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

[sytneraudi10]

The diesel does not really get hot enough to use thr cooling fan.

On the three speed the low speed works the whole time the air con is on. It shouldnt pulse.

The later two speed should work on the slow speed the whole time air con is on.

Ive yet to see one fail on high speed as its very rarely on high speed long enough to burn it out.

[T-Cut]

Originally Posted by kael

My 2002 CDT has clocked 170000km and the 3 speed fan is still working fine at LOW speed (demist check), I mostly have ECON on instead of AUTO.
But when exactly are these 3 speeds used in real live situations? How to observe them?

In the diesel, the coolant temperature tripping points are:
105°C Low speed on. Off at 100°C
111°C Medium speed on. Off at 106°C
119°C High speed on. Off at 112°C

Needless to say, these events are extremely rare. Most diesels never trip the cooling fan, but they will under the right circumstances.

TC

[SD1too]

Originally Posted by kael

Intresting to read how to test: ....
HIGH speed (demist on and then bridge trinary connector)

I've never heard of this before, and I'm not sure that it's correct because electrically it's the same condition as medium speed only. Have you verified it on your own car Kurt?

But when exactly are these 3 speeds used in real live situations? How to observe them?

With a diesel you will only notice the fan running in connection with the air conditioning. Slow speed should be active when 'auto' is selected (with a few unpredictable exceptions) and medium speed when the system is working hard in hot ambient temperatures.

If I understood right the trinary is aswell a temp switch as a pressure switch?

No, it has three pressure switches. It does not react to refrigerant temperature.

Does 'tri' stand for triple action?

It means that there are three switches in the same casing.

Since I bought the car new I Always found that the always-on-fan is kinda annyoing and overkill when riding at high speed.

I'm surprised that you can hear the slow fan when travelling at high speed.

Finally Kurt, there's no doubt that your controlled use of the 'auto' button has extended the life of your motor brushes, but don't forget to use it about once a month all the year round to keep the system in good order and prevent refrigerant gas loss through shrinking seals.

Thanks for sharing your experience with us.

Simon

[SD1too]

Originally Posted by T-Cut

In the diesel, the coolant temperature tripping points are:
105°C Low speed on. Off at 100°C
111°C Medium speed on. Off at 106°C
119°C High speed on. Off at 112°C

These figures come from one section of MG Rover's official manual. However, elsewhere in the same publication the company gives completely different data for the diesel:

Low speed on at 100°C, off at 98°C
Medium speed on at 106°C, off at 102°C
High speed on at 112°C*, off at 110°C

* In yet another part of the document a figure of 119°C is given!

The whole thing's inconclusive and rather academic with the diesel since, as has been said, most owners seem to struggle to increase the coolant temperature rather than decrease it!

Simon

[T-Cut]

I quoted from an old thread by Jules. It's near enough to answer the question and he'll never know the difference.

TC

[kael]

Not yet tested but I understood this from Jules' initial thread:
First he explained to:

Tests for next speed up from LOW

Where you need to bridge the conector and have MEDIUM speed on the 3speed motor.
Then on Testing LOW Speed with activating the Demist button:

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.

I understood the combination of both gives HIGH? Maybe I read this wrong and HIGH speed testing is not possible on 3 speed fans?

Trinary:

No, it has three pressure switches. It does not react to refrigerant temperature

three? I thought 2 since there are only 2 pair of contacts? 1contact for low (normal) pressure and 1contact for high pressure (airco working on full load). What would be the third possible be for?

I can't hear the low speed fan when riding 'fast' but sometime I do when drivin' slow, in city centers, manoeuvres,... or when stopping at a crosswalk and you see them watching to you car 'what is this noise...'

I'm wondering if it is advisable (or done before) to change the circuit to be temp controlled = no LOW speed fan until it is necessary? That would give less noise and less worn brushes. Why do you need a fan on a steady ride on an open road? When there is no riding wind, then of course the fan needs to take over.

Thanks for the tip on montly use, sometimes I do tend to forget.

[SD1too]

Hi Kurt, I'll try to answer your points:

Originally Posted by kael

I understood the combination of both gives HIGH?

No, it doesn't. The 'demist' button turns on the air conditioning and so the radiator fan runs continuously at slow speed only. The motor increases speed to medium when the refrigerant pressure rises. This is detected by one of the trinary switches. In order to test the medium speed, you have to have the fan running at slow speed to begin with. So the combination of 'demist' (slow speed running) + trinary switch (medium speed request) = medium speed, not high.

Maybe I read this wrong and HIGH speed testing is not possible on 3 speed fans?

It is possible, but involves dismantling so is not really practical.

Trinary: three? I thought 2 since there are only 2 pair of contacts? What would be the third possible be for?

The low and high pressure switches are in series, so just one pair of contacts. These control the compressor clutch.
The medium pressure switch accounts for the other pair of contacts. This tells the ECM to activate a faster radiator fan speed.

I'm wondering if it is advisable (or done before) to change the circuit to be temp controlled = no LOW speed fan until it is necessary?

That is exactly what happens as far as coolant temperature is concerned. It is temperature controlled.

Why do you need a fan on a steady ride on an open road? When there is no riding wind, then of course the fan needs to take over.

You are correct. When the air conditioning is operating however the condenser needs to be cooled continuously. When the car is moving slowly, or is stationary, it needs fan assistance for this purpose. MG Rover could have devised a switching system linked to road speed, but I imagine that they decided it would be simpler and cheaper to run the fan motor continuously instead to ensure that the air con. output was reliably cold.

Simon

[kael]

OK, that's clear so far.
I did a test on mine CDT 3speed fan, when I put on Demist, SLOW speed comes on, when I then overbridge the trinary contact, MEDIUM speed kicks in, so everything looks OK on my 170000km car.

[SD1too]

It certainly does Kurt, and it shows that a high mileage car is often a very good one to own.

Simon

[Zebra]

Hello, I've got a 2002 diesel tourer and the aircon. hasn't worked for years; I've been meaning to sort it for ages. Following the instructions earlier in this thread, I've found that the fan doesn't work at all. I suspect that it conked out ages ago and so I've overheated the coolant and now I've no coolant left. The condenser looks surprisingly healthy though. Would the general advice be to fit a new fan and then take it somewhere to have it leak tested and re gassed? Could I have knackered the compressor by letting it overheat though? I wish I'd read these threads whilst it was starting to break down!
Thanks, in advance for anyone's advice.