71 convertible heat problem

I have a 71 convertible with a heat problem.  It always seems to be blowing hot air into the car.  I'm wondering if there is something missing that would cause heat from under the hood to blow inside the car.  It makes summertime driving kind of tough.  Any suggestions?  Thanks!  

You need to determine first where exactly this heat is coming from as in heater vent or through the firewall. I'm familiar with early heater boxes but not 71's. Early boxes do not shut off the circulation of hot water, they just reroute outside cool air around the hot heater core. You may have a malfunction of the heater doors that control air through the core. Maybe a control cable has come loose. If the system incorporates a coolant flow shut off inline with the heater hose, it may not be functioning. Manual shutoff valves are sold at auto supplies that can be installed in the heater hoses that can be turned off and on by hand. If no heat can be felt coming out of the heater vents, check the firewall for openings or missing seals/gaskets.  

Most of these era Fords had inline S/O valves for the heater circuit. As Cushman has stated, the valve has either malfunctioned or the controls to it have. If it's a vacum operated valve; put a source of vac to it and make sure it operates, from there ensure that your controlling vacumn source is working correctly (will require the use of vacumn diagrams). If its a manual valve (cable type) same drill; make sure the cable moves and the valve operates correctly.