The whole hvac system stopped working . Mechanic said " bad blower module" I replaced that ...no change. Since then I have bypassed all modules, fuses and such to the blower motor ,which works fine when supplied w/ direct power. I have checked the hvac fuse and all others, they are all fine. At this point I have the Computer Climate Control unit removed from the dash and have tested the wiring harness which feeds it. With info found on-line I tested for voltage on specific pin numbers of the harness. With the info i have, it seems to check out good. So this leads me to believe that its the CCC unit which is bad. I'm still not sure but it would make sense that with a bad control unit the proper voltage would never make it to the blower module/motor. So that's where i'm at. Any suggestions are appreciated. I'm hoping maybe I just overlooked a relay somewhere.
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RR/HVAC fuse 30amp located in the under hood fuse box. You can check it but highly doubt it's the problem . More then like it's the blower motor control module that's bad .
The auxiliary blower motor is a variable speed fan. The HVAC control module controls the fan speed by sending a pulse width modulated signal to the auxiliary blower motor control module. The auxiliary blower motor control module varies the duty cycle across the auxiliary blower motor in relation to the pulse width modulated signal. The auxiliary blower motor speed can be adjusted from 10 percent to 90 percent duty cycle (PWM), 90 percent is high speed fan.
Watch this video for testing purpose's only , this is a front blower motor control module . Same way your back one works . GM is GM Chevy , Buick ,GMC , Cadillac .
What are you using to test this control signal ? Were you on right wire ?
Blower Motor Control Processor
The blower motor control processor is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive voltage and ground circuits enable the control processor to operate. The HVAC control module provides a pulse width modulation (PWM) signal to the control processor in order to command the blower motor speed. The processor supplies 12 volts to the blower motor through the blower motor voltage supply circuit. The control processor uses the blower motor ground as a low side control to adjust the blower motor speed.
Chevy Trailblazer EXT Blower Motor Won Turn Off The blower motor in this video don't shut off , but he show's how to test the PWM signal right !
Your blower motor control module is probably bad , or HVAC control panel is bad , or a wiring problem !
There is a relay in the under hood fuse box , blower motor relay .When switched to high it energizes the relay allowing power from the HVAC fuse /30 amp to flow direct to the blower motor. from pin 30 to pin 87 , if you look on the side of the relay there is a diagram .For all other speeds the current flows from the switch through the resistor through pin 87a to pin 30 on to the blower motor ! Check the HVAC fuse in the under hood fuse block .IF the fuse is good check for continuity between the fuse side with out B+ that means pulling the fuse and using a volt meter to see which side has power and checking the side that doesn't have power to pin 87 at the relay socket ! Probably a bad fuse or stuck relay . Pull that relay and try a different one. You can get wiring diagram at www.bbbind.com click on technical information ,then click on Technical Service Bulletins & Wiring Diagrams .then on next page go down to the bottom and click on I agree . next page click wiring diagrams ,then just fill in you vehicle information .then HVAC system . click on diagram, then you will see 7 links , click on the 5th one and that's the diagram for the blower motor circuit !
If this a manual HVAC system, the blower motor resistor pack is defective or the blower motor itself is bad. If this is the Automatic digital HVAC, the blower motor control module is defective or the blower motor itself is bad.
my 2000 chevy blazer zr2 4x4 the a/c switch that does 123 and 4,the a/c only works on num 3 setting.ive just replaced the whole a/c sytem and blower relay.it wont work on num 4 at all and when it does it cuts off on its own and then works on setting 3 only?what to do?