Before performing the following tests, see COOLING for the procedures to check the engine coolant level and flow, engine coolant reserve/recovery system operation, accessory drive belt condition and tension, radiator air flow and the fan drive operation.

WARNING: Do not remove radiator cap when engine is hot. Failure to follow this instruction may result in serious injury.

If vehicle has been run recently, wait 15 minutes before removing the radiator cap. Place a rag over the cap and turn it to the first safety stop. Allow pressure to escape through the overflow tube. When the system pressure stabilizes, remove the cap completely.

MAXIMUM HEATER OUTPUT

Engine coolant is delivered to and from the heater core through two heater hoses. With the engine idling at normal operating temperature, set the temperature control to the full hot position, the mode control to the floor position, and the blower motor control to the highest speed position. Using a test thermometer, check the temperature of the air being discharged at the front floor outlets. Compare the test thermometer reading to the Heater Temperature Reference chart.

HEATER TEMPERATURE REFERENCE

See COOLING if the heater outlet air temperature is below the minimum specification. Both of the heater hoses should be hot to the touch. The coolant return heater hose should be slightly cooler than the coolant supply heater hose. If the return hose is much cooler than the supply hose, locate and repair the engine coolant flow obstruction in the cooling system.

OBSTRUCTED COOLANT FLOW

Possible locations or causes of obstructed coolant flow are as follows:

• Low coolant level
• Inoperative water pump
• Inoperative thermostat
• Pinched or kinked heater hoses
• Improper heater hose routing
• Plugged heater hoses or supply and return ports at the cooling system connections
• Plugged heater core

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

MECHANICAL PROBLEMS

Possible causes of insufficient heat due to mechanical problems are as follows:

• Obstructed cowl air intake
• Obstructed heater system outlets
• Inoperative engine thermostat
• Inoperative blower motor system
• Inoperative A/C-heater control
• Inoperative blend door actuator(s)
• Inoperative, obstructed or improperly installed blend-air door(s)

TEMPERATURE CONTROL

If the heater outlet air temperature cannot be adjusted with the temperature control on the A/C-heater control, the following could require service:

• Inoperative A/C-heater control
• Inoperative blend door actuator(s)
• Inoperative, obstructed or improperly installed blend-air door(s)
• Improper engine coolant temperature

SPECIFICATIONS

A/C SYSTEM

FASTENER TORQUE

SPECIAL TOOLS

Fig. 4: Trim Stick C-4755

Fig. 5: Back Probe Tool 6801

Fig. 6: Pliers, A/C Snap Ring 9764