2 speed fan and control box on 3 speed car - Straight swap?
 

Evening all,

I was under the impression that the cooling fan on my ZT diesel could be directly interchanged if the corresponding relay box was fitted at the same time. I've just literally finished swapping the old broken 3 speed fan for a 2 wire, 2 speed fan and 2 speed relay box. I upgraded the resistor at the same time.

The fan I was supplied had the connectors cut off where they plug into the car so I removed these from my old 3 speed fan and soldered to the wiring from the new control box.

I did notice that one of the wires was a different colour, blue on the 2 speed rather than blue/red on the 3.

Once all connected up, I tried to run the fan by turning off ECON mode on the AC but I just seem to get a buzzing from the relay box and nothing from the fan.

Before I go back out there (not tonight!!) and start troubleshooting, could someone please confirm whether directly replacing a 3 speed fan with a 2 speed fan and their matching relay boxes should be a direct plug and play replacement? The pins used on the car's loom are the same and all low/high speed switching is done in the relay box?

Thanks!

is this any help ?
https://the75andztclub.co.uk/forum/s...77#post2755977

macafee2

Thanks macafee2, any info on this is always useful!

I've just been doing some more reading and noticed it mentioned that ALL diesel relay boxes have the PCB. Mine just has 2 relays, but the fan shroud is identical to the 3 speed fan I removed... i.e. it has the lower cut out to fit over the intercooler.

Is this a petrol fan, from a 1.8T perhaps?

Hi Andrew,

What are the markings on the control box lid? A diesel 3 speed should be 'M47' and a diesel 2 speed 'PWM2'.

The diesel fans do not have a connection to the blue wire on the car's loom.

The blue/red wire is essential on all fans. On the diesel it carries the PWM control signal so without it, your motor will not run.

To test the fan, turn on the ignition and press the windscreen demist button.
Yes it should.
Yes.

Andrew, you have an alternative solution. Renew the worn brushes in your 3 speed motor for £22 (check the commutator condition first).

I hope this helps but if you have any further questions please come back to me.

Simon

Hi Simon, thanks for the info. Should both diesel relay boxes (M47 and PWM2) have the PCB inside? My new 2 speed box has 2 relays and no PCB which is making me think it is from 1.8T.

I've never seen a 1.8T fan but am just guessing that as the shroud has the cutout for the intercooler, identical to my diesel 3 speed fan, assuming that the intercooler on the 1.8 is in the same place as the diesel.

I will have another look tonight and go from there. If I do indeed have a petrol 2 speed relay box I will probably refit my 3 speed box and do the 3 speed to 2 speed wiring conversion.

Yes.
It's certainly from a petrol engined car of any cubic capacity.

Simon

Using your existing 3 speed control box you should be able to run the 2 speed fan and resistor.

Can't remember exactly but the Revotec fans that Jules supplies are two wire motors the same as the 2 speed fan motors ;)

IIRC the purple wire is not utilised from the 3 speed control box and it utilised the resistor then on either the Red or grey but not sure on which.

Fitted one just the other week but the customer retained the wiring instructions ;)

Russ

Andrew,

Here is a guide by a club member to rewiring a 3 speed control box for use with an MG Rover 2 speed fan. It's a particularly good solution because it requires the minimum of changes. I hope it's useful to you.

Simon

Simon that link is only if you want to convert the 3 speed motor and box to a 2 speed system.
It's not adding the 2 wire motor to a 3 speed control box which is completely different.
You certainly don't have to do all that within the control box when fitting the Revotecs.
In fact I fitted the last one without even removing the slam panel or shroud ;)
The only things I removed were the bumper and the crash beam.

Russ

Hi Russ,

As I understand it, Andrew is proposing to rewire his 3 speed control box to connect to his purchased 2 speed 2 wire MG Rover motor. Doesn't the link show him what alterations are needed within the 3 speed box to achieve this? For example, he will need to know what to do with the motor purple wire.
That may be so, but I thought Andrew has bought an MGR 2 speed system so we don't need to discuss Revotecs. :} But on the theme of alternative solutions, I think Andrew would be better off renewing the worn brushes and keeping his 3 speed system than embarking on a lot of rewiring.

Simon