Maximum Heater Output

Heater System Diagnosis:

Possible causes of insufficient heater output, or a lack of temperature control, include:
- Obstructed heater outlets
- Insufficient vacuum supply to the water valve, or a faulty water valve
- Insufficient engine coolant level
- Faulty thermostat
- Blend-air (temperature control) door misdirected, or binding
- Blend-air (temperature control) door control cable out of adjustment
- Plugged or obstructed heater hose, or heater core.