heater doesn't always work

Does the engine warm up completely? I'm wondering about the coolant thermostat being defective and allowing the engine to run too cold. Another thing is that there may be a problem in the heater control module in the dash or that the blend air door actuator is not working. It's also possible that the heater core is plugged or there's a blockage in the lines to or from the heater. You may need a Toyota specialist for some help on this. Here's a directory link for you: http://repairpal.com/toyota-repair-in-college-station-texas