Output Temperature Check (Heater)

The most likely causes of insufficient heating outside the heater system include the following conditions:
- A low coolant level
- A faulty thermostat
- A partially or fully clogged heater core or hose
- An obstruction of air circulation
- An air leak past a faulty seal into the passenger compartment

Heat Excessive
The most likely cause of excessive heat from the heater system is a bad temperature actuator. Other related causes of excessive heat include a faulty mode selector (control assembly), or an open or shorted electrical harness.

Heater Output Temperature Check
Inspect the heat output of the heater system with the following procedure:

Preparation
With the engine sufficiently cool, remove the radiator cap, start the engine, and allow the engine to idle. Set the heater controls to HTR mode, full Red (Hot) temperature, and HI blower speed. When coolant flow in the radiator is visible through the filler neck, install the radiator cap.

Temperature Check
When the engine is warmed up (after approximately 20 minutes of operation), drive the vehicle. Use an accurate thermometer in order to determine the outside air temperature and the temperature of the air discharged at the floor outlets with the vehicle being driven at 48 km/h (30 mph). Minimum acceptable heater output temperatures at four different outside air temperatures are shown in the table.

Steps 1 - 5:

Minimum acceptable heater output temperatures for outside air temperatures other than those shown can be approximated by using the Fahrenheit scale and rounding off the outside air temperature to the nearest 5° For every additional 5° of outside temperature, an additional 1.8° of heater output temperature should be allowed when the outside temperature is below 50°. An additional 1.6° of heater output temperature should be allowed for every 5° of outside temperature when the outside temperature is above 50°.