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Discussion Starter · #1 · (Edited)
Clearing up cooling fan issues- resolved

Some time ago, I noticed my JTS cooling fan didn't run on high speed. The reason is my A/C is removed.

Details for micro relay, low speed fan (red, 30 amp, listed as FAN under relay cover:
Terminal 86, small blue wire is normally dead (relay removed). The ECU switches a NEGATIVE current to operate the low speed fan.
Terminal 85 is small red wire. It has a permanent POSITIVE feed energised when ignition is switched on.
Terminal 30 (large white wire) is high current POSITIVE supply.
Terminal 87 (large black wire) is switched by relay. It carries POSITIVE current to the fan speed resistor.

All the above works correctly.

My high speed is inoperative due to no signal from AC pressure switch (beside coolant reservoir).

On the large black 50 amp relay, listed as FAN 1 under the cover I found the following:
Terminal 30, large red/white wire is POSITIVE supply.
Terminal 87, large black wire. This takes positive current directly to the fan motor for high speed.
Terminal 86, small red/green wire is a POSITIVE feed for the relay (ignition on).
Terminal 85, small blue/red wire. Normally dead (relay removed) which gets a NEGATIVE current which is switched on by ECU.

I jumped a negative into the relays on the ECU line (terminal 85). Both low and high speed settings work correctly.

My ECU does not switch on the high speed fan which I know is due to the A/C pressure switch not supplying the ECU with the correct signal as A/C system is depressurised. The multiplug for this switch has 5 wires. They are black, grey, green, yellow and white/grey.

Can someone tell me which wires to bridge to enable cooling fan high speed function?
 

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According to elearn shorting grey to black will energize the fan at high speed. These should be connector pins 6 – grey, and 4 – black; black being earth.

The colour codes in the manual don’t quite match what you have so to check: looking at the connector from the wire side with the release mechanism at the top, pin 4 is bottom right and pin 6 top right.

Note though that the description says the fan will run at high speed if the pressure switch OR the temperature sender command it, so shorting the above pins may not do what you want.
 

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Also note that the descriptions on the relay cover don't always match what the relay under that label actually is...
The small relays have colour coded bases, which helps work out which are which.
 

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Discussion Starter · #4 · (Edited)
Resolved

Looking at A/C pressure switch near coolant tank.
TERMINAL 1: Yellow wire.
Normally earth but goes positive when ignition on.

TERMINAL 2: Green/White wire.
This is negative. It is probably for A/C over-pressure but IDK.

TERMINAL 3:Grey wire. This is negative but goes positive with ignition.

TERMINAL 4: Blanked.

TERMINAL 5: White/grey wire. This is dead but when plugged into a switch with a car with operational A/C, this goes negative. This is the wire which needs to be earthed to restore cooling fan high speed function.

TERMINAL 6: Black wire. Permanent earth.

I checked this on my JTS and a CF3 1.8 with 04 reg.

Thanks guys.
Yes, bridging grey to black will bring on high speed fan- until the battery goes flat.

Yes, the relay multi blocks are coloured. I had to reposition mine correctly prior to this. (I didn't HAVE to but, well, you know...ok, yes, I suppose I had to- if you know what I mean)

Black blocks- fans.
Brown block- fuel pump.
Red block- injection system.
White block- A/C compressor.
 

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I checked for the JTS, all years were the same, but clearly this does not match reality! I think your terminal 2 goes to the acu and that this would normally tell the ecu that the acu wanted the compressor engaged, via the white/grey wire on terminal 5. I’m not familiar with the switch symbol connecting 2 to 5 but presumably it inhibits the pump engagement request from the acu if the pressure is too low or too high. Thus shorting 5 to earth would engage the pump; were it there.

This logic seems to says the car does not need the high speed fan unless the air con is working, which seems odd, but there is a lot of deduction in this and maybe there’s more to it…
 

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Discussion Starter · #6 · (Edited)
@R.T. let me double and triple check the wiring multiplug configuration just so we know I have posted the correct information.
If I've made a mistake, I'll edit the post and state it is edited.

Another bonus of this is that if someone's A/C doesn't work, a simple continuity test of the switch of terminals for white/grey and black wires would reveal whether there is sufficient gas pressure in the A/C system to enable it to function (engage A/C compressor). If these terminals are open circuit, A/C won't engage as you pointed out.

Anyway, as soon as I bridged the wires, I was able to diagnostically run the actuator test for "fan 2" (high speed) whereas before it simply gave me a message stating "function not supported".
 

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Discussion Starter · #7 · (Edited)
ELearn wiring wrong for A/C switch

... colour codes in the manual don’t quite match what you have so to check: looking at the connector from the wire side with the release mechanism at the top, pin 4 is bottom right and pin 6 top right
I've checked again. Looking at connector (wire side- not terminal side) or the switch terminal, with clip at top, both cars were configured:
1 2 3 top row.
4 5 6 bottom row.

As a final point, which I have seen discussed elsewhere, a fault in the high current fan circuit (fan, earth, resistor) will not bring on a fault code because the high current circuit is not connected the the ECU. Fault codes are in the low current input circuit (NCR thermistor or wiring) or low current output circuit (positive supply through fuse, relay or wiring).
 

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Discussion Starter · #8 · (Edited)
In case a cooling fan circuit fault code is logged, note this is a fault in the circuit between the ECU to terminal 85 and/or terminal 86 (of fan relay multiplug) back to the ECU.

The cooling fan high current side (through the resistor) via the fan to earth is not monitored by the ECU.

I measured my JTS and found that voltage drop was not more than 0.1 volts in comparison to battery voltage for each component wire.

I did these tests with relay removed and when testing the ECU trigger line, the engine has to be hot enough for the ECU to activate that circuit. Also note, the low speed uses a negative switched feed and the high speed uses a positive switched feed. This is done so separate ECU drivers are used for each circuit so that in event of ECU driver failure, at least one low current cooling fan circuit should still work.

Finally, if anyone is tempted to simply perform a continuity test, ONLY DO THIS WITH ECU WIRING DISCONNECTED.

Finally, if doing these tests by removing relay with ignition on, removing the relays WILL log fault codes but MIL will NOT be switched on.

The only things to add are actuator tests with diagnostic equipment are helpful and if it is a low speed fault, the speed resistor in the radiator may be the fault.
 
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