Monday, 29 February 2016

Electronic Cooling System Control

Cooling Control Unit:

As the Tatra is an air cooled engine, it is fitted with a control box to control if the air intake fan runs or not.
How it is supposed to function is that it monitors the engine temperature and oil temperature, once the engine head temp reaches 150 deg  a voltage is removed from an oil valve that allows oil to drive the cooling fan,  thus if the system fails the fan runs all the time.

There is a light on the dash that tells you the system is working or indicates a fault.
Here is a picture of the said control box,  very industrial looking isn't it.

The fan on my truck was running all the time, however the warning light was not working either,

I started my investigation by checking continuity from the control box to the various sensing elements, there are two temperature sensors on the engine heads, there is an oil temperature sensor, there is a wire to the oil valve for the fan and there is a wire to the warning light.
There is also a ground and a +24v

All of these connections were present at the control box except the 24volt from the ignition, on further investigation i discovered this wire had been taped up inside a loom and never connected. Furthermore there was no bulb in the warning light.

Once i had connected the control box to the 24v feed and put a bulb in the light all was well.  So that's the cooling control working as it should.

The alternator charge light:

This little problem was really easy to fix,  the warning light had broken at the back and the bulb holder had fallen to bits, i checked all the wiring, it will be sorted once i replace the part.