hi i am new to this forum i just bought my first fiat , its a 2.8 jtd autotrail motorhome 2001 , my problem is the cabin heater fan dont work since the day ive had it , i have replaced the heater resistor and put power directly to the motor that all works and the fuse looks good , what else can it be . is there a relay in the circuit somewhere , and how on earth do you take the 3 speed control knob out of the dash to check if its connected . . please help sick of driving with misty windows .

How it works. The positive voltage is applied to the motor via a relay and fuse when the ignition is on. The negative is applied to the motor via the speed switch, the resistor pack varying the speed. In the high speed position the resistor pack is bypassed.

It should be simple to check that the motor is getting positive volts when the ignition is on and that the motor is getting negative when the switch is on high speed.

I have attached the circuit for the later X250 model but yours should be similar.

rayc said:

How it works. The positive voltage is applied to the motor via a relay and fuse when the ignition is on. The negative is applied to the motor via the speed switch, the resistor pack varying the speed. In the high speed position the resistor pack is bypassed.

It should be simple to check that the motor is getting positive volts when the ignition is on and that the motor is getting negative when the switch is on high speed.

I have attached the circuit for the later X250 model but yours should be similar.

Click to expand...

thank you , so there is a relay in there somewhere . my multi meter is broken so cant check for power to motor yet .but i do know the motor works . have you any idea where the relay would be situated as under the dash there are a few thanks again for that diagram awesome ....

1000000volts said:

thank you , so there is a relay in there somewhere . my multi meter is broken so cant check for power to motor yet .but i do know the motor works . have you any idea where the relay would be situated as under the dash there are a few thanks again for that diagram awesome ....

Click to expand...

On the X250 the relay and fuse that are activated when the ignition is on is in the engine fuse box. I am sorry I am not familiar with your model in any detail.
Photo of the X250 attached for info

thank you , i forgot about those other relays , this should be fun , i think i will test for positive at motor first like you said that will eliminate the mysterious relay and no negative would probably be the control knob its all making sense now lol .. i cant believe how quick i had a reply cheers m8....

Here is another quick check to perform. I too had a non spinning fan and this worked out to be the problem.

That big block of a resistor has a thermo-cut out built into the part. It is obvious as a large cylindrical silver resistor like part bridging the block resistor to one of the contacts. Seen here under the green resistor block;


The easy test is to jumper over the cylinder to both leads on each side shorting the circuit so to speak. This removes the Thermo fuse from the equation. If it works then you just have to replace the thermo fuse or the resistor block which has a new thermo fuse.

cheers , already replaced whole resistor block with new
one today and it still dont work .

Switch also can be the culprit. I have replaced the switch before when all failed and Voalia! all worked again. That switch is a complicated thing to get to never the less to repair. I repaired mine - it worked for a while. So I just went to a breakers and found a better one.

Also these heater systems are notoriously badly engineered. Mine (2001 Ducato 2.8) was recalled for the fuse melting down when the fan is operated on high speed (4) for too long. They replaced the entire fuse array but it still melted down the 25A fuses regularly. I have since rewired the fan with 2mm wires and a independent 30A fuse. Careful on this path, fuses are nothing to play with if you do not know Ohm's theory.

Good luck, Hope it works out one way or another.

Update on my quest to get the fan working , i have checked power to the motor it has negative on all setting and when ignition is off but no positive on any setting ???

It will have positive at the motor whenever the ignition is on. It has nothing to do with the fan speed switch position, that only affects the negative to the motor.

Looks like the relay [if it has one] or fuse in the positive feed is the culprit.

See this previous topic and the response from T14086 [moderator] on page 2. He says "with ignition on? (f55 on dashboard fuse box?). This live from F55 goes straight to heater motor"
https://www.fiatforum.com/ducato/126276-ducato-2003-fan-heater-not-blowing-air-2.html

cheers going stick a bulb on fuse see if thats ok . one last thing if all else fails could i just run a positive to the motor via a switch and still use the speed control .

1000000volts said:

cheers going stick a bulb on fuse see if thats ok . one last thing if all else fails could i just run a positive to the motor via a switch and still use the speed control .

Click to expand...

Yes you could do that. Personally I would fuse it at the original fuse rating i.e F55 if it is the correct fuse.

The cigarette lighter is live all the time even with ignition off i have a little blue lit led USB charger in there at all times looks like an alarm lol.

hmm i am starting to think the person who owned it before me may have messed up some wires when they installed a new radio as its directly below the speed control , haven't tried bulb on fuse yet as i have had a guts full of it today ha ha . bloody Fiats LOL only joking .......

My final comment on this matter , i have hot wired the fan via a 30 amp fuse full blast all the time via a switch under dash,there is no Haynes Manual for this particular model and the information on this common fault is vague to say the least . Great thanks to all the people who have helped me .I tried contacting the Fiat headquarters in Italy Turin , where ever it is ? There is no such place ! , DOES IT ACTUALLY EXIST ? apart from that everything else on her works Perfectly especially as shes 15 years old bless her .

https://en.wikipedia.org/wiki/Turin

BTW, Sorry we couldn't help but if the wiring was bastardized then it is all up to you as only you have eyes on the changes....