Caprice Wagon RWD V8-305 5.0L (1991)
Vacuum Check Valve HVAC: All Technical Service Bulletins
A/C - Modes Change/Slow Vacuum Valve Operation
Number:
91-08-1A
Section:
1A
Date:
April 1990
Corp. Bulletin No: 031102
Subject:
LOSS OF HVAC VACUUM
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:
Figure 1
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
i
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
