Bring a jumper wire from bat + to the resistor behind l/headlamp. Key OFF

Touch one side for low fan , the other for high.If YES, then the problem is upstream from Resistor.

Jumper the sw at drier that has the 2 6" pigtail wires .
That is low fan.
If yes, sw. is bad or a/c system is low on refrigerant.
Key ON

Unplug blue 2 wire coolant temp sensor w/key ON, this will get high fan.

Report findings

__________________
A Dalton