Drained and refilled 93 Classic and it heats up fine. Jet pump control causes motor to hum but nothing else. It has frozen in the past and repair folks put a wrench somewhere to loosen up what apparently is a rusted motor. Any advice on what I can do to free up the motor?

Sounds like you have an air lock. Turn off the power, take the access door off and look for the biggest of any pumps inside. There will be a pipe going in, and a pipe going out. Locate the higher of the two pipe connections, and back off the union where the pipe connects to the pump until some water comes out, re-tighten and try the pump again.

If the pump is just humming and the shaft is not turning, you can take the back cover off the motor (where the wiring connects) and access the back of the motor shaft. It should either be slotted for a screwdriver or shaped for a 7/16" or 1/2" wrench. Give it a quarter turn or so and try the pump again. If it continues to not turn you may need to replace the motor.