HOW TO TEST RADIATOR FAN SPEEDS FROM TRINARY SWITCH (DIESEL CDT/i, 1.8 & KV6 Variants

[Jules]

After several requests from members, thought I'd put it here for reference.
This is a DIY test with No T4 TESTBOOK required !!
The old 4 wire motors have quite a short life and fail between 60 - 80k miles.

Testing LOW SPEED FAN
This test is straight forward and is done with one press of a button!

Set the Aircon to the DEMIST function (this overrides the outside temp even down to -30 Deg C and puts the Ventilation fan on full; this can be reduced manually so you can hear what's going on up front)
Don't confuse the Ventilation/cabin fan with the Cooling fan.
Ventilation fan is behind dash.............cooling fan is behind front bumper!

The cooling fan will operate even if there is no gas in the system, or with the Trinary disconnected, only difference will be the compressor solenoid won't be energised. (via small Relay No7 engine fuse box)
The fan should will come on SLOW speed for 2 speed fans & LOW speed for 3 speed motors (diesel variants)

Then with the Yellow/Grey & black wires shorted the HIGH speed will kick in.

Tests for next speed up from LOW

ie:
3 speed Motors
Tests for Fail Safe MEDUIM SPEED FAN function (compressor protection and for the 106°C and 111°C engine temp range)
Or
Later 2 speed motors.
Tests for Fail Safe HIGH speed (used for extra cooling for compressor & fail safe 112 - 119 Deg for engine)

Also proves whether there is insufficient gas in the Aircon circuit if the fan comes on during the test.

Tools required: Paper clip, or bit of wire or small resistor or even a small 12v bulb!

1.8 & KV6 tests are very similar (wire colours differ but plug pins are the same) but engine has to be running on Petrol versions.
V8 tests differ from this & will follow shortly (wire colours differ and test results

Location of Trinary switch (ALL Engine Variants).
Driver's side bulkhead on small bore HP (high pressure) Aircon pipework.


Wires to short to test HIGH SPEED FAN
Yellow/Grey to Black or two wires opposite eachother furthest apart.


Use a paper clip with flattened ends or a resistor lower than 100 OHMS. After a slight delay the Fan Speed should increase.
(above test with ignition on, engine does not need to be running)





Testing the Aircon A/C compressor solenoid Engine running
The other test you can do if the compressor doesn't seem to be kicking in is is to short the 2 Red/Black wires on the same Trinary plug. (this may prove whether there's any gas in the system or not)

If the compressor now runs, the likely hood is you need to get an A/C specialist to do a leak test & then a re-gas.

Set the Aircon to the demist function (this overides the outside temp) or set the temps to LO Or make sure the inside temp is set 12 Deg C lower than the outside temp.

Fault finding guide for no fan operation

For no Low or High speed check the following.

Check 80amp fuse no 4 in engine compartment.(very rare to fail)

Check the large and small relays in the fan control box (carefully lever 10 clips on the lid to inspect)
Wire breaks have been known between the 2 multi-plugs (behind LH wheel arch liner) and the control box.

Check fan earth CO551 (ring terminal between battery box and inner wing secured by 8mm bolt or measure with meter whether the thick black wires from the control box are in fact earthed)
Check continuity of all wires coming into and leaving the fan control box. Wire breaks and joint breaks can happen in the thick or thin cables. Look for tell tale signs of green copper oxide along the cables to the multi-plugs.

Water ingress may have corroded the copper strands.
If all in order there may be a break in signal lines from ECU to fan control box or on extremely rare occasions the ECU itself could be faulty


Diesel owners:

Control box DIY testing (No T4 required)

To check your fan control box is functioning correctly.

Select demist (ignition ON but engine OFF for diesels)

Get someone to listen at the front grill while you press ECON button every couple of seconds.
The low speed fan relay should be heard clicking.

If it clicks but no fan operation, the motor will have worn out (or see list above)

Within the fan control box lies a small PCB which is a tight push fit on top of the relays. Petrol versions do NOT have this therefore the control boxes are not interchangeable.
The relay PCB receives PWM (pulse width modulated signal from ECU)
The square wave varies the Mark space ratio for the different speeds which then gets converted to DC to switch the appropriate relay coil.
On rare occasions the PCB itself can go faulty.
Sometimes the delicate components don't survive the stresses put on them during the gentle levering process to remove it from the relays.

If all in order and still no fan operation, 99% of the time a replacement kit will solve the fault.
Failing all the above the fault maybe a faulty engine ECU if it’s been flooded by blocked plenum drains.
Email any technical queries to [email protected]




Do not attempt to get Air conditioning functioning until you are satisfied all the cooling fan speeds are working. Compressor damage will occur if insufficient cooling for the condensor & more importantly the engine!


Usual disclaimer applies: You do these tests at your own risk. The club nor myself accept responsibility for errors you make or any consequences arising. Note This is for Diesel variants only