Two problems related to defogger have been reported for the 1998 Chevrolet S10. The most recently reported issues are listed below.
When heater control knob on dash is in blue or cold setting ,and contol if off,hot air of 110 degrees is noticed in foot air duct area. Also, when control is in passenger floor position and temp control in blue or cold air area, hot air still blows. Cannot get outside fresh air in interior without getting hot air. Only way to cool off cabin is to run air conditioning. Suspect that air blower duct relay,actuator, or vent door is not being regulated properly to channel the air in proper manner. Taken to dealer and they are checking.
Heating system continuously runs and cannot be manually turned off, cause unknown. Please give any further details.