When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Ok, i have a unique one here. I have a 1998 vette with duel climate control and i have 0 fan speed at all settings. The blower motor does work as tested by grounding out the body i get full speed. I have pulled the blower resistor plug/harness and probed with T pins the tan wire (voltage signal from main control unit) and black ground wire (the ground that i also confirmed that it is a good ground) and ran it through all the speeds and get no voltage from said tan wire. I have pulled the HVAC control unit and did a continuity test on the tan wire and the wire checks out good. I'm left to think it is the HVAC control unit itself that is bad..... any other tests i can do?
The blower ground is a "block ground"...G203...looks like it goes through a splice pack (SP202)….these grounds are for my '01...if you take your DVOM and read say 12.6 volts at the battery what do you read between the red wire (from fuse 51) and the black wire (the ground) ??...should be 12.6 volts...if you're using T pins you look like you know your way around an electrical circuit...I use an old headlight bulbs of different wattages
(see pic) connected to battery positive and the ground wire connected to the whichever ground I'm testing...this is the ONLY way to check grounds...not a resistance check...you have to load the ground circuit !!...I don't know the exact amperage the blower motor draws but a 55 watt bulb (4.5 amps) will probably be good for testing !!...oh, BTW if you had a Tech 2 or any bi directional scan tool you can nail down a bad HVAC control head in a few minutes !!
Most of the time that blower module is the issue. Its a special module that modulates the output signal to control fan speed. There are several SCRs that can crap out and sometimes when they go bad, they vaporize the circuit trace on the circuit boards for the output to the motor. It easy enough to check them and you can repair the board most of the time with magnet wire and some solder.
You can remove that module and it is very easy to open. There is two sides to the circuit board. The control side and the output side. GM even colors each side differently. Usually when it is bad, it is pretty obvious. Most of the time the smell gives it away. LOL!
There are three screws that secure the module to the under side of the air box. You only need to remove the front screw and just loosen the two rear ones.
Unfortunately, that module is expensive. The manual HVAC control one is simple resistor board and is cheep. Don't fall for cheep and get the wrong one. It will NOT work!
That's right...you said you checked the TAN wire (control) and not reading any voltage there going through all the speeds...I believe that is a PWM signal so you should see anywhere from .5 volts to 5 volts or so as you toggle through the speeds...I would follow BC's suggestions !!
I know this may sound stupid but I have has a similar problem with my blower. The blower had no power , the hvac control showed the blower fan was on and indicated different speeds. as I was looking for the problem I moved the wire harness at the BCM and the blower came on. I found a loose connection at the module Bill was talking about
HVAC Blower not working
