The window screen wiil not clear

Check where the mist is forming.
Does it smell like anti-freeze?

A lite mist on passenger side with loss of coolant you should do a coolant pressure test.

when you turn on defroster on front screen, a/c turns on and directs cold air at window. If your defroster does not work. It may be due to a defrost switch not working.

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Correct.
The ac runs in defrost mode to help dry the air blowing on the windshield. The cabin has too much moisture in the air.
You need fresh outside air and it needs to be dried by the ac to work correctly. So if the cabin air filter is dirty you would not get enough fresh air.

sounds like your fan is either jamned, burnt out or even frozen, you might be lucky and find its just a blown fuse, you'll need to check your fuses box then start investigating if the fan turns freely or not

if you put the air on recirc you might be able to stop cold air blowing in when you are travelling. if you are waiting for a garage to sort out the fault then get a fan powered by the cigarette lighter, air moving over the window should at least keep mist clear even if it doesnt defrost it

It sounds like the heater core is leaking engine coolant into the passengers side compartment. White mist could be steam from the hot coolant? The Heater fan could be damaged, or it is a short. Fill your radiator and take it to the shop or replace the heater core.

Not sure if this is the problem, but the symptom that you describe is consistant with what happens when you get a heater core leak. When the system gets pressureized, you likely have a mist spraying..like a vapor in your heater box. The fan then carries the mist to the cabin and moisture forms inside the car. Usually when this happens, it will be accompanied by an odor of coolant. Also over time, your coolant levels will drop. As the condition worsens, your passenger side floorboard could start getting wet. Good Luck! I hope you find this very helpful!

You have a leaking heater core.

Check the Resistor component in between the wiring and the blower motor. it has a plug and it controls the blowers speed .

there is some mositer in the vents of the car i think there may be a leak letting water in to a vent on your dash fixleak then find the water in the duct work of the car then drain then let it dry

The fan could just be dead. To test the fan apply 12 volts DC directly to the correct wires of the fan. I just replaced a dead fan in a PT Criuser.