2001 Dodge Intrepid Blow cold air, then warm, then cold aga

You would never have heat if the heater core was plugged.

First check the coolant level. Low coolant will cause intermittent flow through the heater core. If it's full, have your mechanic perform a "sniff" test at the overflow reservoir. This is where he draws AIR from the cooling system through a tube with a dark blue liquid. If the liquid turn bright yellow, combustion gases are getting into the cooling system from a leaking head gasket. The air bubbles will disrupt coolant flow. If it's really bad, you will see air bubbles in the reservoir while the engine is running.

If it continues to blow cold for more than a few minutes, that will give you time to run under the hood and feel the two heater hoses. If they are hot, suspect a problem with the computer controller that runs the air and temperature doors. Older cars used levers and cables and never had these problems, but engineers today can't make anything simple and reliable. They need computer controls to really screw things up. These controllers can develop intermittent connections on the connector pins. Soldering them may solve the problem.

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