Heat, ventilation and air conditioning (HVAC) systems are an important part of a vehicle, not only for driver comfort, but also for safety. An operational HVAC helps keep the operator comfortable and more alert. HVAC systems are also a critical part of the vehicle's defrost and defog system, using heat and air conditioning as necessary to clear the vehicle's windshield and maintain visibility. The system is critical, and correct operation of the blower fan is required in most states to pass state inspection. The GMC Canyon blower fan switch, or control module, changes the resistance in the circuit to change the speed of the blower.
Turn the ignition key on. Operate the blower motor switch in all positions. See if the blower fan works in any position at all. If the blower fan does not operate in any position, troubleshoot the blower motor and blower motor circuit.
Raise the hood of the vehicle. Locate the blower fan motor resistor block. It is under the hood, inside of the heater box close to the blower fan.
Unplug the connector from the blower fan. Use a small screwdriver to pry the connector apart gently, while pulling on the tab that is part of the connector to release the latch. There are four terminals on this connector.
Examine the blower fan connector for heat damage, melting or corrosion. If damage is found, replace the blower fan connector before continuing.
Connect the ground clamp of your test light to the terminal labeled "B+." This is the ground. With the fan switch in each "on" position, one of the terminals should light the test light when touched. If the test light does not light when touched to any terminal through the four settings of the fan switch, the problem is in the blower control circuit. It could be a short circuit, broken wire, faulty blower fan switch, or faulty HVAC control module. Otherwise, the problem is the blower fan resistor, and the resistor needs to be replaced.
Remove the positive battery terminal. Connect the negative lead of your digital multi-meter to a metal part of the vehicle. Set the meter to check for "ohms" (electrical resistance) or continuity. Test each of the terminals on the connector by touching each terminal with the positive lead of the multi-meter. The meter should read infinite ohms, or zero continuity. If it does not, there is a short circuit to ground present, and the wiring needs to be checked. If the circuits check with no continuity, the HVAC control module, or the fan switch, needs to be replaced.
