A/C PERFORMANCE DIAGNOSIS INFORMATIONAL

SUBJECT: AIR CONDITIONING PERFORMANCE DIAGNOSIS (INFORMATIONAL)

VEHICLES AFFECTED: 1991-92 CHEVROLET LIGHT DUTY AND MEDIUM DUTY TRUCK AND GMC LIGHT DUTY AND MEDIUM DUTY TRUCK WITH AIR CONDITIONING (OPTIONS C60 OR C69)

Some owners of 1991-1992 C/K or 1991-1992 TopKick/Kodiak vehicles may conment that their air conditioner is not cooling sufficiently. When investigating air conditioning performance comments, especially if a performance test leads to a diagnosis of no trouble found, be sure the customer understands the intended use of the recirculation ("RECIR") feature (Figure 1).

Selecting recirculation causes the Air Conditioning system to draw air from the passenger compartment rather than from outside the vehicle. As already cooled air begins to circulate through the air conditioner it becomes increasingly easier to dehumidify and cool. This increase in cooling ability can cause center duct temperatures to be 9 to 12 degrees C (10 to 15 degrees F) cooler at 80 KPH (50 MPH) assuming an ambient temperature of 38 degrees C (100 degrees F) and 40 percent humidity.

If a customer desires maximum Air Conditioning performance, be sure they understand the operation of the recirculation ("RECIR") feature.

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.