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How To Add The "Blue Knob" To The Heater Control Unit

Background Details

As you're probably all aware, temperature knob has a marker on it to indicate the required temperature. Ever had problems trying to see it in the dark? well, now you can with the simple introduction of another LED!


Parts Required - all parts are available from www.maplin.co.uk OR www.ebay.co.uk, but if you buy from Ebay, expect everything in vast quantities! LED's are also available from www.component-shop.co.uk

Tools Required

  • 15W fine soldering Iron & Solder
  • 3.1mm Drill Bit & Drill
  • Wire Cutters
  • Philips Screwdriver
  • File

Parts Required

  • 1 x Blue 3mm LED's
  • 1 x 1k5 (1500 Ohm) Resistor
  • 15cm Black Wire
  • 15cm Red Wire
  • Insulation tape


Step 1

  • Disconnect the Battery!

Step 2

  • Remove all the dash trim. If you don't know how to, look Here
  • Remove the heater controls from the trim, the Control unit is fixed to the center console with 3 screws

Step 3

  • With the control unit removed, remove all the visible screws
  • Slide off the back when the clips are opened. 
  • Make sure you remove the screw which passes through the connector PCB otherwise the board can not slide out.
  • Release the clips either side of the case.
  • With the back off, disconnect the lead that goes to the temperature control.  The connect PCB can now be bent over gently to show the remaining screws.  Take these out.
  • Remove the fan knob, careful to catch the collat.  Undo the center nut.
  • Remove the temp dial/white plastic section (unclip the 2 clips on the back)


Step 4

  • With the temp knob removed, using the 3.1mm drill bit, drill in to the "V" section approximately 10mm from the back of the knob.
  • Be very careful not to drill all the way though!


Step 5

  • Take the LED, and cut the legs so that there approximately 5mm in length.
  • Strip 5mm of outer from each of the two wires
  • Solder the red wire to the positive leg, and the black to the negative leg (has a flat on the base of the LED) Then..
  • File the lip off the bottom of the LED
  • Push the LED into hole in the knob. make sure its a tight fit.






Step 6

  • Feed the 2 wires through the temp dial/white plastic, and then though the bulb holder hole in the main PCB, and the access hole in rear black plastic section of case.
  • Place the knob back onto the unit.

Step 7

  • Take the black wire, and cut it a 5cm from the end and strip the ends by 5mm.
  • Solder the resistor on, and cover the resistor/solder joints in insulation tape
  • Solder onto the PCB as per the picture.

Step 8

  • Carefully route the wires so that they do not get trapped/damaged when you put the rear case back on.
  • Make sure you can rotate the knob though its full range.

Step 9

  • Refit the A/C unit to the dash section
  • Refit the Dash to the car


    Now that all the bits have been done, reassemble the whole lot - and wait for night time! Hopefully you should end up with something similar to this.

    Enjoy you Knob.


If you have any problems, please to not hesitate to Email Me! and I will try to resolve the problem!

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