Motor Blower of AC

An most cases, the blower motor moves air inside a vehicle for air conditioning, heating and defrosting. A blower switch(in dashboard) is used in conjunction swith resistor block to control fan speeds. The resistor block consists of two coil-wound wire resistors connected to terminals. These resistors drop the voltage and reduce the current to the motor, causing it to turn more slowly. The blower switchs directs current through one resistor to run the motor at low speed, through one resistor to run the motor at medium speed, and directly to the motor to run the motor at high speed.

Some computer-controlled blower motor system have eliminated the blower motor resistors. Instead of varying current through the motor with resistors, the current is pulsed trhough the motor. The speed of the motor is hanged by veryingthe amount of ON time as compared with OFF time. This has the same effect as using a resistor to change the current through the motor. This type of control is easy for computers to perform and reduces current draw on alternator due the ON-OFF pulse instead of continous current flow