Heating System Diagnosis

Fig 7 Temperature Reference:

WARNING: Review the Service Precautions before performing the following procedures.

PREPARATIONS
Check the radiator coolant level, serpentine drive belt tension. and engine vacuum line connections. Also check the radiator air flow and the radiator fan operation. Start the engine and allow it to warm up to normal operating temperature.

WARNING: Do not remove the radiator pressure cap when the engine is at operating temperature, personal injury may result.

If the vehicle has been operated recently, wait fifteen minutes or longer before removing the radiator pressure cap. Place a rag over the cap and turn it to the first safety stop. Allow any pressure to escape through the overflow tube. When the system stabilizes, remove the cap completely.

MAXIMUM HEATER OUTPUT
Engine coolant is delivered to the heater core through two heater hoses. With the engine idling at normal operating temperature, set the temperature control knob in the full hot position, the mode control switch knob in the Floor position, and the blower motor switch knob in the highest speed position. Using a test thermometer, check the air temperature coming from the floor outlets, refer to the Temperature Reference chart.

If the floor outlet air temperature is low, refer to Cooling System for the coolant temperature specifications. Both of the heater hoses should be hot to the touch. The coolant return hose should be slightly cooler than the supply hose. If the coolant return hose is much cooler than the supply hose, locate and repair the engine coolant flow obstruction in the heater system.

OBSTRUCTED COOLANT FLOW
Possible locations or causes of obstructed coolant flow:
- Pinched or kinked heater hoses.
- Improper heater hose routing.
- Plugged heater hoses or supply and return ports at the cooling system connections (refer to Cooling System).
- A plugged heater core.

If proper coolant flow through the heater system is verified, and outlet air temperature is still low, a mechanical problem may exist.

MECHANICAL PROBLEMS
Possible locations or causes of insufficient heat:
- An obstructed cowl air intake.
- Obstructed heater system outlets.
- A blend-air door not functioning properly.

TEMPERATURE CONTROL
If the heater discharge air temperature cannot be adjusted with the temperature control knob on the heater-A/C control panel, the following could require service.
- The heater-A/C control.
- The temperature control cable.
- The blend-air door.
- Improper engine coolant temperature.