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Why does my car heater work but only blow cold air and how can I fix it?
Wiki User
∙ 13y ago
Actually, the heater is not working . . . only the fan. When heater controls are working, lack of heat output is due to lack of hot coolant running through the heater coil circuit which transfers heat from the engine to the cabin. This can arise when coolant is not reaching that circuit or when coolant flow is impeded or blocked in that circuit. Proceed through the following list of tests until correcting a problem restores heat output:
- Check the radiator fluid level. If coolant level is low, then less or no coolant is entering the heating coil supply circuit at the water pump. Next, or after topping off the radiator . . .
- Check for high engine temperature reading on instrument panel gauge; if reading is well above normal, turn off engine, let it cool to point were radiator hoses can be squeezed, and then . . .
- If coolant level rises (as if to overflow the filler tube) but does not circulate, immediately switch off engine and then replace thermostat.
- If coolant circulates, turn off engine, replace radiator cap and go to next step.
- Remove radiator cap, check/replenish coolant level, start engine, and watch for coolant to start flowing (not rising) in radiator.
- Check for high engine temperature reading on instrument panel gauge; if reading is well above normal, turn off engine, let it cool to point were radiator hoses can be squeezed, and then . . .
- Check for water circulation through the radiator . . .
- If one hose is hot (and hard) and the other is not, then a blockage (or rupture) has occurred in the heater coil, which will need to be replaced.
- If both hoses are warm to hot and misting of interior windshield is occurring (especially with defroster on), then the heater coil is leaking (coolant vapors into the fan driven air stream), and will need to be replaced.
- With the engine at normal operating temperature, feel the hoses leading from the water pump at engine "front" (where belts are situated):
- If all tests above pass, then there is an electrical or mechanical defect in the warm-cold air mixing and channelling subsystems. . . . typically requiring resort to qualified service personnel.
Wiki User
∙ 13y ago
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