Why air flow only one side?

check for a faulty climate control module.

It could be your heater core or check your over flow tank for the radiator to see if it is your antifreeze is up to the line marked on the side of tank and check the over flow hose, make sure the clamps are tight.

HVAC Vent Doors under the dash- need to be diagnosed
One is not operating- to switch the air flow
HVAC Vent Door Motor or Vacuum Motor
which ever type you have

You will need to check the air passage on the incoming side of the fan also. Most will check the exhaust side and clear it out, but if the incoming side has obstructions it will not allow air flow either.

Fan speed control resistor block is the usual suspect for this. Quite in-expensive $10 - $20 ?
Easy to change, usually. Generally under the passenger side dash mounted in the air flow comming from fan. Maybe 2 - 3 screws on a block with a few wires, looking like it leads into the air cowling. May be behind glove box.
Do not run fan with new resistor out side of the air flow, it may burn out very quickly without the air blowing on it.

You might wish to check the diverter box to make sure that it's blowing the right air in the right places. Also, check the dash ductwork-they like to split.

Sounds like the coil is freezing up either because of lack of air flow over the coil (dirty) or because of low charge.

bad control swicth or block air flow on driver side

No air flow at all means Fan is not working. Also check damper between freezer and fridge.

check for dirty cab air inlet or "HVAC" filter, or heater core is plugged from debris and air is being restricted and wont blow through. it works like a radiator, air ducts can also be getting stuck.