1996 Chevy Silverado blower fan high only

I have 1996 chev silverado 5.0 liter. Rainwater leaks into the blower motor housing unit. The water froze and seized the blower motor. I replaced the blower motor and the blown fuse. Now the fan only operates on high. I tried to find the source of the water leak with no luck. My local auto repair shop couldn't find the water leak either. Any suggestions on where the water leakage could be coming from or how to get the blower to work on low? A blower fan that only works on high speed nearly always suggests a burnt-out resistor pack that needs to be replaced. However, due to recent repair work, we cannot rule out either a faulty switch or incorrect wiring. A simple voltmeter test, are you getting voltage, will determine.

As for the leak, wait till warmer weather and see what you can do with a garden hose.