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Old 04-26-2012, 08:08 PM   #1
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Thermister or Switch?

My 87 CRX HF has the typical coolant temperature sensing device in the bottom of the radiator. I have access to three different wiring diagrams each showing this device as a temperature "switch"... meaning it is either electrically open or electrically closed. Problem is my existing temp sensor reads like a thermister. It reads fairly linear... decreasing about 100 ohms per 10 degrees F. (used the stove and a pot of water to test it)
I bought a new temp sensor because my cooling fan turns on and off randomly and I'm searching for the problem... the new one was supposed to be the right one... but it is a "switch" (reading open at room temp).
So - does anyone have some reliable info that we/I can have confidence in?
The attached drawing shows the thermal sensor as a switch. In this circuit it could only be a switch because a variable resistance device in this circuit would only cause the fan relay to chatter.
Anyone?
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Old 04-27-2012, 06:46 AM   #2
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Re: Thermister or Switch?

At what temp does the switch of the new unit close?

I'll check the unit on my 87 civic this weekend and let you know what resistance it reads when cold.
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Old 04-28-2012, 08:14 AM   #3
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Re: Thermister or Switch?

Quote:
Originally Posted by Erik View Post
At what temp does the switch of the new unit close?

I'll check the unit on my 87 civic this weekend and let you know what resistance it reads when cold.
The new unit closes at ~195 and opens again ~180.
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Old 05-01-2012, 05:46 AM   #4
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Re: Thermister or Switch?

I just checked mine- it is definitely open (infinite resistance) when the engine is cold. It sounds like the new "switch" should be the correct part.
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Old 05-01-2012, 06:48 PM   #5
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Re: Thermister or Switch?

I guess I'll put it in... I just hate to cut the harness. The new switch requires a different harness plug. Maybe I'll make an "adapter pigtail" of sorts to test it. Thanks for that Erik!
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