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1995 Astra fan always on & confusion over fan switches

1995 Astra fan always on & confusion over fan switches

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gregh101

Original Poster:

5 posts

Tuesday 12th September
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Hi all. Long time browser, first time poster. This forum has helped me out several times in the past so thanks to those that are so generous with their time.

I am currently visiting my father and his car Opel Astra Estate 1.6i multi point injection, with aircon) has a few issues which I am trying to work through. I have the Haynes manual, but there is one detail I am a little confused about and no amount of reading or research has quite yielded the answer.

Fan comes on all the time (it's been like this for ages, but I think that if he has trouble starting then sorting this out can only help so it's not drawing massive current all the time)

There is talk about 2 pin and 3 pin versions of the fan switch. On this car however there are 2 switches on the same radiator. On the right hand flange there is one near the top with an oval 2-pin connector in black , and one near the bottom with a large round blue 3 pin connector.

My understanding is that the bottom one is a dual temperature switch which runs the fan through a resistor. However I have seen mention that even this switch with the round connector has a 2 pin and 3 pin version.
The one on the radiator right now is showing open circuit when cold between 2 of the pins, and this might be an indicator that it is indeed faulty.

The top one is a mystery to me. I bought a replacement when I thought that this was THE only fan switch (didn't see the other one lower down initially, but then I wasn't looking after I found the top one, haha). The replacement I got is a "euromann thermoswitch for radiator fan FS4362", the guy in the parts place found it based on a sample but what is that for? I also saw some talk about there being N/C and N/O versions of that switch, so I am wondering if anyone can shed light on what they are actually for and whether all of this confusion around 2pin vs 3pin and NC vs NO is real or just the result of noise from too many google searches smile ?

There is another fan on the other side of the consensor, but surely that is controlled by the aircon system and not the second switch?

Cheers,
Greg


robbocop33

505 posts

28 months

Tuesday 12th September
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I have no idea about your particular car, but i had a similar problem on a rover 75 1.8 turbo..
You mention a resistor for one of your switches on the rad. Is this resistor seperate/replaceable?
It's maybe in no way related but my fan was just going on and off regularly, an uprated resistor was available for mine, and was a known weak point, problem was sorted!
Sorry in advance if it ends up being unrelated to your problem! ;-)

gregh101

Original Poster:

5 posts

Wednesday 13th September
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Thanks for the response. I haven't actually located the resistor, I just read about it on another forum! It seems there are several configurations and I am trying to figure out what the 2 switched do as well as what the 2 sensors do. Haynes is helpful but only up to a point and it's not clear to me. The wiring diagrams will probably help but I am finding them hard to read and there are so many variants that I am hoping for some wisdom from an Astra buff.


Mr2Mike

17,497 posts

176 months

Friday 15th September
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If a three pin switch has been fitted when the car should have a two pin switch then it will make the fan run all the time. The number of wires going to the thermo-switch connector is not an indication of the number of pins the switch should have!

Just to be clear I'm talking about the thermo-switch with the large round connector, which is available in two and three pin versions.

Edited by Mr2Mike on Friday 15th September 12:07

gregh101

Original Poster:

5 posts

Monday 18th September
quotequote all
Mr2Mike said:
If a three pin switch has been fitted when the car should have a two pin switch then it will make the fan run all the time. The number of wires going to the thermo-switch connector is not an indication of the number of pins the switch should have!

Just to be clear I'm talking about the thermo-switch with the large round connector, which is available in two and three pin versions.

Edited by Mr2Mike on Friday 15th September 12:07
Thanks for this response. The switch that I replaced had 3 pins in it, but I can't say for use if it was maybe replaced before. My father says that the fan has been coming on all the time for as long as he can remember. I guess it might be worth trying out the 2 pin version, but is there any way of testing which it should be using? I am no longer there but maybe I can check it out the next time I visit.


Thanks,.
Greg
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Mr2Mike

17,497 posts

176 months

Monday 18th September
quotequote all
Does the car have aircon? I may be way off, but ISTR that the cars with aircon use the aircon fan as part of the two stage radiator cooling instead of having a resistor and a two pole thermo-switch.

gregh101

Original Poster:

5 posts

Monday 18th September
quotequote all
Mr2Mike said:
Does the car have aircon? I may be way off, but ISTR that the cars with aircon use the aircon fan as part of the two stage radiator cooling instead of having a resistor and a two pole thermo-switch.
Yes it does have aircon and there is a condensor fan on the front of the condensor. The aircon hasn't worked for some, and I didn't even check to see if the condensor fan was running or not. The main Rad fan comes on full blast as soon as the ignition is on, and it's quite loud. This is what the original looks like- if it is actually the original that is.


One of the guys in the parts place did say something about the one switch that I bought actually being listed as for the aircon- even though it fits in the radiator. I found it all a bit confusing which is one of the reasons I started this thread smile. I couldn't quite understand why there are 2 switches in the radiator anyway. It makes more sense to me though if the 2 switches are actually for the 2 stage cooling, so one drives the radiator fan and the other drives the condensor fan- and then it is logical that the round switch in this system is meant to be a 2-wire job.

I guess it also means that they should have different switching temperatures.

This is what the other one looks like :




Edited by gregh101 on Monday 18th September 16:32

Mr2Mike

17,497 posts

176 months

Monday 18th September
quotequote all
Did a bit of digging rather then relying on my failing memory.

MK3 Astra wiring diagrams.

If you look at page 12.52 you will see the horribly complex aircon/cooling fan control circuit. S29 and S128 are the two radiator switches.

The two pin switch S29 I think is the low temperature stage, and appears to connect both cooling fan motors in series, making them run slowly.

S128 has two sections, a normally closed and a normally open, with a common ground. When the temperature gets high enough the normally open switch will close, and the full battery voltage will be sent to fan M4. If the coolant temperature gets higher still, the normally closed section will open and this disables the compressor clutch to reduce the heat load.

This NO/NC switch seems much less common then the NO/NO switch which is used with a resistor to provide two speeds.

You have the fan on all the time end the aircon is not working. The aircon could be low on gas, but perhaps this switch is responsible for both problems. I'd break out the multimeter and see if you actually do have a normally open and a normally closed circuit on your switch. If so, have they been wired up backwards somehow?

Edited by Mr2Mike on Tuesday 19th September 10:23

gregh101

Original Poster:

5 posts

Tuesday 19th September
quotequote all
Thanks for the detailed response; this is really helpful. I was hoping to just replace a switch or 2 and resolve the problem, but I guess it's just not going to be as simple as that, however you have answered the question I came here with, which is what the 2 switches are all about!

When I took the old switch out I tested and it seemed that I had one open and one closed switch when cool. I took that to possibly mean it was faulty, but it does seem to indicate that NO/NC was in fact the case. Unfortunately I didn't test the new switch.

The aircon hasn't worked for a while. One of my mates who works for a car aircon manufacturer said that the pressure switch can sometimes also cause the radiator fan to come on all the time. That was a non car-specific comment and I pointed out that there is a separate condenser fan; but there might still be something in that. A closer look at the wiring diagram might reveal.

It seems that next time I visit I will probably need to have another look with multi-meter and wiring diagram in hand, but for now I can't really do anything further as I am no longer anywhere near the car.

Thanks so much for the really valuable feedback.

Cheers,
Greg