Question about 1990 Mazda MX-5

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1990 miata cooling fan and a/c fan

My cooling fan only comes on when the airconditioner is on , and not the a/c fan. the car overheats because the cooling fan does not come on. i already tried testing both fans directly and the both work. a mechanic looked at it and said it was not grounded somewhere. i am trying to get the fans working correctly and get the a/c working also. Help!

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  • Steve Allison
    Steve Allison May 11, 2010

    Has anyone checked the connections to, and the function of the main fan's thermostat? These aren't the most reliable devices.

    A low-cost multimeter would allow you to check for a missing ground pretty quickly if you don't mind getting grubby from the efforts.

    Best would be removing the thermostat and testing it in hot water with a thermometer or just replacing it but either would require the draining of coolant.

    Thermostats are typically located on the bottom tank of the radiator, are cylindrical in shape, ~ 1" (2.5 cm) in diameter, and either one or two wires potted into the end of the housing.

    Checking them in hot water whould show them operating and producing a short (low resistance) path once they are above their operating temperature.

    I don't see how a missing ground could cause the AC fan to operate in place of the cooling fan unless (VERY unlikely) connections have been swapped since in that case, the cooling fan would run with the AC turned on.

    I think Mazda is bright enough to use connectors that are not interchangeable.



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A multimeter is good but can give you a false reading . i would check with a test light first

Posted on Jun 23, 2008

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Your problem is nothing to do with electrics, it's your thermostat.

What's happening is that the thermostat isn't registering that the radiator is hot and so doesn't open the value to the top hose. The fans will work only when triggered by this sensor. That's why when you switch on your air con both fan work fine. As a double check you'll find that the top hose is hot but the bottom hose is cold, they should be the same temperature. Just be careful when reaching the bottom hose as it's hard to get to. Thermostats are only £12 from Halfords c/w gasket.


Posted on Sep 01, 2008


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