Technical Fiat Ducato 2004 fan only works on full

[davidhood999]

Hi, as on the title I have the common fault of the interior fan only working on full. I've bought and fitted a new resistor pack but to no avail. Can anyone tell me where I should focus my attention now please? My Ducato is actually a Rapido motorhome and I not now that I've changed the resistor pack that the LED display on a retro fitted USB charger plug goes out when I select 1, 2, 3, or full on the fan speed selector but then comes back on when the dial is returned to 3, 2, 1 or zero. Can anyone advise please as electrics easily baffle me. Cheers. David.

 

[Anthony489]

Hi David

I attach a copy of the Fan wiring and also the Junction Unit B002 (Connectors, Fuses and Relays) under the dashboard.

The heater blower fan is utterly conventional. Current flows from the Battery B099 through Fuse F01 (50 Amp) then through the contacts of Relay T12. From here it goes through Fuse F55 (30 Amp), wire junction D021, Fan N085 Fan speed switch H081, Resistor pack O030 and Earth point C016. The relay coil is only energised via the Int/A line when the ignition is on but the engine isn't being cranked.


The fan current on full speed is quite hefty, maybe 20 Amps and momentarily more as it starts up. This is reduced at lower speeds by the action of the switched power resistors.

I assume that your USB charger is plugged into either the Cigar lighter or the Accessory socket on the dashboard. It's worth noting that Relay T12 ALSO supplies Fuse F44 and the Accessory socket, whereas the Cigar lighter gets its feed further upstream from Fuse F01, Relay T01 and Fuse F52. Note that handbooks sometimes mix up the allocation of F52 and F44.


My suspicion is that you have a fault in Relay T12 (mounted in B002) or its wiring and connections, which is introducing an unwanted high resistance. With the Fan on full, it's dragging down the voltage at the output of Relay T12 and taking the Accessory socket with it. The first step would be therefore to unplug T12 and check its blades for corrosion, then plug and unplug it a few times. Failing that, it may be that its internal contacts have become worn, so try a new relay as they are relatively cheap.


As is usual with Fiat electrics, these chopped and changed over the years so the diagrams are a guide only !

 

[Communicator]

I am sorry to have to point out that the eLearn diagram for the Heater Fan is one which contains some of the numerous errors contained in eLearn diagrams.

I am attaching my attempt at a correction below. I have modified the diagram connections to the fan speed switch.

Further as David says that his vehicle is a Rapido motorhome, it will probably have air conditioning fitted. A different diagram applies when air conditining is fitted. I will also attach a copy of that diagram, but as it does not apply to my vehicle (no aircon), I have not confirmed supected diagram errors relating to the connections to relays J022, J034, and J041.

On my vehicle, relay T12 enables the Heater Fan, and the Cigarette Lighter, while the adjacent relay T01 only controls the power socket. However eLearn does show two cigarette lighters on the diagram for fusebox B002???


I agree with the suggestion made by Anthony489 of a possible relay fault.
To eliminate this open the LH cab fusebox.
Typically there will be two red relays in adjacent positions.
Remove the LH relay. (T12)

Move the other relay into the socket made vacant.
Switch ON ignition, and test the heater fan.

If a new relay is required be carefull. Do NOT buy one fitted with a diode wired across the coil. (Fiat seem to have ignored the Bosch standard for relay coil connections.)

 

[Womo793]

Hi
I had the same issue with the fan speeds on my van(2000). If you didn't have the the USB issue I would suggest it was the fan speed switch which is causing the fault. I could not completely follow your description of the USB issue, but from the gist of it, it sounds like a bad connection upstream causing a voltage drop, as Anthony489 has described.

The switch can be tested with a multimeter, using the ammended circuit diagram from Communicator, the resistance between the fan motor connection and each of the 1 - 4 position connections should ready zero (or near) when the switch is in the corresponding position. A high resistance reading indicates a faulty switch. Please note that the detents (or clicks) come from the knob mechanism, not the switch, so it is better to test it in situ, so you can be clear what speed you have selected.

The final point from Communicator is very interesting, is this because the coil is wired in reverse?
Regards

 

[Communicator]

Hi
I had the same issue with the fan speeds on my van(2000). If you didn't have the the USB issue I would suggest it was the fan speed switch which is causing the fault. I could not completely follow your description of the USB issue, but from the gist of it, it sounds like a bad connection upstream causing a voltage drop, as Anthony489 has described.

