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I havent driven my c4 since before Christmas but ive been starting it regularly and keeping it snow free. Just started it again but the air con and demister isn't working. Could it be frozen?

  • “Isn’t working”? What exactly does that mean ? Is the Heating, Ventilation, Air Conditioning (HVAC) fan turning on? – zipzit Feb 4 '19 at 0:46
  • The fans at the back are working whereas the front is dead. Controls work and I can hear the directional units working but no air is coming out – P Hinton Feb 4 '19 at 15:32
  • Does the front fan have four different speeds or is it infinitely adjustable? If four speed version I’m thinking the thermal limiter is actuated (and now is an open circuit). The fix for that is to replace the resistor block. – zipzit Feb 4 '19 at 19:40
  • Thanks for that, I think it has more than 4 speeds, just been to my garage and my mechanic got it going, gave it a wacky apparently, its working at the moment but if it's short lived were going to swap out the resistor first before the fan unit. Time will tell, thks for the input. – P Hinton Feb 6 '19 at 13:56
  • Just wanted to let you know you were right, it's the resistor block, its all corroded due to water, new one ordered today, thanks very much. – P Hinton Feb 7 '19 at 19:02
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Comments summarized into an answer:

Further comments indicated that the Heating, Ventilation and Air Conditioning (HVAC) fan was inoperative.

There are two types of HVAC fan control systems.

  • the simple blower resistor system (which generally offers three or four discrete fan speeds)
  • the more expensive infinitely variable system ( which uses Pulsed Width Modulation [PWM] to control fan speeds.) This style of blower controller is pretty robust for the life of the car. Its just a pretty expensive option.

The simple system uses a resistor block which also contains a thermal fuse. One the fuse goes, you have to replace the entire block. This is a great first time do it yourself repair. The part generally runs $10 to $13 USD or so. Generally the block is mounted in the HVAC unit behind the glove box on the passenger side of the instrument panel. You are going to want to purchase a repair manual (Chilton or Haynes) so you know how to remove the kick panels and/ or glove box to get to the resistor block. Remove a wire connection, remove a few screws and replace the resistor.

I suspect that thermal fuse (also called a thermal limiter) is blown.

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