WHISTLING NOISE WITH BLOWER FAN ON (SEAL MODULE SEAMS)

SUBJECT: WHISTLING NOISE WITH BLOWER FAN TURNED ON

MODELS: 1992 C/K AND TOPKICK/KODIAK TRUCKS

Some 1992 C/K and Topkick/Kodiak trucks may make a whistling type noise with the blower fan turned on. Noise may occur in all modes or in only one mode often at higher blower speeds. The cause of the noise is usually an air gap or hole between the module seams.

The noise has often been mistakenly diagnosed as blower motor noise, especially if the gap is located between the scroll cage and the evaporator case. The noise source can often be verified by applying pressure to various places on the module and scroll case and noting a change in the noise. Run- ning a hand along the seams can also produce a variation in module noise. True blower motor noise should remain the same when either of these tech- niques are used.

Areas of the module that contain unheated air are already sealed but may still cause a noise if the sealer does not fully cover the gap.

Most leaks can be found around the tongue and groove joint and can be repaired by separating the module seam, cleaning if necessary, and applying black RTV sealer P/N 12345739 (6/3.35 oz. tubes) then reassembling (Figure 1).

PARTS INFORMATION

Part Number Description Quantity ------ 12345739 Black RTV Sealer Part number is for six 3.35 oz. tubes

Parts are currently available at GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use: Labor Operation Time --------------- ---- D1410 0.5 Hrs.

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.