M59 Heater Fan Control.

[jericlin]

Hi
Do any members have the correct wiring scheme drawings for the heater fan power supply and controls? 
The Haines manual is useless in this respect. 
My heater fan works spasmodically and is now left switched on all the time 
Switching it off increases chance it won’t switch on next time !! 
The fan supply only goes live after the engine is started ( not when ignition is first switched on ) this would seem to imply that there is a relay that pulls in to connect it once the engine is running. 
Any sleuths out there with more evidence ?

[geoff]

I have little to offer you other than to say it is normal for the fan to only work with the engine running,it can be a nuisance I find after other vehicles but that is how it is.

Speed control is attained by a resistor pack.

There are lots of heater fan posts on the Forum it would be worth a " search " I think.

Others may be along to advise with better information, if you get a result please report back as it will help others in the future and maybe even myself.

[cancunia]

As Geoff says, a search will be best to show up the details. Both of my M59's have been the same, fan only coming on when the engine is running, it's probably controlled by the BSI.
There are 2 types of heater control, one has 4 positions, the other is constantly variable, my '08 has the former while the '04 had the latter, both have aircon. I'm not sure what dictates if it's one or the other, maybe something to do with the year it was made.

[jericlin]

Thanks for response. The M59 heater doesn’t have a resistor pack but is controlled by a pair of MJ11016 NPN Darlington Transistor, 30 A power switching with speed selection via selection of one of four terminals probably to earth via the dash control knob. The permanent live to the motor at 20 or so amps would need to be through a relay controlled be bsi or another “ engine running “ sensor. This relay is the one I need to locate or identify if this helps. Then I can start testing through to find why the fan only switches on when it feels like it.

[cancunia]

Could you wire a bulb or LED to the positive feed, or perhaps run a positive feed direct to the fan motor with the original feed disconnected? That way you'd know if it's the positive feed that's causing problems. I can't remember if the fan has it's own fuse or if it shares a fuse, the handbook should have more info on fuses. If you don't have the handbook, there's one in the 'useful documents' thread at the top of theM59 section.

[jericlin]

Thanks. Will check the handbook for the fuse. As said before currently the fan runs fine BUT I do not turn it off on the heating/vent panel. From past experience if I turn it off it’s pot luck when and if it will next work. If I know what ( a relay ? ) controls live feed to the fan WHEN the engine is running then I have a complete circuit I can check and rectify

[cancunia]

Mine was similar, I left it on low all the time just in case. I think the problem may be the contacts or maybe its a resistance strip behind the dial, I found that tapping the dial with my finger would make it work again.

[jericlin]

Mine was similar, I left it on low all the time just in case. I think the problem may be the contacts or maybe its a resistance strip behind the dial, I found that tapping the dial with my finger would make it work again.

Thanks. Without full knowledge of your " dial " and its interface with selectable circuits to control the heater fan, my berlingo has air con and the " dial " rotates clockwise and anticlockwise around Off position, each position selected connecting the fan motor to earth via the appropriate  control connection to the fan controller module. As the fan speed is controlled by power switching transistors I think there will be no resistors or resistance tracks behind the " dial " but i haven't taken one apart as my first concern is to prove that the live feed is being consistently provided when the engine is running.
Couldn't download handbook on my phone so going to try to on laptop next

[hawaiianblue]

The strips behind the dial aren't normally 'resistance' strips, they're just electrical contacts, they could wear out or become dirty.

There is usually a separate resistor pack often with a heat sink on it near the fan motor. Part number 6450 NV.

Over the years they burn out, sometimes the wiring to it will melt too, if it melts it'll often short out and make the fan run when it shouldn't. That's where I would start looking, I think it'll be easily accessible from the foot well. Start the engine, and switch the fan on and wiggle the wires to the resistor and check for your permanent live there.

[cancunia]

I'd be interested to know what's behind the dial. If there are 4 distinct speeds then I'd expect just contacts, but if it's constantly variable as in my old M59, I'd expect to see a resistance strip. If the motor speed is controlled by Transistors, my limited electronic knowledge suggests to me that the control of the Transistors via the dial is low current. As it happens, I get the same intermittent problems on my newer 4 position control.