Tuesday, May 29, 2012

2003 Ford Taurus: A/C Fan not Coming On Time?

AC blower/heater fan is running and starting up.But its not coming up on required time.

You will notice that it comes up when pressure gets too high like 320psi or 350psi or even more then that.

This is most likely a faulty ac dual pressure switch. If it fails, the fan wont come on at proper time and the compressor wont kick off when pressure gets too high, which 350psi is.

As per wiring diagrams if you see:-----
The  fan operation is controlled from the pcm, when the pcm turns the ac clutch relay on it should also turn on the fan relay but isnt. The fan kicks on when high side pressure reaches more then  300psi , and in this condition  compressor  stays engaged as well as pressure then drops and this is not good for compressor.

The pcm gets 2 signals for fan control - one from the ect sensor and one from the dual pressure switch:---
See the wiring diagram shown below for your help:-----

ford A/C wiring diagram

So if the dual pressure switch is acting up the pcm dose not recieve a signal to trun fans on for normal operation.
If dual pressure switch is not working properly, two things happen - head pressure goes up too high as the pressure switch should cut the compressor off when pressure gets too high and fan doesnt cut on when it should to help keep the pressure lower.

And this explains that the signal to the compressor and the fans is not correct due to the dual pressure switch not functioning correctly which is causing the pressure to rise too high and your fan not to turn on until pressure is at 350.

This details will help.


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