The condenser needs to be big enough to condense the high pressure hot gas into a hot liquid. Not only is the surface area too small, the amount of refrigerant it would hold is not sufficent to do the job. You could have the system fully charged and not have any useful cooling.
All A/C systems are designed to have a certain ratio between the size of the evaporator (the cool coil) and the size of condensor (hot coil) and hold a specified amount of refrigerant. That insures efficent operation, and no excessive head pressures
How A/C works:
The condenser is up front of the radiator, and it is supposed to condense the hot gas from the compressor into a hot liquid. The hot liquid goes to the expansion valve located in the tubing next to the firewall. The expansion valve lets the hot liquid expand and become a cold gas. The cold gas goes to the evaporator inside the car where the fan blows on the evaporator exterior. The heat transfer from the air inside the car to the cold gas inside the evaporator causes the A/C to blow cold air. The now cool gas goes to the compressor where it gets compressed again into a hot gas and the process starts all over again. Keep in mind that this is a closed system, and the gas inside the A/C doesn't get out unless there is a leak.
A properly sized radiator, a fan that works like it should and a decent tune will fix any overheating problems. Fix what needs fixing, do it right (that can be expensive) and your overheating, even with a working A/C will be a thing of the past.