CLICK/THUMP NOISE DURING A/C OPERATION

SUBJECT: CLICKING/THUMPING NOISE DURING A/C OPERATION (REMOVE MATERIAL FROM WAFFLED RIBS)

MODELS AFFECTED: 1992-93 ROADMASTER

CONDITION:

--------- A clicking or thumping noise may be heard during A/C operation.

CAUSE:

----- The heater shut off door may be warped and contacting interior surface of HVAC module during door travel from full open to full closed position.

CORRECTION:

---------- This condition can be induced on manual systems by moving the temperature lever from full cool to full warm repetitively. On automatic systems cycle the temperature selector switch from mid-range to full cool several times. If noise is perceived as described, remove material from waffled ribs on heater shut off door face as outlined in the following procedure.

1. Remove A/C Module Lower Evaporator Case per Service Manual, Section 1B. Front screw may be hidden by carpet and difficult to access. Use of a 7 mm flex head socket may be helpful. (See Figure 1 for attaching points.)

2. Disconnect vacuum harness gang plug connector at rear of module. Apply vacuum to the gray vacuum line on the female gang connector to actuate the heater shut off door into the closed position.

3. Spray waffled ribs on heater shut off door face sparingly with tracing powder. Kent tracing powder (P/N 20065) may be used. Kent products distribution can be obtained by calling 1-800-654-6333.

4. Cycle door five (5) times by actuating vacuum pump. Areas of heater shut off door that are in contact with module will be apparent as the tracing powder will be rubbed off.

5. Using a 1/2 inch strip of 60 grit cloth back sand paper, carefully sand down area(s) that are in contact. (See Figure 2)

6. Reapply tracing powder and cycle door five (5) times. Check that heater shut off door is not in contact with module. Also listen to be certain that there is no thumping or clicking sound.

7. Remove remaining tracing powder by using an air hose and wiping with a damp cloth. (Use safety glasses when using air hose.)

8. Connect vacuum gang plugs. Install push pin into module boss.

9. Install A/C Module Lower Evaporator Case per Service Manual.

WARRANTY INFORMATION:

Labor Operation No.: T1953 Labor Time: 1.0 Hr.

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.