If the heater blows even when the controls are set to "Off", then your issue is with the control unit on the dash. You'll need to trace the wiring with a voltmeter for any shorts/breaks in the wire. Also, check the condition of the connectors and pins inside.
Keep in mind, sometimes the control unit fails and needs to be replaced.
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Tuesday, February 15th, 2011 AT 2:11 PM