"H" - is for "Heater Control Light" By Ian Hopley
For those of you with climate control on elderly 164s, you may have experienced problems with the illumination on the cabin temperature display either not working altogether or working intermittently. This could be a very simple matter to fix so it's worth a try for the sake of 15 minutes work.
First of all, remove the heater control unit. Slide the "J" shaped piece of trim on the edge nearest the steering wheel downwards slightly and then pull it away from the dash. Be gentle with it or you will break the little plastic clips!
This will expose two screws holding the heater control in place. Remove the two screws and the little square plastic clamps that hold the control unit in place and withdraw the unit by pulling the RIGHT hand edge towards you out of the dash. NOTE, be very careful not to crack the plastic trim on the lower, innermost corner of the instrument binnacle as you do so!
As the unit comes out of the dash, it will be stopped by the wiring connector on the back. Squeeze the little plastic lever at one end to release it and then pull the connector off starting with the end that has the little plastic lever.
You can now take the unit somewhere more comfortable! Undo the four self-tapping screws that hold the two halves of the unit together. There are two in each side. Separate the two halves of the unit carefully. They are connected by a short piece of ribbon cable at one edge.
The illumination lights for the cabin temperature display and the clock are both set into the circuit board contained in the half with the switches on it. They can be removed by using a screwdriver in the plastic slot of each one to turn it a quarter of a turn and then pulling them gently out of the board.
The biggest problem is that the solder tracks on the printed circuit board oxidise and electrical contact is lost. A similar thing happens to the contacts on the bulb holder. A squirt of contact cleaner (NOT WD40, as this can dissolve the lacquer on the circuit board!!!) usually sorts this out. Remember to clean the contacts on the bulb too!
If you are in any doubt as to whether or not the bulb works, test it with a 12v battery while it is out of the unit. If it doesn't work, you have a problem because they aren't sold as spares and they don't seem to come out of the holder without breaking. One option I have used in the past is to buy a capless instrument light bulb from Halfords (1.2 watt or maybe even a bit less if you can find one) and CAREFULLY solder the terminals to the two contact patches on the circuit board. Obviously this is pretty drastic and ruins any chance of re-fitting the correct bulb and holder if you should find one but it is a possible way out of the problem!
When you've done whatever was necessary, put it all back together and return it to the car. Re-fitting, as they say, is the reversal of the removal procedure. The only really important thing to be careful with is re-fitting the big connector on the back. One end has a hook on it and this needs to be located first. Then gently press home the connector at the other end (the end with the little plastic lever) until it clicks home.
Once the screws and plastic lamps are fitted, re-fit the "J" shaped piece of trim and re-set the time on the clock. Hold down the middle button and repeatedly press one of the other buttons at the same time to advance the hours or minutes as desired.
Article Content and Photos
by Ian Hopley.
© Ian Hopley / alfisti.co.uk 2003