Question about 2003 Mercury Grand Marquis
Re: "fan goes not come when you turn on the a/c also".
If fan DOES NOT turn on when AC is on. Test the fan motor to see if it is working, If there is voltage to fan and fan does not work, then fan motor is gone. If there is no voltage, replace ECT sensor. Test also the engine cooling fan module. This is not a computer, but simply the an switch/adapter connected to the cooling fan, with connectors for low and high speed.
If fan DOES turns on when AC is on. That happens when the fault is either thermostat or the fan control module (a simple device connected to PCM). This system is computer controlled. When the AC is ON, the PCM will use the input from the AC and this can override ECT sensor.
Replace the ECT sensor first.
Here diagrams :
Posted on May 20, 2011
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Posted on Jan 02, 2017
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