heaters on most cars at simply a small heat exchanger (LIKE A MINI RADIATOR) WITH HOT COOLANT FLOWING THRU THEM, YOUR UNDER DASH FAN PUMPS AIR THRU THAT MINI RADIATOR TO HEAT THE CABIN AREA
Ok obviously theres two seperate areas of concern or factors, ones ,air flow and the others hot coolant,flow, if the fan blows air thru the heat exchanger and its not blowing hot air its usually a coolant flow restriction, if theres no air flow its usually a ducting or fan issue,youll first need to isolate the problem.
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theres switches that control the under dash duct passages and baffle doors,that route air flow, that are sometimes vacuum operated and sometimes electric,if electic, a solinoid could be faulty or a blown fuse or bad connector could be the cause, if its vaccuum obviously a hose could be leaking or disconnected,potentially causing the ducting not to work correctly. youll need to find out first if your getting hot coolant thru the heat exchanger, (disconnect the heater hoses and force coolant or a garden hose water flow thru to verify that its not blocked) if your not getting coolant flow, youll need to correct the restriction, if your getting hot coolant flow, its duct work or the fan and youll need to verify and correct the restriction to air flow.
a partly defective water pump, or coolant fitting could also be a problem
YES READING THE LINKS IS WORTH THE TIME
http://wiki.answers.com/Q/Why_would_a_truck_heater_only_blow_cold_air
http://wiki.answers.com/Q/Why_would_the_car_heater_not_blow_any_air
http://auto.howstuffworks.com/cooling-system10.htm
http://www.familycar.com/Classroom/CoolingSystem.htm
http://www.2carpros.com/first_things/heater_failure.htm
http://www.allpar.com/fix/heat.html
Ok obviously theres two seperate areas of concern or factors, ones ,air flow and the others hot coolant,flow, if the fan blows air thru the heat exchanger and its not blowing hot air its usually a coolant flow restriction, if theres no air flow its usually a ducting or fan issue,youll first need to isolate the problem.
.
theres switches that control the under dash duct passages and baffle doors,that route air flow, that are sometimes vacuum operated and sometimes electric,if electic, a solinoid could be faulty or a blown fuse or bad connector could be the cause, if its vaccuum obviously a hose could be leaking or disconnected,potentially causing the ducting not to work correctly. youll need to find out first if your getting hot coolant thru the heat exchanger, (disconnect the heater hoses and force coolant or a garden hose water flow thru to verify that its not blocked) if your not getting coolant flow, youll need to correct the restriction, if your getting hot coolant flow, its duct work or the fan and youll need to verify and correct the restriction to air flow.
a partly defective water pump, or coolant fitting could also be a problem
YES READING THE LINKS IS WORTH THE TIME
http://wiki.answers.com/Q/Why_would_a_truck_heater_only_blow_cold_air
http://wiki.answers.com/Q/Why_would_the_car_heater_not_blow_any_air
http://auto.howstuffworks.com/cooling-system10.htm
http://www.familycar.com/Classroom/CoolingSystem.htm
http://www.2carpros.com/first_things/heater_failure.htm
http://www.allpar.com/fix/heat.html