Heater Performance Test

PRE-DIAGN0STIC PREPARATIONS
Review Safety Precautions and Warnings before performing the following procedures.

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

WARNING: DO NOT REMOVE RADIATOR CAP WHEN ENGINE IS HOT, PERSONAL INJURY CAN RESULT.

If vehicle has been run recently wait 15 minutes before removing 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 stabilizes, remove the cap completely.

Temperature Reference Chart:

MAXIMUM HEATER OUTPUT
Engine coolant is provided to the heater system by two 16 mm (5/8 in.) inside diameter heater hoses. With engine idling at normal running temperature, set the control to maximum heat, floor, and high blower setting. Using a test thermometer, check the air temperature coming from the floor outlets, refer to Temperature Reference chart.

If the floor outlet air temperature is insufficient, refer to Cooling Systems for specifications. Both heater hoses should be HOT to the touch (coolant return hose should be slightly cooler than the supply hose). If coolant return hose is much cooler than the supply hose, locate and repair engine coolant flow obstruction in heater system.

POSSIBLE CAUSE OF LOW OR OBSTRUCTED COOLANT FLOW
1. Pinched or kinked heater hoses.
2. Improper heater hose routing.
3. Plugged heater hoses or supply and return ports at cooling system connections.
4. Plugged heater core.
5. Air locked heater core or air in cooling system.
6. If coolant flow is verified and outlet temperature is insufficient, a mechanical problem may exist.
7. Low coolant level.
8. Low water pump flow.

POSSIBLE CAUSE OF INSUFFICIENT HEAT
1. Obstructed cowl air intake.
2. Obstructed heater system outlets.
3. Blend-air door not functioning properly.
4. Evaporator freeze up.

TEMPERATURE CONTROL
If temperature cannot be adjusted with the TEMP knob on the control panel, the following could require service:
1. Blend-air door binding.
2. Improper engine coolant temperature.
3. Faulty Instrument Panel Control.
4. Wiring or a fuse problem.