NG 900/9-3 Fan Resistor Replacement
Contents
Overview
The radiator cooling fan uses a resistor in series with the fan motor to regulate the low fan speed. The resistor and wires are exposed to heat from the exhaust manifold. Failures are fairly common, and the resistor is not available separately from the fan assembly.
Replacement
Parts
Original wire size corresponds to about 12 gauge (white, green/white and black) and 14 gauge (green).
- 0.2-0.25 Ohm, 50-75W resistor
- White & Black wire, 12 AWG, automotive
- Green wire, 14 AWG, automotive
- M6 screws and nuts (2)
- 14 AWG crimp connectors (6)
- Heat shrink tubing
- Aluminum plate, 30 x 100 mm (~1.25 x 4")
The heatsink was cut from bulk stock and drilled & tapped in a machine shop, but the same thing can be done with hand tools.
Resistor Location
The resistor is located in a lower part of the cooling fan shroud, attached to a bracket. The resistor is inside the copper colored tube, with wires running to the fan motor and to two connectors. The black connector is for the fan low speed (green) and ground (black) wires. The grey connector has a single wire (white) for the high fan speed.
Fan Shroud
The picture at left shows the shroud with the fan assembly removed. Separating the fan and the fan shroud is not normally necessary to replace the resistor, but the picture shows the resistor mounting bracket molded into the shroud, and two mounting holes.
Replacement Resistor
Any power resistor in the range of 0.2-0.25 ohms, and 50-75 watts. The resistor on the left is a common size used in audio equipment with an aluminum heatsink, Dale RH-50, 0.2 Ohm, 50W. Shown alone, and mounted on a small aluminum plate cut to fit into the same space as the Saab stock part.
Completed Resistor Kit
The complete kit including resistor, heatsink, wires and mounting screws. The yellow splices on the left are for the connectors. The two wires on the right are the motor wires which will be cut to the correct length after the resistor is mounted on the fan shroud. A commercial kit would use machine assembled parts, but the end result is the same.
Attachment to the Shroud
The resistor and heatsink can be mounted on the fan shroud with two bolts (M6 or 1/4-inch will fit the original mounting holes). In the pic at left, the resistor is shown without wires to make the bolts easier to see. The plastic rib the heatsink is attached to is shaped like a fin to help direct air from the fan around the resistor.
Final Assembly
The failed resistor and wires are cut out, and the new kit is crimped to the ends of the original wires. If only the resistor is being replaced, the black ground wire can be left intact. In this case the original wire insulation was in pretty sad shape, so all the motor wiring was replaced. Heat shring tubing was used to cover the wire splices to help protect the wire ends and avoid any chance of shorts.
