Maw Solutions Ltd    Henfield, W Sussex    Phone: 01273 493343    Email: info@mawsolutions.com

There are several types of switch, all suitable for controlling either electric fans or electric water pumps (or both).

The first possible choice is manual control. Some older cars only need cooling assistance under particular conditions - traffic jams or very hot summers - and a simple dashboard on/off switch is suitable.  Equally, race cars which only run flat out on the track might want the fan to operate all the time the engine is running, and so will have the fan wired directly into the ignition circuit, with no separate switch at all.

Second possibility is a  simple fan switch which screws in to the radiator (or other suitable location in the cooling system). These switches sense the coolant temperature, and at a predetermined level switch the fan on. They keep it running until the coolant temperature reaches a lower predetermined level, when the fan is switched off and the cycle begins again. These switches are also available with dual temperature ranges, so that two fans can be controlled in cascade mode.   This is the way that fans are controlled in the great majority of modern cars, and if you are simply replacing the original electric fan with a new Davies Craig one, then the old switch will work fine with the new fan. It is simple and reliable, although has the drawback that no adjustment of the switch on / off temperatures is possible.

Although simple fan switches are available in a whole range of different temperatures, it’s better to fit a switch that is variable, ie you can set the switching temperature to suit your engine. Running a petrol engine hotter tends to improve fuel economy, while running cooler improves power output a little.  We sell two types of variable switch - mechanical and electronic.

Mechanical Switches
The Davies Craig range of thermatic fan switches comprises a choice of two mechanical switches, and also an adaptor which gives fitting options.  The most popular switch is the 0401 model, which has a 6mm metal probe on the end of a very thin (around 1mm) capilliary tube, leading back to the separate control unit. The control unit is mounted anywhere conveniently near to the radiator, and the probe is inserted into the end of the top hose. A thin rubber seal ensures no leaks when the hose is clamped down over the capilliary tube. A knob on the control unit allows the switch to be set at any temperature between 40 and 100 degC.

Also available is the 0404 model, which is similar to the 0401 but includes a relay and wiring harness, to enable the fan to be switched on by an external input from the car’s air conditioning system.

And for owners who don’t want the capilliary tube trailing from the end of their top hoses, Davies Craig have recently introduced a sensor adaptor kit, part no.0409. The kit comprises an adaptor tube which is located in the top hose - a 17mm section is removed from the centre of the top hose, and the two trailing hose ends are rejoined using the adaptor tube. The tube has a threaded insert, which by means of the supplied compression fitting accepts and clamps around the switch’s temperature sensor. Both 6mm and 1/4” glands are supplied, together with the necessary hose clips.  If that doesn’t compute, have a look at the 0409 installation instructions and specification (pdf files - click below).

Electronic Switches

Our electronic switches have the benefits of no moving parts, and instant response to coolant temperature changes. They comprise an electronic temperature sensor, which is encapsulated for reliability and protection, with access to a small potentiometer which allows the switching temperature to be varied between 70-120 deg C. The sensor is bonded to an aluminium tube, which fits into the top hose in the same way as Davies Craig’s 0409 kit described above. The tube (overall length 65mm) has swaged ends, allowing a proper water seal when the two halves of the top hose are clamped to it.

Because the inside diameter of top hoses varies from car to car, the switches are available in a choice of tube sizes: 25mm 28mm 32mm 35mm 38mm and 45mm. The electronic part is the same on all switches. They are supplied complete with a 30-amp relay, wiring, hose clamps etc.

We also sell this screw-in version of the switch. It has exactly the same electronic control, but is mounted in a small cylinder with an M22x1.5 threaded end. This switch is a direct variable temperature replacement for simple fan switches (with 22mm threads), or it can be fitted to your engine wherever you can insert a suitable tapped hole.

Note: although suitable for the great majority of vehicles, all of the electronic switches are for negative earth systems only.

Please feel free to phone us on 01273 493343 to discuss any of these switching options.