The heating, ventilation and air-conditioning -- HVAC -- system in a 1997 GMC truck has many components that make it work. However, none of those components matter if the blower stops working. The blower is the part responsible for creating the airflow in the HVAC ductwork. The blower consists of two main parts, the motor and the fan. The motor is a small, high-rpm electric motor that spins the fan. The fan, commonly called a squirrel cage, sits on the motor. It is typically beneficial to replace the blower as an entire assembly, as opposed to individual components.
Open the GMC's hood. Loosen and remove the negative battery cable connector from the battery, using the ratchet and a socket. Place the cable to the side of the battery to prevent it from inadvertently touching the positive cable.
Loosen and remove the bolts holding the truck's PCM, the large, aluminum electrical box near on the passenger side of the vehicle, using a ratchet and socket. Pull out the locking tabs on top of both electrical connectors plugging into the PCM and pull both connectors from the PCM. Lift the PCM from the truck, exposing the coolant reservoir under it.
Loosen and remove the bolts securing the coolant recovery tank, using a ratchet and socket. Only move the reservoir a few inches toward the front of the vehicle; there's no need to remove it from the vehicle altogether.
Grab the blower motor cooling tube, the black, plastic tube running from the passenger fender well to the rear of the engine compartment; pull it toward the rear of the vehicle and out of the engine compartment.
Unplug the electrical connector from the top of the blower motor, located at the rear, passenger side of the engine compartment, by pressing the locking button and pulling the harness from the motor.
Loosen and remove the bolts around the outside edge of the blower, with a ratchet and socket. Pull the blower toward the front of the engine and out of its hole in the plastic case.
Place the new blower into the hole in the plastic case and its bolts, using the ratchet and socket. Plug the wiring harness into the receptacle at the top of the new blower and listen for the click indicating it's locked into place.
Place the blower motor cooler tube back into its hole in the passenger fender well.
Place the coolant reservoir back in its correct position and tighten the bolts with a ratchet and socket. Place the PCM back on top of the reservoir and tighten its bolts with a ratchet and socket. Plug the two electrical connectors back into the PCM and insert the plastic locking tabs to hold them in place.
Reconnect the negative battery cable and use a ratchet and socket to tighten it to the battery terminal. Close the GMC's hood.
