Fig. (3) With negative lead of voltmeter, contact a good1) (passenger side) with the negative lead, and termi- body ground point. The voltage reading should notnal B (driver side) with the positive lead. The volt- change. A different reading indicates a poor groundmeter should read 10-14 volts. connection. (4) Connect negative lead of voltmeter to point A on ground side bus bar and touch each grid line at mid-point with positive lead. A reading of approxi- mately 6 volts indicates a line is good. A reading of zero volts indicates a break in the grid line between mid-point C and point B. A reading of 10-14 volts in- dicates a break between mid-point C and point A. Move toward break and voltage will change as soon as break is crossed. DEFOGGER SWITCH (1) Remove defogger switch from instrument panel. Use a jumper wire to apply 12 volts to terminal 1 of switch (Fig. 2). Using another jumper wire connect terminal 3 of switch to ground. The indicator lamp Fig. 1 Rear Window Glass Grid Test should light. If OK, go to next step. If not OK, re- Steps 3, 4 or 5 above will confirm system operation. place switch.Indicator light illumination means that there is (2) Remove jumper wires and connect an ohmme-power available at the output of the switch, but does ter to terminals 2 and 3 of switch. Push the switchnot confirm that power is reaching the rear window button. Ohmmeter should read less than 1 ohm. Ifgrid lines. OK, go to next step. If not OK, replace switch. If the rear window defogger does not operate, the (3) Check defogger switch wiring circuits as fol-problem should be isolated in the following manner: lows: (1) Confirm that ignition switch is in ON position. • between switch connector cavity 1 and fuse 23 (2) Ensure that the heated rear window feed and • between switch connector cavity 3 and groundground wires are connected to the glass. Confirm • between switch connector cavity 2 and terminal 3that the ground wire has continuity to ground. of the relay. (3) Check fuses 19 and 23, and circuit breaker 28 Repair switch wiring shorts or opens as required.in the fuseblock module. Fuses and circuit breakermust be tight in their receptacles and all electrical DEFOGGER RELAYconnections must be secure. (1) Remove defogger relay from relay center and When the above steps have been completed and the turn ignition switch to ON position. Measure voltagesystem is still inoperative, one or more of the follow- at relay center cavity for defogger relay terminal 5.ing is faulty: Meter should show battery voltage. If OK, go to next• defogger switch step. If not OK, repair circuit to fuse 19 as required.• relay/timer (2) Measure voltage at relay center cavity for de-• rear window grid lines (all grid lines would have fogger relay terminal 4. The meter should read bat-to be broken or one of the feed wires disconnected for tery voltage. If OK, go to next step. If not OK, repairthe entire system to be inoperative). open from circuit breaker 28. If turning the switch ON produces severe voltmeter (3) Turn ignition switch to OFF position. Measuredeflection, check for a short circuit. resistance between relay center cavity for defogger relay terminal 1 and left (driver’s) side of defoggerREAR WINDOW GLASS GRID grid. The meter should read zero ohms. If OK, go to To detect breaks in grid lines, the following proce- next step. If not OK, repair circuit between relay anddure is required: defogger grid. (1) Turn ignition switch to the ON position. Turn (4) Measure resistance between relay center cavityrear defogger switch ON. The indicator lamp should for defogger relay terminal 2 and a good ground. Thelight. meter should read zero ohms. If OK, go to next step. (2) Using a 12-volt DC voltmeter, contact ground If OK, go to next step. If not OK, repair circuit be-side vertical bus bar (point A of Fig. 1) with negative tween relay center and ground.
