I know the problem is intermittent and I don't know if this info will be useful or not. Just disregard if it's not. It's from the service manual.
BLOWER MOTOR OPERATION
The blower motor is used to control the velocity of air moving through the HVAC housing by spinning the blower wheel within the HVAC air inlet housing at the selected speed or, in the ATC system, at the selected or programmed speed.
On models equipped with the manual temperature control (MTC) heating-A/C system, the blower motor will operate whenever the ignition switch is in the On position and the blower motor control in any position except Off. On models equipped with the automatic temperature control (ATC) system, the blower motor will operate whenever the ignition switch is in the On position and the A/C-heater control power is turned on.
For the MTC system, blower motor speed is controlled by directing the ground path for the blower motor through the correct resistor wire to obtain the selected speed.
For the ATC system, blower motor speed is controlled by the blower motor power module which provides the blower motor with power and a path to ground. The blower motor power module also sends a blower control signal to the A/C-heater control. Using input from the blower motor control (manual mode) or sensor data (automatic mode), the A/C-heater control processes the blower control signal from the power module and sets the speed at which the blower motor will run.
The blower motor and blower wheel are factory balanced and cannot be adjusted or repaired and must be replaced as an assembly if found inoperative or damaged.
Possible causes of an inoperative blower motor include:
Inoperative blower motor resistor or power module (depending on application)
Inoperative blower motor switch
Inoperative mode control switch
Inoperative blower motor
Inoperative blower motor circuit wiring or wire harness connectors
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