Cooling fan runs based on AC Hi side line pressure. All operations are controlled via the ECM, i.e. compressor clutch, fan relays, etc...
From FSM wrote:
A/C HIGH PRESSURE SWITCH DESCRIPTION (operation)
The A/C high pressure switch controls both A/C compressor clutch engagement/disengagement, and electric cooling fan operation when equipped with the 2.8L diesel engine.
The A/C high pressure switch controls the electric cooling fan operation by monitoring refrigerant line pressures.
When the A/C discharge line pressure rises above 1900 to 2200 kPa (280 to 320 psi) the fan will turn on*.
The cooling fan will turn off when the A/C discharge line pressure drops to 1600 kPa (235 psi).
The fitting for the A/C high pressure switch on the A/C discharge line is equipped with an O-ring seal and contains a Schrader-type valve, which allows the switch to be serviced (replaced) without discharging the refrigerant system.
If the A/C high pressure switch is faulty or damaged, it must be replaced.
See page 22, section 24 of the 2005 FSM.
*It does not state which fan speed is selected, but I think most believe it is the HIGH speed?
Without a logic flow diagram of the ECM we are left to guess on some matters...
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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited
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