Anyone ever seen this? Weird HVAC issue.

[JEFFSSSEI]

So if I get into my car and start it with A/C set to auto and XX temp the blower motor will not come on, the rest of the unit acts like it's running, however if i then shut the hvac head unit off and back on...the entire system works perfectly fine (blower runs, cycles through all the speeds if set manually, ramps up and down properly in auto mode etc.) until I shut the car off, then wash rinse repeat...it's not a deal breaker/must fix now thing, but it is quite annoying on hot Texas days. Oh and it does the same thing in heating mode as well.

Things I have done:
1. Disconnect the batter for 1hr (no change)
2. hooked up with Autel and did test and calibration of A/C system and all actuators (no change - but mode actuator is sticking/not working correctly and is on order)
3. Swapped out hvac head unit with spare (working pull from old/other car) (No change).

So any ideas or am I just "lucky"?

P.S. To my knowledge I have no other electrical issues or gremlins with the car.

[JEFFSSSEI]

Yay, so it's just me...well if/when I figure it out, I'll report back (and probably change the title to match the issue).

[nos4blood70]

Does it always act exactly this same way? Have you noticed erratic blower behavior over bumps?

[JEFFSSSEI]

Does it always act exactly this same way? Have you noticed erratic blower behavior over bumps?

Yup exact same way every time, no erratic blower behavior, all speeds work (once you turn it back on) manually or in auto mode...my first thought after ruling out the head unit was the blower control module (I believe these have a module vs a resistor IIRC), but I have no other signs of issue with it...it's just weird.

[JEFFSSSEI]

Does anyone have the GM "Description of Operation" for the HVAC system from GMSI? it might give me a clue as to what step in the operation I am missing (long shot I know).

[harofreak00]

I'd replace the IPM as that is what actually is the brain of the system. The climate panel is just the display.

I've attached the Description of Operation as requested along with the blower motor schematic.

[JEFFSSSEI]

Thank-you very much Andrew, I really appreciate that.

I am going to verify power's and grounds and continuity on the control wire from the IPM to the blower module as well as other functions of the IPM, to make sure nothing else (haven't noticed any) is DOA functionality wise.

Actually I did note one thing interesting. my Afterblow feature is turned on (I turned it on when I had access to a tech-2) and I know it will turn on for way longer than 4seconds...things that make you go Hmmmm

[harofreak00]

...as well as other functions of the IPM, to make sure nothing else (haven't noticed any) is DOA functionality wise.

The IPM functions include the following:
Ambient light sensor input and twilight delay input for headlights control.
Front HVAC air delivery and temperature controls.
IP dimmer switch input.
Ignition switch headlight control.
Interior lamps switch input.
Key-in-ignition switch input from the ignition switch.
Rear compartment lid release switch input.
Traction control switch input.