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Discussion Starter · #1 ·
Hi,

Bought a new radiator fan switch for a 1994 Alfa 164 24v and decided to test it before fitting.

Popped it into a saucepan with almost boiling and then boiling water and put a multimeter across the connectors, various combinations of pairs of the red, white and black wires. Couldn't find anything except an open circuit. Thing is, I did the same with the old one and got exactly the same results.

What am I missing or do I have two faulty switches?
 

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Discussion Starter · #2 ·
Another thought is it might need to be left in the hot water for longer, to let the heat soak through to the sensor part in the plastic. Guess these are designed for gradually increasing temperatures as engines do the same.
 

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Couldn't find anything except an open circuit. Thing is, I did the same with the old one and got exactly the same results. What am I missing or do I have two faulty switches?
I don't think you're missing anything. When I bought a new switch several years ago, I did the same test to understand which pin did what. Mine behaved as you'd expect: one pin was the common, the second connected to the common pin at X degrees, and the third connected to the common pin at X+ degrees. No heat soak was required.
 

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Discussion Starter · #4 ·
I don't think you're missing anything. When I bought a new switch several years ago, I did the same test to understand which pin did what. Mine behaved as you'd expect: one pin was the common, the second connected to the common pin at X degrees, and the third connected to the common pin at X+ degrees. No heat soak was required.
Thanks Alfajay.

That's actually a bit concerning. How did you heat yours up? I put boiling water from the kettle in a saucepan to at least try and get some connection.
 

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If you have OEM Alfa thermal switch black is ground, white is low speed and red is high speed. white hooks to brown, black to black and red to brown-white wire.

Black meter wire to black and red meter wire to white and bring water temp up slowly on stove with switch in water. Meter should show continuity about 198F (93) and then switch red meter lead to red wire and get continuity again about 206F.(97C)
 

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Discussion Starter · #6 ·
Thanks, Steve.

Just put both new and old into thick-based saucepan and gradually brought it to boil.

Interestingly, while the low and high circuits on both triggered at the same temperature points the old one was showing a resistance of around 3k ohms. Not sure if just internal aging due to slight oxidisation on connector but at least have confidence now to install the new item.

All the best :)
 

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How did you heat yours up? I put boiling water from the kettle in a saucepan to at least try and get some connection.
I don't remember in detail. Your procedure ("put boiling water from the kettle in a saucepan") sounds like a good start, but even if the water leaving the kettle was at 212F, it would cool in the process of heating the saucepan and switch. So perhaps your new switch never got hot enough to trigger.

Try putting the saucepan/switch/warm water on a burner to heat it up further - I'd want the water to be boiling before deciding that the new switch was DOA.
 

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Discussion Starter · #9 ·
Worth noting:
the replacement fan switch I bought had the wrong connectors so had to solder on the connector from the original. When cutting the black/common wire near the old switch I found the copper had gone black. Had to cut it back about 10cm to get to good copper - then add an extra length of wire to make up for the loss. The red and white wires were fine.

The blackened copper wire on the, er, black wire could be pointers to heat generation from the resistance inside the old switch. The resistance could also have led to slower fan speeds and less cooling, hence the tendancy to run too hot in traffic.

If your car has the original fan switch, can run too hot and is also some 20 years old, may just be worth chucking in a new one. BTW, took off the radiator top bracket/plate to gain enough access to fit the new switch.

Thanks again to everyone for their help :)
 

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The blackened copper wire on the, er, black wire could be pointers to heat generation from the resistance inside the old switch. The resistance could also have led to slower fan speeds and less cooling, hence the tendancy to run too hot in traffic.
I don't agree:

- If the switch contacts have oxidized and that has increased their resistance, then the wire would carry less current - not more. So I don't think your wire has over-heated due to high current. Perhaps the front exhaust header heated the wire enough to melt some of the black insulation onto the copper. Or it is just oxidized.

- The wires from the radiator switch just operate the fan relays - not the fan motor. Given enough resistance, the relay might not receive enough power to trip, which would result in the fan not coming on. But a relay is a binary device: fully off or fully on. As long as there is enough current to turn on the relay, it will deliver full power to the fan motor. Less current to the relay doesn't mean less current to the fan motor.

- If you still don't believe me, consider this: The two sentences in your quote above are essentially saying that the switch wires carry so much current that they are burning up, but so little current that they are slowing down the fan. Seems contradictory.
 
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