The following steps outline the process for repairing the variable speed fan control unit, called the "fan speed amplifier" by the Holden parts men, and as fitted to Holden Commodore / Berlina / Calais / Statesman vehicles fitted with climate control. The variable speed control unit occupies the same location as the fan speed resistor in non-climate control fitted cars, but is a more sophisticated (ie more expensive) unit than the more simple resistor unit.
The unit had failed because of a fault in the power transistor, the most likely component to fail. The fan only operated in HIGH speed and would not operate at all on the lower speeds. The lower speeds are those used by the climate control system, while the manually selected HIGH fan speed bypasses the climate control. This operates a separate fan relay, which runs the fan (and the air conditioning) on high speed only.
A replacement assembly from Holden cost in the order of $60-$70, so I thought I might dismantle the faulty assembly to see if it could be repaired. I found the unit clipped and screwed together, so I dismantled it. The control is basically a large aluminium heat sink to which is attached a small printed circuit board and a large power transistor. As all the components looked intact, the most likely cause was a faulty power transistor, which operates at high temperatures.
The transistor is easily identified, being in a metal case as round as a 5-cent piece and screwed to the assembly with two small screws. The make and part number is printed on the top of the transistor, a Motorola unit - part No MJ11032.
I ordered a replacement unit via the web from electrical component supplier Futurlec, at
www.futurlec.com, using my credit card, and it arrived in 6 days from their SE Asian warehouse. I received e-mail updates as to receipt of order and despatch. Cost was $US3.50 plus $US4 postage, a lot less than the complete component cost from Holden.
Replacing the transistor is fairly simple if you can use a soldering iron, and the unit worked perfectly when re-assembled and re-installed.
To repair the unit, remove the control unit as described elsewhere on this site. Sit down at a workbench with good lighting and dismantle the control unit by following these steps:
1. The plastic base of the unit has to be removed. Mark the base and adjacent aluminium heat sink structure to facilitate re-assembly the correct way round.
2. Carefully lever the plastic base off the unit, sliding it along the three power connectors. The plastic base is held in place by four aluminium fingers that also need to be carefully prised out with a screwdriver as the base is slid off.
3. You should now be able to see the small printed circuit board that was covered by the plastic base. Look over the board and make sure that there is no obvious damage (burning or melting) to the board or any of the small components (resistors, capacitors etc). If no obvious damage, then the faulty unit is probably the transistor.
4. Remove the four screws holding the aluminium heat sink together, and lift out the central section. You can now see the top of the power transistor and should be able to read the make and part number on the circular cover.
5. Remove the longer screw from the two that secure the transistor in place. The long screw extends into the printed circuit board and can easily be identified. Leave the other shorter screw in place for now.
6. Place the unit on the workbench with the power connectors pointing upwards. The two wires for the power transistor can be seen passing through the heat sink into the circuit board. They are easy to see and you will not mistake them.
7. Insert a small screw driver under one side of the printed circuit board. Place the tip of the soldering iron on the end of one of the transistor wires and when the solder melts, lever the circuit board up a little. Then do the same with the wire on the opposite side.
8. Repeat this process a couple of times until the circuit board lifts off.
9. Make sure that the two holes where the transistor wires were inserted into the circuit board are clear and not covered with any remnant solder. If not, pass a 1mm twist drill through the remnant solder in the hole. This can easily be done by twisting the drill in your fingertips, as the solder is quite soft.
10. Turn the assembly over and remove the remaining screw holding the transistor in place. Put a small mark on the heat sink to note the position of this screw, as this is the first one that you will need to replace.
11. Carefully prise the transistor off the base. There is a small gasket that fits between the transistor and the heat sink. Remove it carefully from the transistor, as you will need to replace it on the new unit. If the gasket is still stuck to the heat sink, leave it in place, and lift the transistor off it.
12. Clean any remaining solder off the transistor wires and then carefully slide the insulating sleeves off the wires, and slide them on to the new transistor wires.
13. Replace the new transistor on to the heat sink with the gasket in between. It will only reassemble one way.
14. Secure the transistor with the short screw in the location you marked earlier.
15. Place the unit on the workbench with transistor wires pointing upwards.
16. Place the circuit board back on to the heat sink, inserting the two wires into the two holes. Again it can only go on one way round with the other electrical components visible on top.
17. Put the soldering iron to the wires, one at a time, and simultaneously touch them with some fine resin core solder to solder them back to the circuit board. Do not use too much solder, as it must not flow over and touch other nearby components.
18. Replace the long screw securing the transistor in place, noting that this screw passes through the printed circuit board. Touch the top of this screw with the soldering iron and solder as well, as it also forms part of the circuit.
19. Reassemble the heat sink using the 4 screws
20. Align the marks on the base and adjacent aluminium heat sink structure that you made on disassembly, making sure it is the right way round. Slide the plastic base back over the power connectors, pushing the 4 aluminium fingers in place with a screwdriver.
21. Reinstall the unit in the car.
Finally, if you can't get it to work, it has cost you less than $10 to try, and you can always go and purchase a complete new assembly from Holden. However, if you are reasonably capable with your hands, you will have the satisfaction of fixing the unit yourself for a lot less than replacing the unit in total.
Repair of VT Variable Speed Fan Control Unit
Linear Mode
