LOSS OF HVAC VACUUM (NEW CHECK VALVE AND HOSE)

Model and Year: 1991 B CAR

Some of the above vehicles prior to VIN MW121057 may experience a loss of HVAC vacuum. This vacuum loss may cause the heater or air-condition modes to change and/ or the slow operation of the vacuum actuating valves on the HVAC module during medium to WOT (Wide Open Throttle) conditions.

CAUSE:

A leak in the check valve inside the vacuum tank that is located on the top of the HVAC module.

CORRECTION:

This condition may be addressed by installing the following service parts in the HVAC vacuum supply tube at the front of the TBI unit on the engine, as shown in Figure 1.

Service Parts:

Quantity Part Number Part Name -------- ----------- --------- 1 497853 Check Valve - Vacuum

1 1 1/4 in. length Hose - Vacuum 5/32 in. I.D. of *9438381 or Resistant to Fuel and Oil the Equivalent

*GMSPO Service Part Number in 25 ft. roll

Parts are currently available from GMSPO.

PROCEDURE:

1. Remove the air cleaner.

2. Disconnect the HVAC vacuum supply tube at the front of the TBI unit, as shown in Figure 1.

3. Install the 1 1/4 in. length of hose on the black side of the check valve.

4. Install the hose and check valve to the TBI unit, as shown in Figure 1.

5. Connect the HVAC vacuum supply tube to the check valve, as shown in Figure 1.

6. Reinstall the air cleaner.

7. Check the HVAC system for the function and proper mode operations.

Labor Operation Number: T1591

Labor Time: 0.4 Hours

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.