Cooling fan stuck on

[James McGrath]

Hello everyone.

I'm having a spot of bother with the Diplomat; the radiator cooling fan seems to be stuck on permanently.

It comes on with the key at position II without even starting the engine.

I've got the two stage fan on the Diplomat as it has air-con and it sounds like it's running at the full speed.

I thought the fan switch might have become unplugged but it looks fine to me.

Any ideas what it could be?

[3cav3]

Is it likely to be the thermistor in the radiator? I had a golf many years ago that used to be the exact opposite i.e the fans wouldn't cut in. As a temporary measure I used to short the connections with a piece of wire, when approaching town traffic.A new thermistor cured it and only cost a few pounds,

[Robsey]

I would say that it is either the thermo switch
or a stuck on relay.

I did update my fuses thread to give relay locations.
You are looking for the stage 2 relay by the sound of it. In the engine bay fuse / relay box.

Relay's exact location depends on model year -
Scroll down to the year you want - relay K25, K26 and K34...

viewtopic.php?f=15&t=4904

[James McGrath]

I think I only have 3 relays in the engine bay fuse box alongside just two big fuses, so that won't be difficult to find.

It's actually got two radiator switches; I'm guessing one for the engine and one for air-con
Could I test the radiator switches with a multimeter? Would the switch show high resistance if it was defective or the other way around?

[Robsey]

If it is a switch, then it should be -
open circuit (infinitely high resistance) when off,

Short Circuit (very low resistance) when on.

If it is a thermal transducer, then it will have a scale of resistances.
These are generic values for coolant and engine temperature sensors for Vauxhalls.
(The table values are very specific, but these are round up / down below within 2 of the table values).

20°c = 2,510 ohms
50°c = 850 ohms
70°c = 445 ohms
80°c = 330 ohms
90° c = 250 ohms
100°c = 185 ohms

So high temperature = low resistance.

[James McGrath]

So in theory, if it is the temperature switch at fault, the fan should switch off if I unplug it as the resistance will go to infinite ohms?

[Robsey]

If the switch is unplugged,
then yes it should kill the fan.

If it does not, then it is probably be the relay.
To confirm this, unplug the relay.

If it still runs, then look for a damaged loom. Possible short to earth.

I think the likely weak spot is the relay...

[James McGrath]

Great stuff, thanks for the help.
I'll confirm when I get home.

[Robsey]

Excellent -
I look forward to seeing what you find.

[James McGrath]

Right, well, I've tried unplugging both radiator temperature switches but this has no effect.

As for the relay, I think I've located the right one.
The fan turns off when I pull it out, but when replaced with an identical one it just turns back on again.

[Robsey]

There are four versions of dual stage fan.
1 for diesel,
2 for air con
And a fourth for X25XE.

All very confusing.
Version 4 is the simplest.

If you have only a couple of relays in the engine bay box, they will both be for the radiator fan.
So if one makes no difference, try playing with the other.

Also - see if you do have fuse 4 in the dash fuse box. Some cars with AC do, some don't.

[James McGrath]

Here are the relays in the engine bay:



It's the bottom right one that seems to control the fan. At least it turns off when I remove it.
The others don't seem to affect it.

[Robsey]

Are the two maxi-fuses okay.?

I know some systems put the fan on if a fuse fails. But this is usually only the stage 1 fan speed.

I can only recommend checking the fuse and relay listings for your model year and engine specification.

I have had a quick look at the 1993 wirh air con.
- there are relays behind the main dash fuse box too.
A right faff to get at / to.

After that, it will be checking wires and connectors - yikes!!

[James McGrath]

I checked the two maxi-fuses yesterday but they were fine.

Today, I decided to run the Tech1 on it to see if there was anything out of the ordinary.
I started the engine but decided to unplug the fan completely as it was annoying me.
I then plugged in the Tech1 and did all the usual tests - Annoyingly, nothing came up.

Feeling a bit depressed at the prospect of having to ferret around for wiring faults, I plugged the fan back in and.... Nothing happened!

I ran the engine for a while to let it get hot enough for the fan to kick in and, sure enough, it came on and cooled the engine down as normal.
It even ran at the correct lower/quieter speed.

So, weirdly, it seems to have fixed itself. At least for now.

[Robsey]

I think you may have unwittingly found the cause.

"Unplugged the fan completely"- what exactly did you unplug?

What ever it was, may have either-

1 - cleaned a dirty terminal...
Or
2 - broken the circuit, which allowed one of the "hidden" relays to unlatch.

Either way, at worst it is a temporary fix.

At best just a niggly happenstance occurance that is now fixed.

[James McGrath]

I unpluged the two pin connector on the fan motor itself.

I had already checked it before. The only difference is that I unpluged it while it was running.

The hidden relays seem to be the most likely suspect.
It seems to have done the trick though whatever it was.