The heater is blowing cold air

Drive in today

General guidance for this symptom. A warning light that is flashing or an overheating engine: stop driving and call.

Likely causes

• Low coolant

  The heater core usually sits high in the system, so it is the first place to run dry when the level drops. Air in the system after a top-off can do the same thing. Low coolant also means less protection against overheating.

  Coolant flush and cooling system service
• A thermostat stuck open

  If the thermostat never closes, the engine runs cool, the temperature gauge sits lower than usual and the heater only gets lukewarm. A repair shop replaces thermostats.

  Multi-point maintenance check
• A clogged heater core

  Old coolant breaks down and leaves scale. The narrow heater core passages are often where it collects first, and flow drops off over time.

  Coolant flush and cooling system service
• A blend door or control fault

  If the engine is warm, the coolant is full and both heater hoses are hot, the problem is inside the dash: a door actuator or control that will not move to the heat side. That is repair shop work.

  Multi-point maintenance check

Your heater is a small radiator behind the dash that borrows heat from engine coolant. If the coolant is low, never gets hot, or cannot flow through that small radiator, the fan blows outside-temperature air. On a Gardnerville morning in January that is miserable, and it also clears the windshield poorly, which makes it a safety issue on US-395 before sunrise.

Three things to notice before you come in

• Where the temperature gauge sits once warmed up, compared with what you are used to
• Whether the air gets warm at highway speed but cold at idle (often low coolant or air in the system)
• Whether the fan blows hard or barely moves air (weak airflow points to the blower or a clogged cabin filter)

A weak fan is a different problem from cold air. A cabin air filter that is packed with dust and smoke residue can choke airflow, and that one we replace in the bay.

What we check and what we hand off

We check the coolant level and strength, look for leaks at hoses and the radiator, and check the cabin filter. If the coolant is low or worn out, a coolant flush replaces it with the type your manual lists and purges air from the system. A flush can sometimes restore flow through a partly scaled heater core, though it cannot clear a fully blocked one.

Thermostats, heater core replacement and dash controls are repairs we do not perform. We tell you what we found and point you to a repair shop. You decide.

Why it shows up in the first cold week

Reno averages about 122 nights a year at or below freezing, Carson City about 146 and Minden about 188 (NOAA 1991-2020 normals). A heater that was only a little weak in October becomes obvious in November. The Car Care Council suggests checking the cooling system before winter for this reason, and our before-winter checklist includes it.