A/C - Heat fan

COSMIK681

MEMBER
MERCURY SABLE

1990 Sable Wagon - The fan won't blow. I don't if the switch is bad or if it has a short. I checked all of the fuses and they all look okay, but it won't even blow on vent when the car is moving. Thank you for any help you can provide.

Wednesday, October 3rd, 2007 AT 3:34 PM

1 Reply

FAIRRACING31

MECHANIC
150 POSTS

NOTE: The blower motor is switched on the ground side of the circuit.

1. Check the fuses and all connections in the circuit for looseness and corrosion. Make sure battery is fully charged.
2. With the transmission in park and parking brake securely set, turn the ignition switch ON. It isn't necessary to start the vehicle.
3. Locate the electrical connector at the blower motor and inspect it, making sure it is tight and not corroded. Backprobe the connector with a test light or voltmeter. There should be battery voltage at one of the terminal. If not, there is an open in the circuit between the power distribution box and the blower motor.
4. Leaving the blower motor connector connected, ground the wire that runs from the blower motor to the blower motor switch and resistor. If the blower motor now runs, there is a problem in the blower motor switch, resistor assembly or wiring between them. If the motor does not run, it is faulty. Replace it.
The blower motor resistor assembly is located on the evaporator housing under the dash on the right side, near the blower motor. You must remove the glove box to access the blower and blower motor resistror. There are three resistor elements on the resistor board to provide low and medium blower speeds (high speed bypasses the resistor).
The blower operates continuously when the ignition switch is on and the mode switch is in any position other than off.
A thermal limiter resistor is integrated into the circuit to prevent heat damage to the components. If the thermal limiter circuit has been opened because of excessive heat, it should be replaced only with the identical replacement part. Do not replace the blower resistor with a resistor that does not have the thermal limiter.
With the resistor assembly removed from the car, inspect the limiter for damage, indicated by the material melting out of the limiter. Check the resistor block for continuity between all terminals. Resistance between terminals 3 and 4 should be about 1.3 to 1.5 ohms:resistance between terminals 2 and 4 should be 1.8 to 2.0 ohms, and resistance between terminals 1 and 4 should be 2.3 to 2.5 ohms.