The front air conditioning will only come through the defrost vents. It blows cold air but not through the front vents. The rear air conditioning only blows hot air on the floor. What could be causing this and how do we fix it?

A "mode door" actuator diverts the air to defrost, heat, vents, etc. It is moved by a vacuum motor. Either the vacuum line is off, cracked, etc, the actuator is bad (~$26), or the lever that operates the shaft is bad. Start by checking for a cracked vacuum line

Thank you very much, I will check it out.