Heater blows cold air on 1999 Ford Explorer

Heater blows cold air and after 20 miles or so it will start getting warm. It then starts blowing cold again. It goes back and forth like this while running.

by in Pelham, GA on March 17, 2011
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1 answer
ANSWER by , March 18, 2011
Sounds like a classic thermostat issue. However, if the engine is hot enough, it could be a temperature blend issue inside the dash.