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Old 05-29-2008, 07:42 AM
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Thermal switch for electric fan not switching on

I bought a thermal switch from summit (on 200, off 185) for an electric cooling fan on my SBC. I have the switch mounted in the intake manifold, and a temp gauge sending unit in my drivers side head. The gauge has been reading up to 215, and the fans won't kick on. I've just been flipping the override switch at that point. The thermal switch has a good ground connection. Any thoughts are appreciated.

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Old 05-29-2008, 08:18 AM
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There's usually a temp difference between head & manifoldmount locations. I wouldn't think 15* though. Try mounting switch in the head and see if it works. If not may be bad switch.
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Old 05-29-2008, 08:45 AM
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If the threading is the same on both the switch & the sensor, you might try swapping their locations just for testing.
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Old 05-29-2008, 09:29 AM
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If you end up removing the switch from the intake, you can always test the switch in a pan of water on the stove, with your wife's meat/candy thermometer. hook up the switch on your multimeter set to test for short/resistance/ground. and boil the water while frequently checking the thermometer for temp, once you reach the temp the switch should turn on, hook the multimeter across the contacts and put the sender in the hot water(carefully!!) if it's functioning properly, it will show on the multimeter! The only big caution here is not that you can be scalded by the hot water or switch, but that you can become the cause of yet another fight between you and the 'ol lady for using her kitchen again for your cars!!
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Old 05-29-2008, 09:53 AM
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Ol' lady in the kitchen? right! If only she spent a minute in the kitchen, for every hour I was in the garage...

I was thinkin about the heated water idea. What should I be checking for to see if it works?
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Old 05-29-2008, 10:04 AM
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I have the same switch. That does'nt work. $30 down the drain!
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Old 05-29-2008, 10:42 AM
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upstand2 did you come up with a solution? I feel the frustration.
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Old 05-29-2008, 11:09 AM
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Quote:
Originally Posted by SSedan64
There's usually a temp difference between head & manifold mount locations. Try mounting switch in the head and see if it works. If not may be bad switch.
There can be about 20 degrees difference in the readings from the intake manifold location and the head location. This is due to the close proximity of the sending unit to the exhaust when installed in the head.

The fan switch is usually installed in the drivers side cylinder head. The temp sending unit is usually installed in the intake manifold.
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Old 05-29-2008, 11:39 AM
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Quote:
Originally Posted by Cousin_Joe
Ol' lady in the kitchen? right! If only she spent a minute in the kitchen, for every hour I was in the garage...

I was thinkin about the heated water idea. What should I be checking for to see if it works?
You want to see if the switch triggers at the high and low temps. (the switch will open and close the circut) :low tech definition-when the temp reaches the 200 degree mark the multitester set to impedance will spike.
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Old 05-29-2008, 06:08 PM
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Quote:
Originally Posted by streetrodderbn
You want to see if the switch triggers at the high and low temps. (the switch will open and close the circut) :low tech definition-when the temp reaches the 200 degree mark the multitester set to impedance will spike.
I believe he means set to "OHMS".

Impedance is a variation of current flow produce by electrical or magnetic flux.
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Old 05-29-2008, 06:56 PM
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Well Mine got to 230 without turning on.
My solution that day was grounding the fans on the radiator bracket.
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