What type of climate control system do you have on this vehicle? Is it electronic(digital display) or is it a manual system with knobs to set the controls?
On the cooling fan have you checked for any trouble codes in the EEC?
Has there been aything wired into the system or is everything totally stock?
I am at the shop now but I will carry the shop manual and wiring diagrams home with me and check back later.
Ok the problem with your heating and cooling fan is the primary cooling fan. It is controlled by the Integrated Controller Module located in the RH front of the engine compartment, right near the EEC self test adapter at the front of the strut tower.
This houses all of your relays,Primary fan,secondary fan,ECF relay, Fuel pump, and AC clutch.
Now how this works is power is supplied on pins 3 and 4(Y wires) to the relay. Ground to the coil side of the relay is provided on pin 17(PK wire). When this wire is grounded by the PCM or by the fan control ac pressure switch this energizes the coil which then creates a magnetic field which then pulls the switch side of the relay closed. Now power will flow thru the switch side of the relay and leave the controller on pins 6 and 7(BR/O wires) and goes to the primary fan. Now get a 12V test light and make sure you have voltage to the Y wires. If that is ok then check the BR/O wires with AC on. If you have power here then go to the fan and make sure it is getting all the way there on that wire. If you have it at the fan then hook you test light to the positive battery cable and then check the BK wire at the fan and make sure it lights to prove out the ground.If it does then your fan is bad.
Now if you do not have power on the BR/O wire check the PK wire at the controller with your test light hooked to battery positive and then turn on the AC and see if it lights to prove out the ground on the coil side of the relay. If you have it here and do not have power on the BR/O then the relay is bad and the controller would have to be replaced.
Now on the problem with your ac blowing thru the defroster under load or boost. Defroster is the default postion for no vacuum. Of course under boost you have no vacuum however you have a vacuum reservior located in the right fender well. I suspect either you have a leak at the reservior or in the vacuum lines from it. I can not remember for sure but the picture in the shop manual it appears you will have to remove the right front wheel and drop the plastic liner down and it should be behind this. Check it good for a vacuum leak and trace the vacuum lines from it,one should go to the intake manifold and the other should go thru the firewall near the heater core hoses.