A good customer came in with her 2000 Buick Century and complained that the blower would not turn off even with the key off. The car has manual HVAC so I was already sure that the blower relay that is built into the blower resistor assembly was stuck. No big deal I have changed dozens of them. I went under the passenger side of the dash unhooked the wiring, the blower went off as suspected so I removed the forward screw. Unhooked the wiring to the blower motor and firmly wiggled the resistor off of the two rear screws. The resistor has slots in it so it is easier to remove the resistor and then loosen the screws with the resistor out of the way.
I quickly hooked up the new resistor to make sure all was well when I found I had only two speeds working. As a cautionary note I made sure the resistor was clear of all objects and as I turned the key on, I ran the blower switch through all speeds and then turned the key off immediately so that I would not damage the new resistor. The whole operation takes about 5-10 seconds if properly prepared. You can also see that the new resistor has a heavier design than the original. To order a new resistor please
Time to test the wiring to see what was going on. Power on the first wire with the key on. Good!
No power on the next wire. Bad!
Power again on the fourth wire but no power on the remaining wires. With this knowledge and years of experience I determined that there was a problem at the blower switch. Because of the split in the wires that had power I knew that both fuses involved in the blower circuit were okay and there was power at the blower switch. The problem had to be at the switch or in the wiring between the switch and resistor. Time to pull the switch out and inspect. First I removed the lower attaching screws at either side of the center dash panel.
I then firmly grasped it and pull the panel away from the dash to release the spring clip retainers. You can see one of the retainers to the left of my thumb.
I then removed the two attaching screws.
Tilted the panel out and tested the wiring the same as I did at the resistor connector with the same results. I did this by lightly back probing the wires. Unfortunately I could not do this and take a picture and no one else was around to do it for me.
Anyway I replaced the faulty switch and retested the wires at the blower resistor connector and all passed.
I finished the job by installing the new blower resistor and also checking and replacing the cabin air filter. To see that procedure click here.
I thought my blower problem (2002 Grand Prix) was fixed after replacing the blower and relay but now it only works on hi speed and after a delay. Retesting the CTRL HVAC fuse reveals no voltage with key off, 4 V with engine and fan switch on hi (with no fan movement), and 12 V with the key turned to the on position without starting the engine. Interesting the blower always works in this position. Is this sounding more like an ignition switch problem? (AC and rear defog LED lights on control panel were working intermittently and now are not working at all).
Thanks, TK
Terminal “G” has power at all times. terminal “E” should have a ground at all times and the remaining have switched ignition power from the blower speed switch as you listed. My gut feeling is that there is a loose connection on terminal “E” in the seven wire harness connector. I do recommend testing at the seven wire harness with it disconnected from the blower resistor. At least as part of the first steps.
Point of clarification.
When testing and retesting the harness to the relay, was the key on? Did you test with the air control in the “forward defrost” mode (and does it matter)? Did you check power at the harness at different fan speeds? My blower does not work at all. The blower and relay have been replaced and it still doesn’t work. With the key on and the “forward defrost” mode chosen I get the following activity at the relay wiring harness:
Fan speed 1 – terminals A and G 12V
Fan speed 2 – terminals B and G 12V
Fan speed 3 – terminals D and G 12V
Fan speed 4 – terminals C and G 12V
Fan speed 5 – terminals F and G 12V
There is power at the CTRL HVAC fuse.
Any thoughts on diagnosis? Since there is power to CTRL HVAC I’m assuming the ignition switch is working. G200 ground looks tight. That leaves the control switch in the dash. Are the meter readings at the relay harness consistent with a control switch problem?
Thank you,
Tom
I’m adding this site to my favorites. I’ve been searching and searching, youre the only guys to show pghotos and give really clear instructions. THANKS SO MUCH, I’m off to try now.
Thanks sparky! I just replaced my A/C switch with help from your post! Too easy!