Heater Performance Test

TEST
Pre-diagnostic Preparations

WARNING: REFER TO THE APPLICABLE WARNINGS AND CAUTIONS FOR THIS SYSTEM BEFORE PERFORMING THE FOLLOWING OPERATION.

Check the coolant level, drive belt tension, radiator air flow, and cooling fan operation. Start the engine and allow it to warm up to normal temperature.

Temperature Reference Table:

Maximum Heater Output: Test And Action
Engine coolant is provided to the heater system by two 16 mm (5/8 inch inside diameter) heater hoses. With the engine idling at normal running temperature, set the heater-A/C controls as follows. Temperature control to full Heat, Mode control to Floor, Blower control to the highest speed setting. Using a test thermometer, check the air temperature coming from the center floor outlets and compare this reading to the Temperature Reference table.

If the floor outlet air temperature is insufficient, check that the cooling system is operating to specifications. Both 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 heater system.

Possible Locations Or Cause Of Obstructed Coolant Flow
- Pinched or kinked heater hoses.
- Improper heater hose routing.
- Plugged heater hoses or supply and return ports at cooling system connections.
- Plugged heater core.
- Air locked heater core.
- Restrictor in backwards.

If coolant flow is verified and the heater floor outlet temperature is insufficient, a mechanical problem may exist.

Possible Location Or Cause Of Insufficient Heat
- Obstructed cowl air intake.
- Obstructed heater system outlets.
- Blend-air door not functioning properly.

Temperature Control
If heater floor outlet temperature cannot be adjusted with the heater-A/C control temperature control lever, one of the following could require service:
- Blend-air door binding.
- Faulty blend-air door motor.
- Improper engine coolant temperature.
- Faulty heater-A/C control.