have 2003S10 with 4.4 v6. hve no heat blowing,Thermostat?
First you need to determine if the engine is getting to operating temperature or not, the temperature gauge would be a good indication, if not then replace the thermostat, check that the heater hoses are getting hot, could be a air pocket or plugged heater core, and also make sure the climate control blend door actuators are working properly.
You might also check your heater core
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