This 2002 GMC Envoy came in with the complaint of the two lowest blower speeds missing. Because one of the lower speeds worked along with the high speed I knew that both fuses were good and I went directly to the blower resistor which is very prone to failure. The blower resistor and the blower motor are both located on the passenger side of the vehicle. By the way, this repair applies to 2002-2009 Chevrolet Trailblazer and GMC Envoy, 2004-2007 Buick Rainier and 2003-2008 Isuzu Ascender models.
First I removed the lower dash trim panel by removing the two attaching screws.
The blower motor is to the right side.
The blower resistor is slightly to the left of the blower motor and towards the firewall.
Next I removed the connector at the blower motor. Using a small screwdriver from the underside of the blower motor, I depressed the retainer.
With the retainer released, I pulled the connector from the blower motor.
A side view of the blower motor and connector.
A view of the connector retainer that has to be depressed.
I next disconnected the seven wire connector to the blower resistor, removed the two attaching screws and removed the resistor assembly.
Here is a look at the old style resistor.
And the new style replacement resistor. To order these parts please click here.
I reversed the procedure and all tested okay. Normally I would have replaced the harness connector as part of the repair. However since there was no damage and the customer insisted on not replacing it I did not. Hopefully it will not burn out very soon. It is documented on the repair order that the customer declined the repair and therefore there is no warranty.
Actual testing of the wiring is as follows. Disconnect the 7 wire harness connector and inspect. If there is any sign of heat damage replace both parts per above instructions. If there is no sign of heat damage then check the following. With the 7 wire harness disconnected check for power on the red wire. It should have 12 volts at all times and it gets it’s power from the 40 amp blower fuse in the under hood fuse box. Next with the key on check for 12 volt power to each of the following wires as you move the blower speed switch from low to high. Yellow / low, tan / med 1, lt blue / med 2, purple / med 3 and orange / high. If any of these signals are missing you will need to inspect the HVAC fuse in the interior fuse box ( under rear seat, driver’s side). If the fuse is okay you will need to check the blower speed switch.
- Terminal “A” Tan = Speed 2, power through blower switch from HVAC fuse
- Terminal “B” Yellow = Speed 1, power through blower switch from HVAC fuse
- Terminal “C” Purple = Speed 4, power through blower switch from HVAC fuse
- Terminal “D” Lt Blue = Speed 3, power through blower switch from HVAC fuse
- Terminal “E” Black = Blower system, ground at all times
- Terminal “F” Orange = Speed 5, power through blower switch from HVAC fuse
- Terminal “G” Red = Speed 5, Constant power from BLWR fuse under hood
If all of the tests above are okay and you want to go a step further, place a test light or voltmeter in the wires going to the blower motor. If the light comes on or you have a 12 volt reading, the resistor and wiring are okay and the blower motor is faulty. This can also sometimes be confirmed by bumping the blower motor with the switches on. If the motor starts after bumping the motor is faulty. One can also remove the blower motor and apply 12 volts (power and ground) directly to the motor. Be careful though the motor will tend to jump and roll all over the place. Hold it firmly and be sure you are clear of the impeller as it could hurt you pretty easily.
One other note. If you have an amperage gauge, test the blower amperage draw while it is mounted in the blower case. Turn on surge amperage could go up to about 28 amps. Amperage draw at high blower should be in the 18 to 24 amp range. The lower the better. Restricted cabin air filters (if present) and dirty evaporator cores will cause a blower motor to draw more current while reducing air flow volume. These two conditions combined will significantly reduce the life of any blower resistor.
This is a great article!! My blower quit working suddenly on all speeds. Following your detailed instructions, I pulled the resister and found the ground wire was burnt. Replaced the pigtail and resister and all is well. Thanks for all the great info.
The black wire terminal “E” is the ground for the blower motor and the blower relay. It has a substantial load on it and is the first terminal to weaken from heat build up. The correct repair is to install a new resistor and connector harness at the same time. They need to be high quality parts and the latest design. The following address is a link to a repair kit with all parts needed. You may also want to consider replacing the blower motor if your vehicle mileage is any where near 150,000 miles. You will need to copy and paste the address.
http://store.the-electric-connection.com/trailblazer–envoy-blower-resistor-with-4180-repair-harness-combo-p569.aspx