Heater Performance

HEATER PERFORMANCE

Before performing the following tests, see 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 A/C System Performance Test A/C Performance.

HEATER PERFORMANCE TEST

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 HVAC housing floor outlets. Compare the test thermometer reading to the Heater Temperature Reference chart.

HEATER TEMPERATURE REFERENCE






See Cooling system 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 causes of insufficient engine coolant flow are as follows:

- Improper heater hose routing.
- Low engine coolant.
- Pinched, kinked or plugged heater hoses.
- Plugged heater core.
- Plugged heater hose supply and return ports at the engine.

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 causes of insufficient heat:

- Inoperative A/C heater control or module (depending on ATC or MTC application).
- Inoperative blower motor system.
- Inoperative engine coolant thermostat.
- Inoperative, obstructed or improperly installed blend-air door(s).
- Inoperative or improperly installed blend door actuator or temperature control cable (depending on ATC or MTC application).
- Low engine coolant.
- Obstructed cowl air intake.
- Obstructed heater system outlets.

TEMPERATURE CONTROL

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

- A/C heater control (ATC system only).
- Blend-air door(s).
- Blend door actuator or temperature control cable, depending on system application.