The navigation screen went black. And the air conditioner is set on high, but I am unable to control it.
It sounds like two separate problems. Check your fuses for the radio and navigation. If it is the unit itself that is faulty, there are specialized places that will repair them, or you could replace it with a good used one. The blower motor speed is computer controlled on your car. There is a module built in the the motor assembly that regulates the speed via a signal from the main AC module. It could be the motor itself, the AC module, or wiring. I would recommend having a certified mechanic inspect your electrical system to determine what is causing the troubles.
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