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ELECTRIC FAN SWITCH???  Rating:  Rating
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 Posted: 08-14-2005 11:30 am
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nvandal
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Here's my question. I'm contemplating putting in an electric fan. My Saab 900s have a temperature switch in the upper radiator hose that operates a cooling fan tied to the air conditioning system. The manual says it opens ( operates ) at 239 degrees F. Is this switch operating at an OK temp for the Jensen? It would be an easy install and at an optimum location as far as I can see. I would also install a manual overide switch as well.

My assumption is that anti-freeze raises the boiling point of water. Am I correct?

Thanks,

Norm Vandal

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 Posted: 08-14-2005 06:49 pm
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Mark Rosenbaum
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Yes, antifreeze added to water will raise the boiling point, the increase depending on the amount of antifreeze present.

239^F is pretty close to the boiling point of a 50/50 antifreeze/water mix, so the temp switch you refer to is probably intended to disable the air conditioner when the engine gets too hot.  If your Saab were carbureted rather than fuel injected, I'd want the disable temperature about 20^F lower.

For switching an electric fan that's intended to cool the radiator, you usually want a switch that will turn the fan off about 5^F-10^F above the nominal operating point of the thermostat, and turn the fan on some 10^F above that.  Only the turn-off temperature is of any real importance, so there should be a wide assortment of suitable switches.  If you can find a short length of brass or copper pipe of the right diameter, it should be easy to make an in-line mount for almost any switch design.

There are several ways of arranging a manual switch, each with advantages and drawbacks.  My choice would be to use a good reliable solid-state switch and fan controller.  Properly done, the least reliable part would then be the fan itself.

 

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 Posted: 08-15-2005 05:40 pm
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StabnSteer
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Mark is right - the switch on the Saab that is in the upper hose on the cooling system of the Saab is designed to kill the AC when things get too warm. Thus, it should have continuity all the time, unless things get too hot...so if using this, your fans will be on all the time, unless things get too hot, at which point they'll turn off! :o) Just incidentally, the Saab thermoswitch for the fans is located on the driver's side of the radiator for classic 900's...

There are any number of aftermarket thermoswitches you can use for running electric fans. Your local auto parts store will carry a few options with different kinds of temperature probes and different temperature ranges (some are even adjustable).

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