Temp Switch
 

Hi

my cold start on my mfi equipped 911 is not working, I have tested my temp switch the one that is in the breather plate and found that it was reading 24 ohms when cold and switches at 45 deg C but then only reads 39 ohms, I assumed it was faulty because I assumed that it should be a short 0 ohms when cold and open circuit when hot above 45 deg C but I have tested 4 other second hand switches and they are all the same. Does anyone know if my switches are all okay or all faulty?

Thanks in advance.

Regards

John,

Where are you measuring the contact resistance? It sounds like you actually measured the heating coil ... which sounds OK, at 24 Ohms, cold.

To measure the contact resistance you need to measure from Terminal #W to case ground. The heating coil is from Terminal #G to case ground. You have to clean the switches pretty good to see the 'G' and 'W' marks on the bakelite.

Test your spares again, I suggest!

The contacts from Terminal 'W' to ground SHOULD measure 0 - 1 Ohm when the switch is cold, or below 45°C, or 113°F.

Hi warren

thanks for the reply, i was measuring between both the contcts not between each one and ground, I will have a second look, BTW what does the heating coil control?

Kind Regards

John,

The switch is usually called the Thermo-Time Switch, and the heating coil warms up a bi-metallic strip with the moving contact of the break-action switch. After a few seconds the normally-closed contacts open ... if the switch contacts are not welded closed or stuck.

Hi Warren

thanks again for the info, I have now sorted the problem, when I restored the loom I recrimped the temp wires and thinking it was a straight switch I took no notice of which wire I crimped with the large terminal and which one I crimped with the small, I have put these the wrong way round. Job done.

Kind Regards