I have a very original 61K miles z28, 350/4 speed, motor never apart, engine bay never molested, it is as left factory, 1 repaint. heater/AC fan speed switch is acting up and is stuck always blowing on low. To go along with this it will not blow heated air either and just waiting for good weather to go out and see if the cable has come off the damper door. Where would be a good place to start regarding the blower motor switch?

 

https://www.ebay.com/i/401521592113?chn=ps

 

Only working in low, I would suspect the blower relay more than the switch. FYI, I'm not talking about the fan speed resistor.