Why does the blower not blow on high?

Answer 1

there is a possibility that your speed control switch could be faulty. use a standard volt meter and check the positive leads on the blower motor. turn the blower on a lower setting that you know works. Then check the volt meter reading while the blower is on low.The reading should be lower than 12volts. turn the speed control knob to high to verify you are getting voltage on high. If there is no voltage present on the high setting you need to replace your climate control unit( the speed control unit)

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If the above doesn't work,

Another much more common answer; Had the same situation on 3 of my Crown Victorias, years from 2001-2003, The blower motor resistor may have gone bad. The symptoms are usually 1 or more settings on the blower motor do not function properly. This is located under the hood mounted on the passenger side firewall next to the heater core hoses with four 7mm bolts. This unit normally rusts up and needs to be replaced. The unit is approximately $20 and can be purchased from the dealer. The area is a little tight, but best bet is to disconnect the heater core hoses and put a rag in them to stop the flow of sitting antifreeze. Disconnect the plug on the old blower motor resistor and replace the new resistor. The plugs fry up, so be careful when removing them. The plastic breaks easily.

Be sure to disconnect the negative battery cable before attempting this procedure.