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This could be a few things and it will take some electrical testing to know for sure what is going on.
It could be the control head itself. This isn't likely, but possible.
It could be a short to ground on the control wire between the control head and the blower motor power module. Again possible but not that likely.
The most likely cause for this would be a failed blower motor power module. The power module is what controls blower motor speed based on a signal from the control head. The power module is located in the heater box directly behind the glovebox opening.
could it be in the key switch my boy said the car hesitated when starting once then started blower thing . what kind of money to repair to expect
No, it's not related to the ignition switch. It's a bad blower motor power module, control head, or wiring issue.
The blower motor power module runs about $64.