LOUD KNOCK FROM A/C COMPRESSOR

SUBJECT: LOUD KNOCK FROM A/C COMPRESSOR (REPLACE COMPRESSOR AND THERMAL EXPANSION VALVE)

MODELS: 1994-95 CHEVROLET AND GMC C/K MODELS WITH REAR A/C (RPO C69) OR REAR HEATER AND A/C (RPOS C36,C69) BUILT BEFORE THE FOLLOWING VIN BREAKPOINTS:

DIVISION VIN CHEVROLET SJ300349 GMC TRUCK SJ701253

CONDITION:

SOME OWNER'S OF THE ABOVE LISTED VEHICLES MAY COMMENT THAT THE A/C COMPRESSOR HAS DEVELOPED A LOUD KNOCKING NOISE. THE A/C SYSTEM WILL CONTINUE TO COOL.

CAUSE:

WHEN THE REAR A/C SYSTEM IS SHUT OFF, A REFRIGERANT FLOOD BACK CONDITION MAY OCCUR THROUGH THE REAR A/C SYSTEM. THIS FLOODING DEGREASES THE INTERNAL PARTS OF THE COMPRESSOR RESULTING IN RAPID SLIDER BLOCK WEAR AND THE RESULTING LOUD KNOCKING NOISE. A POOR CONTACT BETWEEN THE TXV CAPILLARY TUBE AND THE REAR EVAPORATOR OUTLET TUBE CAN ALLOW THE TXV TO REMAIN OPEN WHEN THE REAR SYSTEM IS NOT IN USE. THE OPEN TXV MAY ALLOW LIQUID REFRIGERANT TO FLOOD BACK THROUGH THE REAR SYSTEM (LIQUID LINE, TXV, EVAPORATOR, REAR SUCTION LINE) AND SUBSEQUENTLY FLOOD THE COMPRESSOR.

CORRECTION:

REPLACE THE A/C COMPRESSOR, THE THERMAL EXPANSION VALVE (TXV), AND ADD AN IN-LINE FILTER.

SERVICE PROCEDURE

1. RECOVER THE R-134A REFRIGERANT CHARGE (SECTION 1-B OF SERVICE MANUAL). 2. REPLACE THE COMPRESSOR AND BALANCE THE PAG LUBRICANT IN THE SYSTEM FOLLOWING THE PROCEDURES IN THE VEHICLE SERVICE MANUAL. 3. INSTALL AN IN-LINE FILTER IN THE LIQUID LINE AFTER THE CONDENSER AND BEFORE THE "Y" IN THE LINE SEPARATING THE FRONT AND REAR SYSTEMS. 4. REMOVE, INSPECT AND CLEAN THE ORIFICE TUBE FOR THE FRONT SYSTEM. IT IS LOCATED IN THE LIQUID LINE AFTER THE "Y" JOINT. 5. REPLACE THE ORIFICE TUBE. 6. DISCONNECT SEAT BELT AND REMOVE REAR BENCH SEAT. 7. REMOVE THE RIGHT SECOND PASSENGER SEAT SHOULDER BELT RETAINER FROM THE RIGHT SIDE C-PILLAR. 8. REMOVE THE (5) SCREWS FROM THE RIGHT SIDE C-PILLAR TRIM. 9. REMOVE THE (2) SCREWS SECURING THE RIGHT SIDE LOWER TRIM PANEL TO THE C-PILLAR. 10. REMOVE THE (5) SCREWS SECURING THE D-PILLAR COVERS. 11. LIFT THE RIGHT SIDE LOWER TRIM PANEL AND ROLL FORWARD TO REMOVE, THIS EXPOSES THE REAR HVAC EVAPORATOR CASE MODULE. 12. USING TEMPLATE (FIG. 4), MARK CUTTING LINES ON THE UPPER EVAPORATOR CASE USING A CHINA MARKER OR EQUIVALENT. DO NOT REMOVE THE LOCATING TABS FROM THE TEMPLATES, THEY ARE NEEDED TO POSITION THE CUT AREA FOR THE ACCESS DOORS. (FIG. 1). 13. USING TEMPLATE (FIG. 5), MARK CUTTING LINES ON THE LOWER EVAPORATOR CASE USING A CHINA MARKER OR EQUIVALENT. (FIG. 1). 14. CUT THROUGH THE PLASTIC UPPER EVAPORATOR CASE AND THE LOWER EVAPORATOR CASE FOLLOWING THE MARKED OUTLINES OF THE TEMPLATES TO CREATE TWO ACCESS DOORS (FIG. 1). DO NOT CUT REAR EDGE OF EITHER ACCESS DOOR (FIG. 4 AND 5). USE A HOT KNIFE OR A SMALL (1/2" DIA.) ROTARY ABRASIVE CUTTING WHEEL.

NOTICE: CUT THROUGH PLASTIC CASE MATERIAL ONLY. ALUMINUM TUBES ARE LOCATED APPROXIMATELY 1/8" BEHIND THE CASE WALL (FIG. 2, VIEW 1). DO NOT USE A LARGER DIAMETER CUTTING WHEEL.

