Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
The engine will still have to reach a certain temperature for the radiator fan to come on with the A/C on. Here is a rad fan operation chart. There might not be any problem with it.
Radiator fan operation is control by the Powertrain Control Module (PCM) with inputs from the temperature of the coolant, which is sensed by the coolant temperature sensor, and vehicle speed which is measured by the vehicle speed sensor. The PCM turns on the fan through either the high or low speed fan relay. The PCM provides a ground to the relay's control circuit. The fan relays are located in the Power Distribution Center (PDC) (2). Refer to the label beneath the PDC cover for location of fan relays.Refer to Radiator Fan Operation Chart for fan operation specifications. For fan circuit wiring diagrams, refer to WIRING DIAGRAMS.If the cooling fan is inoperative or a Diagnostic Trouble Code (DTC) related to fan control has been set, refer to the appropriate Powertrain Diagnostic Information for diagnostic procedures.
You will want to check the pressure on a scan tool to see if the PCM is getting the correct A/C pressure, to command the fan on.
So let's see.
The A/c pressure is getting up around 450 PSI, and the PCM knows it.
The PCM is able to command the cooling fan on high, but it doesn't.
The relay is good, (high and low)
Sounds like the PCM