I also have some difficulty with David's description of his USB charger sockets. Are they hard wired, or as Anthony489 suggests plugged into the existing sockets? If currently suggested tests do not give any positive results, perhaps David could rephrase his description. In order to eliminate communication errors,"Spock" like precision is required in such statements.

The final point from Communicator is very interesting, is this because the coil is wired in reverse?

In a word yes. Some years ago I downloaded the attached table of Bosch terminal designations. The table clearly states that 85 is the negative end of a winding. This matches the correct connections for several diode equipped "micro automotive" relays that I have used elsewhere. Fiat eLearn always shows 85 as the positive end of a relay coil, and this is the case where I have checked on my vehicle.

 

[davidhood999]

Hi David

I attach a copy of the Fan wiring and also the Junction Unit B002 (Connectors, Fuses and Relays) under the dashboard.

The heater blower fan is utterly conventional. Current flows from the Battery B099 through Fuse F01 (50 Amp) then through the contacts of Relay T12. From here it goes through Fuse F55 (30 Amp), wire junction D021, Fan N085 Fan speed switch H081, Resistor pack O030 and Earth point C016. The relay coil is only energised via the Int/A line when the ignition is on but the engine isn't being cranked.


The fan current on full speed is quite hefty, maybe 20 Amps and momentarily more as it starts up. This is reduced at lower speeds by the action of the switched power resistors.

I assume that your USB charger is plugged into either the Cigar lighter or the Accessory socket on the dashboard. It's worth noting that Relay T12 ALSO supplies Fuse F44 and the Accessory socket, whereas the Cigar lighter gets its feed further upstream from Fuse F01, Relay T01 and Fuse F52. Note that handbooks sometimes mix up the allocation of F52 and F44.


My suspicion is that you have a fault in Relay T12 (mounted in B002) or its wiring and connections, which is introducing an unwanted high resistance. With the Fan on full, it's dragging down the voltage at the output of Relay T12 and taking the Accessory socket with it. The first step would be therefore to unplug T12 and check its blades for corrosion, then plug and unplug it a few times. Failing that, it may be that its internal contacts have become worn, so try a new relay as they are relatively cheap.


As is usual with Fiat electrics, these chopped and changed over the years so the diagrams are a guide only !

Hi thanks for your reply, I will take a look. Cheers. David.

 

[davidhood999]

I am sorry to have to point out that the eLearn diagram for the Heater Fan is one which contains some of the numerous errors contained in eLearn diagrams.

I am attaching my attempt at a correction below. I have modified the diagram connections to the fan speed switch.

Further as David says that his vehicle is a Rapido motorhome, it will probably have air conditioning fitted. A different diagram applies when air conditining is fitted. I will also attach a copy of that diagram, but as it does not apply to my vehicle (no aircon), I have not confirmed supected diagram errors relating to the connections to relays J022, J034, and J041.

On my vehicle, relay T12 enables the Heater Fan, and the Cigarette Lighter, while the adjacent relay T01 only controls the power socket. However eLearn does show two cigarette lighters on the diagram for fusebox B002???


I agree with the suggestion made by Anthony489 of a possible relay fault.
To eliminate this open the LH cab fusebox.
Typically there will be two red relays in adjacent positions.
Remove the LH relay. (T12)

Move the other relay into the socket made vacant.
Switch ON ignition, and test the heater fan.

If a new relay is required be carefull. Do NOT buy one fitted with a diode wired across the coil. (Fiat seem to have ignored the Bosch standard for relay coil connections.)

Hi, many thanks for your reply, do you know where I'm best getting the correct relay from, or how I'd tell if it's the wrong type before buying? Cheers. David.

 

[Communicator]

David,

Before rushing to buy a relay, please try my simple swap test, as detailed by me in post #3 of this thread, and hence prove that your problem is due to a faulty relay.

To remove the fusebox cover, you should use a Phillips No 2 driver, and please note that the screws are semi captive.

The adjacent relay which I suggest using, only supplies to power socket to the left of the steering column. However on my vehicle the connector had been swapped with that for the cigarette lighter.

Should you actually need a replacement relay, I have incuded a link to an eBay search for the original part. If you are not averse to a used item the those at £2.49 delivered are hard to beat. Scrolling down there is an offer for a new item from China at £8.18 when you include postage.

https://www.ebay.co.uk/sch/i.html?_...leDesc=0&_sop=15&rt=nc&_blrs=recall_filtering