Heater Performance

HEATER PERFORMANCE

Before performing the following tests, refer to Cooling System 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. Perform the HVAC System Test. If any diagnostic trouble codes (DTCs) are found in the A/C-heater control, powertrain control module (PCM) or engine control module (ECM) (depending on engine application), gateway module or totally integrated power module (TIPM), repair as necessary.

MAXIMUM HEATER OUTPUT: TEST AND ACTION

Engine coolant is provided to the heater system through two heater hoses. With the engine idling at normal operating temperature, set the temperature control to maximum heat 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 from the floor outlets. Compare the test thermometer reading to the Heater Temperature Reference chart.







If the heater outlet air temperature is below the minimum specification, refer to Cooling System. 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:

- 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 locations or causes of insufficient heat due to mechanical problems are as follows:

- Obstructed cowl air intake.
- Obstructed heater system outlets.
- Blend-air door(s) or actuator(s) not functioning properly.
- Faulty blower motor system
- Inoperative A/C-heater control

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.
- Inoperative related wiring harness or connectors.
- Improper engine coolant temperature.