Roadster Heater Switch
The Roadster heater switch is a weak point in the system and can fail, here is how to fix and prevent it happening
Smart, in their infinite wisdom decided that to change the Roadster heater switch, the dashboard
had to be removed. This was several hours of labour for no reason. Mad dan from TR.n noticed
that the single fixing for the switch was accessible without the dash being removed.
Here is my interpretation of it plus an interesting addition.
What Goes Wrong?
Even though the contact pad on the switch is designed to reduce the possibility of arcing, the gradual step up in power over the contacts can cause a spark. Every time you get a spark you get a small build up of copper oxide that has a higher resistance than the rest of the copper. Over time, the copper oxide builds up so much that the resistance of the switch increases. More power is used to create the connection which, coupled with the higher resistance, causes a lot of heat which damages the tracks, surrounding plastic, wiring and sheathing.
This is usually evident by the build up of a black/brown layer on the
contacts and possibly a burnt connection and/or brown (earth) cable.
You can remove the flap under the steering wheel and remove the polystyrene block...
...to see the switch from underneath.
Removal of the screw can be done with a standard Torx screwdriver then the switch can
be pulled far enough towards the footwell to disconnect it if you need to. Replacing is awkward
but you can get your hand up behind the dash to hold it in place while you replace the screw.
A Torx screwdriver with a magnetic head will make this a lot easier.
If, during the inspection of the switch, you see burning around the white power
connection, it will need replacing. Go to smart and buy a loom repair kit for the heater
switch. This will consist of a new connector and short lengths of cable protruding from it.
Smart part number Q 0015415V001000000 (Blower switch repair kit).
Remove the switch as mentioned in the previous step, disconnect it, check it for faults
and clean it. Cut the old burnt wiring connector off and use crimp connections to join
the new connector to the existing wiring loom.
Refit the switch as before and test.
Cleaning The Switch
Most people will say, if you have to remove the switch to clean it, you may as well replace it.
Not true, you don't have to remove the switch to clean it, just remove the stereo.
Look in the direction of the arrow...
...move the heater selector switch and you will see the contacts
and wiper section of the switch through the service windows.
Grab a can of contact/switch cleaner (not WD40, degreaser etc), put
the straw on and have a little spray straight onto the switch contacts.
Move the switch up and down so the switch can clean itself.
The switch should now work properly as long as the earth cable hasn't burnt through.
Prevention Is Better Than A Cure
Don't wait until you are having problems with the switch before you do anything about it.
Using the cleaner spray can stop the problems in the first place and any stubborn copper oxide
that won't shift can be removed with a PCB cleaning pencil which is an abrasive stick designed
to clean copper tracks. (available from electrical stores, Maplin, eBay etc)
There is nothing stopping you cutting the plastic bar out between the inspection
windows to give you a bit more access for cleaning the contacts in-situ.
Once you have cleaned the tracks up, consider applying some di-electric grease. This is the
grease used on most open contact switches like the headlight stalk switch to stop arcing.
The reason it fails is because, over time, the grease is moved out of the way by the continual
use of the switch. Yearly reapplication should stop this fault ever occurring in the first place.