Car heater problem
January 16, 2018 at 11:02 am #149
blower on picasso stopped working on 1-3 then finally on 4. fuses appear fine. replaced heater resistor unit but no luck. have tested motor – spins ok. meter shows no voltage getting to motor with engine running and heater control on.
I’ve done some research and often a cause is connections failing due to high load and could be related to ignition switch. someone suggested connecting an a 40A in-line fuse between yellow and red ignition wires to get voltage to motor. Should this fix?
January 16, 2018 at 11:02 am #150samParticipant
Don’t know about the rest, but the fuse should be small enough to protect the cable feeding the motor.
Sorry I know little about cars.
January 16, 2018 at 11:03 am #151garyParticipant
Isn’t this normally a resistor failure?
January 16, 2018 at 11:04 am #152tomParticipant
Sounds a lot like a failure in the idiotically designed speed control module.
If 4 slowed down whilst 1-3 were failing I would lean towards a wiring failure. If it stayed at full power then I would lean towards the speed control module.
Most speed control modules have a power input, a power output and a control input. If you bridge the power input and output wires together on the blower module with a bit of wire, does the fan come on? If so you can use a switch wired to the pins on the plug with some crimp spade terminals as an emergency bodge until you can get a new unit. On the connector: Power input is normally at 0V, power output should be at 12V when the control unit is disconnected and the control input is somewhere in between, changing with the temperature knob.
The units typically change the resistance of the ground connection of the fan, hence the counter-intuitive voltages. This is a stupid way of doing speed control designed to bake the transistor to death. Why they don’t PWM drive it is beyond me.
If it is a wiring fault, don’t assume that it’s in the 12V feed – there may be more connectors (typical failure points) in the 0V feed. Measure the resistance from the motor’s connector to 0V at the control unit plug and to the fuse to determine the failed path.
January 16, 2018 at 11:04 am #153
@tom thanks for your detailed response. i actually tried looking for the ‘blower fan controller’ as per http://www.autoinsider.co.uk/problems/problem-10641-citroen-xsara-blower-speed-control-module.php earlier today but couldn’t find it and no reference to one in haynes electrical section..
so ignition hack may not work?
edit: above link not my car so maybe picasso hasn’t got one or do you mean the rotary speed control on the dash?
ps, hope the mouse that took up residence in my car at about the same time had nothing to do with it;)
January 16, 2018 at 1:46 pm #238
Isn’t this normally a resistor failure ?
@gary yes thanks, that video helped me a lot. i think that may have been the initial problem with only blowing on max, but didn’t fix- something else caused total failure.
I then focused on the heater control panel as suggested and measured voltages there- still nothing getting through.
so it had to be the ignition, right?
and it was!! I’ve just connected a wire between red and yellow from ignition at the fusebox and it now blows like a beauty! no more fogged screens. thanks all
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