2003 GMC Yukon
So I'm having an issue with my hvac system. It blows intermittently. I can have it on one afternoon (working or not) and it'll just turn itself off and then a few seconds or minutes go by it'll come back on. Everything is new, the blower motor, resistor, plug harness to resistor and control module. Something I noticed even after changing the harness is the plug still gets pretty hot and it has beefy wires too so it's confusing me. Full blast the small wire is getting around 1V to 1.8V. And when off it gets exactly 5V. Power wire is getting 13.5 to 14V. While truck is running. I would assume it's normal voltage. Sometimes when I go to turn on the ac it don't even blow and sometimes it does. Like I said everything is new, the motor, resistor, harness, and module. But as said I noticed the harness still gets pretty hot and I pull it out and it's crispy. When it's off I tend to lean over and unplug it and plug it back in and it works but not for long so maybe it's just that harness again? Or maybe the resistor is pulling too much? The ground wire gets hot im not sure if its supposed to get hot? Any help would be amazing. Thanks
the motor is probably wearing out. Replace it before it roasts everything else.
Every time you turn on the fan, and it's not turning, you're basically shorting out the circuit. Eventually things will start burning and melting.
The motor is new it an oem acdelco motor
then you have bad connection somewhere.
Grab a schematic and use a DMM to measure resistance
When wires overheat it's because of too much current (amp draw) ((short to ground)), or too much resistance in the circuit.
Could be corrosion/heat damage in a wire or connector, a faulty Ground point, or in your case a failing blower motor. But you replaced the blower motor and the problem persists.
You don't have a direct short to ground because you aren't blowing fuses.
So how to troubleshoot this?
Here's how the blower motor is wired.
First let's look at how the blower motor gets Power in all speeds EXCEPT HIGH SPEED.
I highlighted Power in Red and Ground in Green.
In these speeds the High Current Power to the Blower Motor comes from the 30 amp HTR/AC fuse in the Left Instrument Panel Fuse Box and passes through a resistor or a series of resistors (depending on the fan speed selected). The Blower Motor Relay ISN'T energized and Power goes through the Blower Motor Relay through terminal 87A to terminal 30 to the Blower Motor. The Blower Motor is Grounded at Ground Point G200.
Now let's look at the circuit when the blower is switched to HIGH SPEED.
Now, the 30 amp HTR/AC fuse in the Left Instrument Panel Fuse Box isn't Powering the Blower Motor anymore.
Power to the Blower Motor is being provided by a different fuse.
The 40 amp Blower Fuse in the underhood fuse box is providing Power to the Blower Motor. The Blower Motor resistors are being completely bypassed.
The only thing the 30 amp HTR/AC fuse in the Left Instrument Panel Fuse Box is doing is providing Power (low amp draw) to terminal 86 of the Blower Motor Relay coil to energize the relay.
The relay is energized, the internal relay contact switches to create continuity between terminals 87 and 30 and Power goes to the Blower Motor.
This time I'll highlight the Blower Motor relay control (terminal 86) in Pink and again Red for Power and Green for Ground
So is the wiring connector overheating/blower motor cutting off problem happening during both Lower Speed(s) blower operation and High Speed blower operation?
((I'm thinking the blower motor has an internal thermal overload switch that's getting tripped or there's protection built into the HVAC Control Module)).
Regardless, if the issue happens in blower lower speeds AND blower high speed then look for damaged wiring connectors or damaged wiring in this section including that G200 Ground Point and maybe put an amp clamp on the blower motor wire to see how many amps it's pulling.
