Heater Performance Test

HEATER PERFORMANCE

Before performing the following tests, check the engine coolant level and flow, engine coolant reserve/recovery system operation, accessory drive belt condition and tension, radiator air flow and both radiator and condenser fan operation. Perform the A/C System Performance Test, which is found within the HVAC System Test. If any diagnostic trouble codes (DTCs) are found in the A/C-heater control or the powertrain control module (PCM) or engine control module (ECM) (depending on engine application), repair as necessary.

MAXIMUM HEATER OUTPUT: TEST AND ACTION

Engine coolant is delivered to 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 HVAC housing 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 (refer to Cooling System for more information).

If the heater outlet air temperature degrades significantly at an idle, check for proper operation of the auxiliary electric coolant pump Operation.

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
- A plugged heater core

If proper coolant flow through the cooling system is verified, and heater outlet air temperature is still 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 or actuator not functioning properly
- Inoperative auxiliary electric coolant pump
- Inoperative 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 (ATC)
- Inoperative blend door cable (MTC)
- Inoperative, obstructed or improperly installed blend-air door
- Inoperative related wiring harness or connectors
- Improper engine coolant temperature