V40 Heater Fan Bypass?

[Overbomber]

Hi,

I've the dreaded gremlins in the heater fan so it's not blowing, sometimes it's on full blast or it decides to kick in out of the blue etc.

Can I bypass the control so I can, with a separate switch, turn the fan on or off until I can get to Maplins and solder in the new part? I assume it'll be running full blast but these frost mornings are seriously grim without the ability to clear the screen quickly or warm the car up.

It'll be a short term bodge, but necessary, if it's possible,

Cheers

Phil

[DXMachina]

Fan speed control is via an NPN-type power transistor, type MJ802, mounted on a heatsink under the glovebox. If you can get in there and connect a wire to the 'Base' pin and feed it via a resistor (maybe 3 kilohms? not too small or you'd roast the transistor) or variable resistor to the car's positive line - perhaps the radio switched supply as thats nearby - it would probably turn on the fan.

Not sure if other electronic functions would prevent it working or not though. Depends how clever / involved the modules behind the dash are, and whether any other relays or transistors are required to be powered up before the fan spins.

[m1tch1987]

Its a common issue, its just the resistor for the fan speed selector, mines started to do it intermittantly

[mikealder]

Originally Posted by m1tch1987

Its a common issue, its just the resistor for the fan speed selector, mines started to do it intermittantly

What resistor, when I had to fix the wifes V40 earlier this year I replaced the Transistor which is a different component all together.

Go to Maplins and purchase the part as it costs about £5 then attach it to the heatsink and solder the wires to it, refit and the heater blower will work again - Mike

[DXMachina]

It seems that because many cars use resistance banks to control fan speed, the transistor module in an x40 is often referred to as 'the resistor'. Possibly Volvo call it that...

Else it could be a reference to the actual variable resistor mounted in the dashboard - 5 kilohms apparently - which can have flaky contacts after an extended life

[960kg]

Originally Posted by DXMachina

It seems that because many cars use resistance banks to control fan speed, the transistor module in an x40 is often referred to as 'the resistor'. Possibly Volvo call it that...

Else it could be a reference to the actual variable resistor mounted in the dashboard - 5 kilohms apparently - which can have flaky contacts after an extended life

On the X40 heater heatsink under the dash there is a large transistor but if you turn over the block you will see hidden away by the wires a very small resistor, so it does have the two parts on the heatsink.


Overbomber....to bypass the heaterblower switch just find the blower relay in the pic. as this is for the blower full blast only or high speed only.

Buy a decent amperage on/off switch and connect it across the connectors going to the relay.

Drill a hole for the wire through the plastic tray part below the radio and the wire and switch will be easy turned on and off when required.

I will state first of all i replaced the resistor and transistor in the heatsink and also the pots. on the board on the dash and it made no difference to the fan working properly.

If at this stage it is sadly the electrical board has blown parts on it which affect blower and also heat control and i wasn`t prepared to pay £400+ for a new one.

I did this fix on my 2001 1.8 some 2yrs ago and is still like it, works perfectly.

[Overbomber]

Thanks 960kg - this was exactly what I wanted to know - and thanks for the photo. I'm hopefully off to Maplins tomorrow but I want to have a back-up if they don't have the transistor in stock, plus it means I can take my time with the repair and still have some demist/heat control. It shouldn't be too much of a pain to rig up,

Cheers

Phil

[mikealder]

Check the stock in your local Maplins before you leave home as stock checks are possible from their web site - Mike

[Dean1985]

Originally Posted by mikealder

Check the stock in your local Maplins before you leave home as stock checks are possible from their web site - Mike

But not always accurate as I found out once upon a time