My blower motor speed works on low and med. When I move switch to high it will not run. Car is a 1989 Lesabre LN3. Need help.

Check the contacts in the speed relay (engine bay, cowl, passenger side, under the big black plastic cover.) Reseat it a few times and see if your Hi comes back.

There'* two speed circuits for the blower fan. One runs through a resistor block, to give you the speeds other than high. The high speed circuit runs through the relay to the blower motor.