15. USING A HEAT GUN TO SOFTEN THE PLASTIC CASE, PULL BACK THE ACCESS DOOR ON THE UPPER EVAPORATOR CASE CAREFULLY TO PREVENT BREAKING THE CASE. REACH IN CAREFULLY AND REMOVE THE HOLDING CLAMP SECURING THE CAPILLARY TUBE TO THE EVAPORATOR OUTLET TUBE. BE CAREFUL NOT TO DAMAGE THE CAPILLARY TUBE. DISCARD CLAMP. 16. USING A HEAT GUN TO SOFTEN THE PLASTIC CASE, PULL BACK THE ACCESS DOOR ON THE LOWER EVAPORATOR CASE CAREFULLY TO PREVENT BREAKING THE CASE (FIG. 2). REACH IN CAREFULLY WITH TWO SMALL ADJUSTABLE WRENCHES AND LOOSEN THE FITTING ATTACHING THE TXV TO THE EVAPORATOR INLET TUBE. IT WILL REQUIRE A 7/8" CROWS FOOT EXTENSION TO LOOSEN THE TXV OUTLET JOINT FITTING HIDDEN BEHIND THE TXV ITSELF. REMOVE AND DISCARD THE TXV. 17. REMOVE ORIGINAL O-RINGS FROM THE EVAPORATOR TUBES AND REPLACE WITH NEW O-RINGS THAT HAVE BEEN OILED WITH 525 VISCOSITY REFRIGERANT MINERAL OIL. DO NOT USE PAG LUBRICANT. 18. INSTALL THE NEW TXV TO THE EVAPORATOR TUBES BEING CAREFUL NOT TO DAMAGE THE O-RINGS. FINGER TIGHTEN THE JOINTS AND THEN TORQUE THE JOINTS, USING A BACKUP WRENCH TO HOLD THE TXV IN POSITION TO: INLET 20-35 N.M 14-25 LB.FT. OUTLET 15-22 N.M 11-16 LB.FT. 19. PULL BACK ACCESS DOOR ON THE UPPER EVAPORATOR CASE CAREFULLY TO PREVENT BREAKING THE CASE (FIG. 1). ALIGN THE TXV CAPILLARY AGAINST THE EVAPORATOR OUTLET TUBE BEING SURE NOT TO DAMAGE THE CAPILLARY LINE. PLACE THE FIRST HOLDING CLAMP SO IT IS LOCATED 1/4" OR LESS BELOW THE CRIMP IN THE CAPILLARY TUBE (FIGURE 3). INSTALL THE SECOND CLAMP 1/4" OR LESS BELOW THE FIRST CLAMP. BE SURE THE CLAMPS ARE FULLY SEATED ON THE TUBE AND THAT THE CAPILLARY IS RETAINED IN THE FORMED SEAT OF EACH CLAMP (FIG. 3, SECTION 1-1).

NOTICE: AFTER ALL COMPONENTS ARE INSTALLED, EVACUATE AND CHARGE THE A/C SYSTEM. LEAK TEST ALL JOINTS THAT WERE OPENED.

20. USING A HEAT GUN TO SOFTEN THE PLASTIC CASE, CLOSE BOTH ACCESS DOORS AND ALIGN THE EDGES OF THE PLASTIC. USING A SOLDERING GUN, MELT BOTH EDGES OF THE CASE TOGETHER ALONG THE FULL LENGTH OF THE CUTS, AS SMOOTHLY AS POSSIBLE. 21. COVER THE SOLDERED CLOSURES WITH DUCT TAPE TO PREVENT AIR LEAKAGE. 22. REINSTALL THE RIGHT SIDE TRIM PANEL, THE D-PILLAR TRIM, THE C- PILLAR TRIM, THE C-PILLAR SEAT BELT RETAINER AND THE REAR BENCH SEAT.

PARTS INFORMATION

P/N DESCRIPTION QTY 52450767 OR 52470592 FILTER 1 1134328 COMPRESSOR 1 52469382 THERMAL EXPANSION VALVE 1 3096068 ORIFICE TUBE 1

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OP DESCRIPTION LABOR TIME USE PUBLISHED D4440 COMPRESSOR ASSEMBLY-REPLACE LABOR OPERATION TIME

D3220 VALVE, EXPANSION-REPLACE 1.7 HRS.

FIGURES: 5

CAPTIONS: FIGURE 1 - EVAPORATOR CASE MODULE, TEMPLATE PLACEMENT 1. UPPER EVAPORATOR CASE 3. UPPER TEMPLATE PLACEMENT 2. LOWER EVAPORATOR CASE 4. LOWER TEMPLATE PLACEMENT

FIGURE 2 - ACCESS TO TXV AND CAPILLARY HOLDING CLAMP 1. TXV 3. HOLDING CLAMP 2. A/C TUBE 4. CASE WALL

FIGURE 3 - PLACEMENT OF HOLDING CLAMPS 1. A/C TUBE 4. SECONDARY HOLDING CLAMP 2. CAPILLARY CRIMP 5. CAPILLARY TUBE 3. PRIMARY HOLDING CLAMP 6. TXV

FIGURE 4 - UPPER EVAPORATOR CASE TEMPLATE

FIGURE 5 - LOWER EVAPORATOR CASE TEMPLATE

GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A "DO-IT-YOURSELFER". THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS THAT MAY OCCUR ON SOME VEHICLES, OR TO PROVIDE INFORMATION THAT COULD ASSIST IN THE PROPER SERVICE OF A VEHICLE. PROPERLY TRAINED TECHNICIANS HAVE THE EQUIPMENT, TOOLS, SAFETY INSTRUCTIONS AND KNOW-HOW TO DO A JOB PROPERLY AND SAFELY. IF A CONDITION IS DESCRIBED, DO NOT ASSUME THAT THE BULLETIN APPLIES TO YOUR VEHICLE, OR THAT YOUR VEHICLE WILL HAVE THAT CONDITION. SEE A GENERAL MOTORS DEALER SERVICING YOUR BRAND OF GENERAL MOTORS VEHICLE FOR INFORMATION ON WHETHER YOUR VEHICLE MAY BENEFIT FROM THE INFORMATION.

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