Truck: 2000 sonoma
the heater in my truck starts of slightly warm but then start blowing cold air. how can i fix this?

As a test: Try asking for the warmest heat and shut the fan off or to lowest setting. Turn back on in a minute and see if it will blow heat for a short while. If so I'd bet the heater core isn't letting enough coolant thru it. If that works at all check the heater control valve in inlet heater hose and a flush of the whole cooling system would probably get this back in order,

T
Tom Greenleaf - MetroWest Boston - USA
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http://www.autoacsystems.com/tomgreenleaf/