Why my heat blowing cold air

If you engine temperature gauge is reading too low this could indicate the thermostat is sticking open and not allowing the engine to reach operating temperature. You could also be having an issue with a blend door actuator or door.These are located behind the dash and control air flow. Sometimes they can make a clicking noise when there is an issue. Alex

Start by checking your coolant level with the engine off and cold. If its low this will cause a lack of heat as well.

Thermostat failures are very common - check engine light normally turns on.