no heat from your vents? where to look

cold air from the heater when the engine is up to temperature is one of those faults with several possible causes, most of them cheap and one of them not.

work through them in order of likelihood.

1. low coolant

the commonest cause by a distance. the heater core sits high in the system, so it is the first thing to be starved when the coolant level drops.

low coolant is not normal. it went somewhere, and finding out where matters more than topping it up.

2. a stuck thermostat

a thermostat stuck open means the engine never reaches proper temperature, so there is no hot coolant to give the heater. the temperature gauge sitting lower than usual, particularly on the highway, is the tell.

3. the blend door

modern cars mix hot and cold air with a flap, moved by a small actuator motor. when the actuator fails you get one temperature regardless of what you select, and often a clicking from behind the dashboard.

common, and typically the cause when one side of the car has heat and the other does not.

4. the coolant control valve

some vehicles use a valve, vacuum or electrically operated, to control coolant flow to the heater core. if it fails closed, no hot coolant reaches the core and the heater blows cold with everything else working perfectly.

on a vacuum-operated one, the failure is often a perished vacuum hose rather than the valve itself, which is a very cheap fix once it is found.

5. a blocked heater core

the expensive one. years of old coolant leave deposits, and the narrow passages in the core silt up. sometimes it can be flushed. sometimes it means replacing the core, which on many vehicles is behind the entire dashboard.

the one that is not about heat at all

if your windows fog and smell sweet and the carpet on the passenger side is damp, the heater core is leaking coolant into the cabin. do not ignore that one, and do not keep breathing it.

where to start

coolant level, then the temperature gauge on a drive. those two cost nothing and rule out the two commonest causes before anybody opens a dashboard.