Heater blows cold air

You don't have a control valve. The heat is maintained by a blend air door. It is located near the heater core. Based on its position, you either get heat or AC in the vehicle.

If you are getting no heat, first make sure the coolant level is full. Next, make sure the engine is running at a normal operating temp. If it isn't warming up, replace the thermostat. If that is working properly, do this. Start the engine, let it warm up with the heater on high. Feel both heater core hoses. Both should be hot. If they are, you are getting circulation through the heater core. THus, the blend door isn't working. If only one hose is hot and the other is slightly warm, have the heater core flushed.