  3. 3. ZJ REAR WINDOW DEFOGGER 8N - 3 (5) Install defogger relay in relay center. Turn ig- not OK, replace defogger relay.nition switch to ON position. Measure voltage at re-lay terminal 3. The meter should read near 5 volts. If Fig. 2 Defogger Switch Circuit REAR WINDOW DEFOGGER SYSTEM SCHEMATIC
  4. 4. 8N - 4 REAR WINDOW DEFOGGER ZJ SERVICE PROCEDURESREAR WINDOW GLASS GRID REPAIRS (7) Apply a thin layer of conductive epoxy to termi- The repair of grid lines, bus bars or pigtail wires nal or bare wire end of pigtail and place in desiredcan be accomplished using the MOPAR Rear Window location. To prevent terminal or pigtail from movingDefogger Repair Kit (P/N 4267922) or equivalent. while the epoxy is curing, it must be wedged or clamped.WARNING: MATERIALS CONTAINED IN REPAIR KIT (8) Carefully remove masking tape from grid line.MAY CAUSE SKIN OR EYE IRRITATION. CONTAINSEPOXY RESIN AND AMINE TYPE HARDENER, CAUTION: Do not allow the glass surface to exceedHARMFUL IF SWALLOWED. AVOID CONTACT WITH 400°F, glass may fracture.SKIN AND EYES. FOR SKIN, WASH AFFECTED AR-EAS WITH SOAP AND WATER. DO NOT TAKE IN- (9) Allow epoxy to cure 24 hours at room tempera-TERNALLY. IF TAKEN INTERNALLY, INDUCE ture or use heat gun with a 260°-371°C (500°-700°F)VOMITING; CALL A PHYSICIAN IMMEDIATELY. IF IN range for 15 minutes. Hold gun approximatelyCONTACT WITH EYES, FLUSH WITH PLENTY OF 254mm (10 inches) from repaired area.WATER. USE WITH ADEQUATE VENTILATION. DO (10) After conductive epoxy is properly cured re-NOT USE NEAR FIRE OR FLAME. CONTENTS CON- move wedge or clamp from terminal or pigtail andTAIN 3% FLAMMABLE SOLVENTS. KEEP OUT OF check operation of rear window defogger. Do not at-REACH OF CHILDREN. tach connectors until curing is complete. (1) Mask repair area so that the conductive epoxy DEFOGGER SWITCH REMOVE/INSTALLcan be applied neatly. Extend epoxy application onto (1) Disconnect battery negative cable.the grid line or the bus bar (Fig. 3) on either side of (2) Remove ash receiver.the break. (3) Remove 6 screws holding instrument panel cen- ter bezel (Fig. 4). Fig. 3 Grid Line Repair (Typical) (2) Follow instructions in repair kit for preparingdamaged area. (3) Remove package separator clamp and mix twoconductive epoxy components thoroughly withinpackaging. Fold package in half and cut center cor-ner to dispense epoxy. (4) For grid line, mask area to be repaired withmasking tape or a template (Fig. 3). (5) Apply epoxy through slit in masking tape ortemplate. Overlap both ends of the break by at least19mm (.75 in.). (6) For a terminal or pigtail replacement, mask ad-jacent areas so epoxy can be extended onto line aswell as bus bar. Apply a thin layer of epoxy to areawhere terminal or pigtail was fastened and onto ad- Fig. 4 Instrument Panel Center Bezeljacent grid line. (4) Remove center bezel.
  5. 5. ZJ REAR WINDOW DEFOGGER 8N - 5 (5) Remove 2 screws holding dash pad located be-hind top of center bezel. (6) Gently pry defroster grille out of dash pad. (7) Unplug auto head lamp and sun sensors (ifequipped) and set defroster grille aside. (8) Remove 4 screws in defroster duct openingholding dash pad (Fig. 5). Fig. 5 Upper Dash Pad Attaching Screws (9) Remove 3 screws above instrument panel clus-ter holding dash pad (Fig. 6). Fig. 7 Lower Instrument Panel Trim Fig. 6 Remove Screws Holding Dash Pad (10) Open glove box and remove 2 screws holdingdash pad. (11) Remove dash pad by pulling up to unsnap endclips. (12) With left front door open, remove 1 screw fromthe side of the lower instrument panel trim (Fig. 7). (13) Remove 4 screws holding the steering columncover (Fig. 8). (14) Remove 1 screw from bottom of lower instru-ment panel trim and pull panel off. There is also a Fig. 8 Steering Column Cover and Knee Blockerclip holding the panel to the instrument panel. (15) Remove 6 screws holding knee blocker. (16) Remove steering column retaining nuts.
  6. 6. 8N - 6 REAR WINDOW DEFOGGER ZJ(17) Remove 3 screws holding bottom of bezels (Fig.9). Fig. 9 Remove Screws Holding Bottom Of Bezels (18) Remove 2 screws holding top of end andswitch pod bezels (Fig. 10). The end bezel can now beremoved. Fig. 11 Left Switch Pod Bezel Screws Fig. 10 Remove Screws Holding Top of Bezels (19) Remove 2 screws holding left switch pod bezel(Fig. 11). (20) Remove 3 screws holding right switch pod be-zel (Fig. 12). Fig. 12 Right Switch Pod Bezel Screws
  7. 7. ZJ REAR WINDOW DEFOGGER 8N - 7(21) Pull switch pod bezel out far enough to removeswitch connectors. Disconnect connectors from eachswitch pod and remove bezel (Fig. 13). Fig. 14 Relay Center Cover Fig. 13 Rear View Of Switch Pod Bezel (22) Remove required switch pod attaching screwsand switch pod. (23) Reverse the removal procedures to install.Tighten steering column retaining nuts to 12 N⅐m(105 in. lbs.).DEFOGGER RELAY/TIMER REMOVE/INSTALL (1) Open glove box and remove 3 screws holdingrelay center cover (Fig. 14). (2) Remove the red relay from the relay center(Fig. 15). (3) Align relay terminals with cavities in relay cen- Fig. 15 Rear Window Defogger Relayter and push relay into place. (4) Re-install relay center cover.