The Jeep Grand Cherokee has an ongoing problem with the harness connector-to-blower motor control module overheating and melting. This causes either intermittent or no operation. Because of this persistent problem, Jeep has a replacement harness connector. This is not to say that the blower motor or control module is problem-free; they could also be problematic. The control module is found in the automatic zone control with infinite temperature control similar to a home thermostat.
Inspect the control module electrical connector. The control module is located on the floor, under the center of the dash and on top of the hump in the floor. Pull the electrical connector out of the control module and inspect it for overheating. It will appear melted if this is the case. This is the most common problem with this system.
Cut the wires behind the burnt connector, one at a time. Connect the new harness. The new harness has all green wires, so use the location of the wires relative to their position in the connector. Orient the new connector the same way as the existing connector. Start on one side. Cut the wire and strip the insulation off the end and install a length of shrink wrap. Insert the end of the wire into the provided butt connector and crimp it with the wire crimpers. Make sure it is tight and that it does not move in and out of the connector. Slide the shrink wrap over the butt connector and heat it up with a lighter to shrink it. Repeat the process for the other two wires.
Check the control module for input voltage, using the voltmeter by placing the voltmeter on 20 volts and connecting the black lead to a good ground. Probe the three-wire connector on the module with the red lead. You are looking for 5 volts at one of the end wires. Turn the key and the fan on. If 5 volts are present, check the control module middle wire for modulation. This means that the voltage will be moving up and down the 5-volt scale rapidly as the module pulses the duty cycle to ground. The blower motor controller will send 5 volts to the control module, which in turn grounds the blower motor through cycles dependent on the position of the potentiometer blower motor switch. If there is not 5 volts present, there is a wiring problem. If the voltage is present but the module does not show varying voltage to ground when probed, the module is faulty and needs to be replaced.
