Blower Fan not working?

Where is the HVAC modules located? Engine compartment? Behind dash?

Checked module and it had 12 volts on the input but only 1.2 volts on the output to the motor. The module also became warm or hot to the touch. I purchased a new module and plugged it in but the blower still does not work. Apparently the modudle was not bad so where should I go from here?

It was the ground that was loose I got it fixed thank you!

Heater problem V8 Four Wheel Drive Automatic 177000 miles

Issue: Drove the truck to destination and blower worked fine when truck was shut off. Got in it to leave and turned on heat on but no blower. Blower does not run in any of the four positions of the Control Switch. I have checked fuses but all are good. I originally suspected it was the blower motor but now am stumped!

Took the fan motor out and tested voltage. Here's what I saw which, to me, is strange.

There are four "knotches" on the rotary switch corresponding to fan speed. Right? Defined in the schematic as Lo, M1, M2 & Hi. Below is the voltage I see at each setting using a digital meter.

Off - Zero Volts
Low - 8v but climbs slowly to about 9v
M1 - 11.7v
M2 - 11.45v
Hi - Zero Volts
Note: When I turned to a lower setting from any higher setting the voltage drops dramatically and then slowly climbs back to the values from above.

I have now replaced both the Fan Motor, the High Blower Relay with no avail or change in voltages.

I removed the Blower Resistor and check for continuity across all of the various coils and the one resistor. All are good.

The only thing I have not replaced/tested is the HVAC Control Module which includes the rotary switch.

Other notes:

I have checked wiring harness around the heater housing for signs of overheating. No visible signs.
Change other rotary switch for air deflection and the appropriate doors open or close. I can hear them.
The Recirculation button works fine as I can also hear/see the door operate.
Rear AC fan works fine.

Questions:

1. I understand a common problem is that if the resistor goes bad, the fan may only operate on Hi. I am seeing the opposite. Should I be seeing continuity across all poles on the resistor?
2. Couldn't I hook the fan to a 12v power source and it should run? Haven't done it yet, afraid of frying the brushes but seemed like a basic test.
3. Should the HVAC Control Module be the next focus? Is it a pain in the butt to remove?
4. Am I delving too deep here and missing something obvious?

So I'm somewhat stumped. Wondered if you had any specific recommendations based on the above info.

Thank you in advance. Hope you had a great Thanksgiving.

RG

About a week ago I noticed that my fan quit working for about 5 minutes one day. Then a few days later it happened again. Today I tried to run my a/c on full blast and it started pumping out heat. So I turned it off and back on. Now the fan will not work at all anymore. Do you have an idea if it is the blower motor, blower controller, or the resistor?

Heater problem
2004 GMC Yukon V8 All Wheel Drive Automatic 40000 miles
I replaced my switch in the dash and it started working again. Thanks for the great info