Phase 2 Heater Fan - controller repair how-to - Alfa Romeo Forum
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Join Date: Sep 2011
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916 GTV V6

Phase 2 Heater Fan - controller repair how-to

My phase 2 GTV V6 developed a problem with the heater fan, whereby it would continue running even after the ignition was turned off. Subsequently, it failed completely and started blowing the 50A fuse under the bonnet. The fault turned out to be a partially seized motor and a dead controller.

If your car displays similar symptoms, first check the motor (easy enough to remove - one bolt, check this forum for more instructions).

Then, if the controller still appears to be at fault (especially if the fan runs even with ignition off), it can be repaired instead of replaced, saving money (and the environment!)

The controller regulates current to the motor using two transistors, and these will almost certainly have failed. Given that the controller is permanently 'in-circuit' even with ignition off, if they fail, the motor will continue running, or if the motor seizes, the fuse will blow.

Replacement of the transistors needs some electronics skills. If you're at all unsure, do not attempt, but if you can solder, here's the procedure -

1. Remove the controller (under passenger side dash, by bulkhead). The connectors can be tricky to disengage - use a small screwdriver to release.

2. With controller removed, take the plastic lid off.

3. You'll see a circuit board with two large transistors in the centre, which are held against the heatsink with a piece of spring steel riveted to the heatsink.

4. The rivets need to be ground off, after which the circuit board can be removed.

5. The transistors must be replaced with the correct part - they're IRFZ44 power MOSFETs, available online from CPC-Farnell at the princely sum of £0.79 each (at the time of writing).

6. Given that the two rivets have been removed, you'll need to drill a couple of small holes in the heatsink to accept small self-tapping screws (or you could tap the holes). At the same time, clean off all old heatsink grease and make sure all metal swarf is removed!

7. Cut the old transistors off the circuit board and solder in the new ones, taking care to bend the legs such that the board will correctly line up with the heatsink on reassembly. Take sensible antistatic precautions too - you're handling MOSFETS. It's quite an easy soldering job - the board is good quality and there's plenty of 'pad' material around the transistor legs.

8. Apply fresh heatsink grease and reattach the circuit board to the heatsink. Use threadlock on the screws and as an additional precaution, nail varnish or similar on the heads to prevent the screws vibrating out.

9. Pop the plastic lid back on and all should now be operational. See attached photo of the circuit board I repaired, with the transistors circled in red.

Hopefully this might save you some money - even second-hand controllers are over £20 - but please note I accept no responsibility for any repair attempted. You do this at your own risk - to be honest, I don't like the design at all, and having the controller permanently in-circuit with the ignition off is madness... If you burn your car down, don't blame me...
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cheshirekev is offline  
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Nice to see stuff being repaired & a good write up.

I had a look inside mine when I had the parts lying around before retro fitting to my P1 and identified the transistors as being the likely cause of failures.

pkr is offline  

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