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Re: Heater/AC fan does not blow on two lowest speeds.
Your fan uses resistors to reduce the speed of the fan. Hi speed doesnt use the resistors and that is why it runs on hi. Standing in front of the car, all of your heater housing is on the left side of the firewall You will see a connection with about 4 wires That look like they go nowhere. Take the couple screws out and pull it out. You will be able to see the burnt one.Jump out the burnt on and that will give you another speed or two.
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It may be the bearings in the motor are dry or out. You coulod pull the motor and fan assembly out and check its operation while it is out of the heater case. Look for anything inside the heater cavity where the motor sits for any problem hindering motor operation.
The fan uses a resistor block that creates the various fan speeds. It sounds as though the lower two fan speed resisitors are broken. This means you will have to replace the fan resistor block. The only other possibility would be the fan switch on the dash you use to set the speed. It is most likely the resistor block, but if you are handy with a test light, you can verify the switch is good or bad, or take it to your favorite mechanic and have him or her verify.
The lower speeds are accomplished by running the power supply through various resistors that drop the voltage which makes the blower turn at different speeds. The lowest setting uses all the resistors to drop the voltage as much as possible to turn the blower as slow as possible. High speed uses no resistors so the blower gets full power and turns as fast as possible.
Since speed 1 and speed 2 use the speed 3 resistor to drop there voltage and speed three is not working as well my guess is the speed three resistor is burnt out in the device referred to as the blower motor resistor or blower motor speed control module. This is located near the blower motor and is held in place with 2 screws. There will be several wires and possibly two connectors plugged into it.
These are really common failures in many vehicles. The parts are usually available at your local auto parts store and they are typically not that expensive.
the blower motor has no affect on the AC system, start the engine and turn on AC and watch the AC compressor to see if clutch engages,if it doesn't the system isn't full,if you are correct the clutch should be engaged and should quit when you change heater speeds,
Usually when the blower fan only operates on hi speed, its because of a failed blower motor resistor. You still have hi speed because on hi, the power going to the blower motor goes directly to it, as opposed to the lower speeds, when the power is routed through the resistor, thus lowering the voltage, which in turn lowers the speed of the fan. The resistor is usually located near the blower motor itself, under the hood back near the firewall.
The resistors are in circuit only on the lower fan speed settings.
On the highest speed setting, power is switched directly to the fan motor.
Check fan power supply fuses,
Check power is available to the fan when high speed selected.
If all above OK, apply power directly to the motor to verify fan motor runs- if it doesn't the motor may need replacement/repair.