my air/heater was workin fine but now everytime i start my car it automatically blows n will not let me turn it off nor on! please tell me what causes this

Do you mean it won’t let you turn it off? 'Cause you said it is stuck on - or did you just mean it is on but you can’t adjust the speed?

Anyway, you probably need a new switch in the dash. But you’d also want to inspect the wiring. Or is this an automatic climate control type of system?

exactly it wont let me turn it off. it wont let me turn it down up off nothing! but when i turn my lights on the panel around heater lights up but its off in the middle just dark. i no it doesnt ake much sense but thats the problem. how do i tell if its a automatic control system?