This is the reason that it takes a while for heaters to start blowing warm air.
Until the engine warms up, there’s no heat for the heater core to extract.
Stuck Thermostats
Thermostats are valves that open and close depending on the temperature of the coolant.
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If the heater is blowing lukewarm instead of cold air, a stuck open thermostat could be the cause.
Air in the Cooling System
Another common problem triggers when air gets into the cooling system.
If that’s the case, the air bubbles must be flushed out to fix the problem.
Plugged Heater Core
Plugged heater cores can also cause a car’s heater to blow cold.
The best way to check for this is with a non-contact thermometer.
You use it to check whether coolant is flowing through the heater core.
If it isn’t, flushing the heater core often fixes the problem.
If that valve is stuck closed, that’s another reason a car heater will blow cold.
The fix for this is to open or remove the heater box and clean the fins.
Still, you’ve got the option to also have a mechanical, electrical, or vacuum problem.
When a blend door is stuck, it doesn’t matter if the heater core is working perfectly.
