Heater Control Fault

[bewickeman1]

I've read all of the relevant posts about heater problems for advice about my heater problem, yet mine seems to be different to all other problems reported ! the car is a 96 vsx turbo ct auto, the heater has the three knobs and does not have a/c, but does have the auto function on the left knob. Basically, the heater stopped working full stop - no intermittent fan switch problems, just no fan at all, all of a sudden, the direction control works obviously (as it's cable driven) but the temp. control also does not work, luckily the system failed with the heater flap open so when i drive above 40mph with the fresh air flap open it creates enough draught to circulate the hot air into the car but if i try to change the temp it does not deviate and the fan does not come on at all - Is there a fuse for this control as i cannot seem to find it or any blown fuses for that matter ? - any suggestions are appreciated ??

[noz]

Hi bewickman1,

Please find attached the wiring diagram for the part of the electrics which is causing your problem. It looks like Fuse 2 or relay 821. Alternatively fuse 3, 5 or relay 848. You'd need to do some searching with a meter to diagnose any further.

Sorry for the file size. I must find out how to reduce it !

Please let us know how you get on.

cheers

noz

[bewickeman1]

Thanks for the quick reply noz, i'll test these circuits tomorrow and let you know - this site really is tremendous and your knowledge is astonishing !
Kind Regards, Andrew (Bewickeman1)

[Little&Large]

Hi
I have a similar but not identical problem.When I bought my car it had the left hand knob bi-passed to a simple on/off switch which either means nothing or full blast.The other 2 knobs perform their function correctly.
Recently the heater started playing up and working intermittently,before finally packing up.However I whacked the top of the dash above the controls and it started working again,it doesn't do it every time(start working again),but it suggests there is a poor connection.I would presume that you have to take at least part of the dash board off to get at it.I am happy with the air on hot and circulate which is adequate to keep warm but no good for defrosting etc.
So from someone who does not know too much-I would say it is possibly a connection!Sorry it wasn't much help!

[xmexclusive]

Hi

Try the 30A fuse in the engine compartment fuse box at the front of the battery and the air filter. This provides all the supply to the heater fan. The fuse contacts and wire connections are prone to corrosion and may fail even if the fuse remains good. The fan can be disconnected and tested with a supply direct from the battery.

Regards

XMexc

[bewickeman1]

A Big Thankyou to XMexclusive ! - as your prognosis was indeed spot-on ! After previously checking the fuse and it looking ok. I removed it under your instructions and found the contacts to be slightly corroded so replaced it and now have a complete heating system that works !!
So to recap - If anyone has a non-aircon heater that has totally stopped working then try the fuse no. 2 located in front of the air filter housing under the bonnet as it is likely to be corroded or burnt, if you have read the owners manual or a repair manual this tells you that the fuse is used for air conditioning - but obviously covers the whole heating system even if it's not air con or climate control on your car !!
Many thanks to Noz and XMexcl and keep up the good work !

Cheers, Bewickeman1.

[nuthallblade]

As a variation on a theme, the auto and 1 - 4 settings on the fan control have gone tits up, but the fan still works on the gale force 9 fan symbol. I have replaced fuse F2 and cleaned the contacts in the fuse holder as best as I can, so before I take the fuse holder off and check the wiring/contacts underneath, is there a secret Citroenesque fuse or relay to check first that is hidden away somewhere?

TIA.

Mike.

[Peter.N.]

Its more likely to be the regulator transistors on the motor itself.

Peter.N.

[nuthallblade]

Many thanks Peter. I've just looked in the help files and it looks like it's one of the easier XM tasks (famous last words!). I had a similar problem with the Xantia and the process seems pretty similar.

Mike.

[xmexclusive]

Hi,

The fan motor has a brown 4 contact plug and a pair of single wires/plug connectors (one red the other black. The brown multi plug is the supply into the assembly from the car. The red and black wires are the power supply to the fan motor after the transistors. All these connectors are on the underside of the fan motor assembly can be reached with taking the fan out of the car. I have found it useful to test that the fan runs insitu with temporary lead putting 12volts on the red and black connectors. If this works ok then disconnect the brown plug and make sure that 12volts is present on this plug (2 of the wires are heavy duty & red and black).

If the fan does not run on the first test then the fan motor is defective.
If the fan runs on the first test and 12v is present on the second test then suspect one or both the transistors.
If 12v is not present on the second test then it is a fuse, fuse contact or wire fault in the supply.

Of the 10 or so fan assemblies I have recovered only one has had defective transistors. If you are down my way and need a servicable one the let me know.

Regards

XMexc

[nuthallblade]

Hi John.
Trust me to have the most unusual fault as the fan runs ok on full blast but not at all when it needs regulating by the transistors. #1 son should be along next week and he is looking at getting the transistors required, or failing that I'll distract his attention and nick his fan unit .

Mike.

[noz]

Hi guys,

The 'working on full speed but not at any other setting' is a classic symptom of transistor module problems. What you may not know is that on the underside of the module pcb there's a relay. When the fan control knob is turned to full speed the signal from the controller is sent to the relay and it pulls in, bypassing the transistors. At full speed the transistors play no part in the circuit. What that does prove is that the fan motor is whole and hearty. This does not mean however that the module is necessarily bust. The problem is more likely in fact to be corroded connectors.

Take out the fan and module as per the self help file. Dismantle and clean up all of the electrical connections. If you have a meter with a diode test function (most moders DVM's have) then test the transistor(s) by checking base-emitter and collector-emitter whilst on diode test. Grease all the connectors and reassemble. 9 times out of 10 this will restore your fan to its fully working condition.

Hope this helps.

Cheers

noz

[xmexclusive]

Hi Noz

Thanks very much, that helps my understanding of fan motor control no end.

Regards

XMexc

[nuthallblade]

Hi Noz.

And me.

Mike.

[nuthallblade]

Very Citroenesque!
Without me doing anything, the fan now works on 3 & 4 as well as full chat, presumably this would point to the relay being ok but one of the transistors being knackered. Or do I still not understand this electrical minefield that passes as a motor car?!!

Yours very confusedly.

Mike.