HVAC Air Delivery System Check 1998

The P/B Booster Pump provides vacuum for the P/B Brake Booster and the HVAC controls. The P/B Booster Pump creates vacuum which is stored in the large steel vacuum tank mounted below the rear of the Power Inverter Module (PIM). The P/B Booster Pump will operate until enough vacuum is achieved to open the P/B Booster Vacuum Switch. The P/B Booster Vacuum Switch is mounted to the vacuum canister. There is a secondary plastic vacuum ball canister mounted to the left underside of the hood. This canister is used to provide a reservoir of vacuum for the HVAC controls. A one way valve is mounted between the vacuum source and the vacuum reservoir to prevent the P/B Booster from scavenging this vacuum away from the HVAC control head.

There is a large diameter vacuum hose connected between the large steel vacuum tank and the P/B Booster. A vacuum tee is installed in this line which branches off a smaller vacuum line for the HVAC controls. This vacuum tee is an ideal place to install a vacuum gauge for checking the system. Use a hose clamping tool or a pair of needlenose vice grips to clamp off the large hose between the tee and the P/B Booster if you suspect the P/B Booster is bad.

As an aid in determining whether or not the air conditioning, electrical, air, and refrigeration systems are operating properly, refer to the System Performance table.

The operation of the air conditioning blower at all four speeds, in any position except the OFF position, and the engagement of the compressor indicate that the electrical circuits are functioning properly. The blower should not operate in any speed with the HVAC Mode Control Knob in the OFF position.

The operation of the A/C control selector in the distribution of air from the designated outlets indicates proper functioning.