Heater-a/c control. Heater performance

Heater-a/c control

Satisfactory heater and air conditioner performance depends upon proper operation and adjustment of all operating controls and refrigeration system components. For circuit descriptions and diagrams, refer to 8W-42 - Air Conditioning/Heater in Group 8W - Wiring Diagrams. These inspections, tests, and adjustments should be used to locate the cause of a malfunction.

Operation must be tested as described in the following sequence: (1) Move the temperature control knob quickly to the full hot and the full cold positions. There should be a distinct sound of the blend-air door hitting its stops within the heater-A/C housing at the end of  knob travel in each direction, with no spring-back of the knob. If not OK, inspect the condition, routing, installation and adjustment of the temperature control cable. See Temperature Control Cable in the Removal and Installation section and in the Adjustments section of this group for more information.

(2) Inspect and adjust the serpentine drive belt.

Refer to Group 7 - Cooling System for the procedures.

(3) Start the engine and hold the idle speed at 1,300 rpm.

(4) On vehicles with air conditioning, turn the temperature control knob to the extreme counterclockwise (Cool) position, and set the mode control switch knob in the Bi-Level (A/C) position. The outside (recirculation) air door should be open to outside air. If not OK, see Vacuum System in the Diagnosis and Testing section of this group.

(5) Open the vehicle windows. Test the blower motor operation in all speeds. If not OK, see Blower Motor in the Diagnosis and Testing section of this group. Leave the blower motor switch knob in the highest speed position.

(6) On vehicles with air conditioning, the compressor should be running and the air conditioning system in operation unless the ambient air temperature is below about -1 C (30 F). If not OK, see A/C Performance in the Diagnosis and Testing section of this group.

(7) Check the mode control switch operation. The heater and air conditioner systems should respond as described in the owner's manual in the vehicle glove box to each mode selected. Reduce the engine speed to normal idle. The vacuum will be high at low idle and the vacuum actuators should respond quickly. If not OK, see Vacuum System in the Diagnosis and Testing section of this group.

(8) If the vacuum tests, and the electrical component and circuit tests reveal no problems, disassemble the heater-A/C housing to inspect for mechanical misalignment or binding of the mode doors.

Heater performance

Before performing the following tests, refer to Group 7 - 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. Also be certain that the accessory vacuum supply line is connected at the engine vacuum source.

MAXIMUM HEATER OUTPUT

Engine coolant is delivered to the heater core through two heater hoses. With the engine idling at normal operating temperature, set the temperature control knob in the full hot position, the mode control switch knob in the floor position, and the blower motor switch knob in the highest speed position.

Using a test thermometer, check the temperature of the air being discharged at the heater-A/C housing floor outlets. Compare the test thermometer reading to the Temperature Reference chart.

If the floor outlet air temperature is too low, refer to Group 7 - Cooling System to check the engine coolant temperature specifications. 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 Group 7 - Cooling System for the procedures.

An alternate method of checking heater performance is to use a DRB scan tool to monitor the engine coolant temperature. The floor outlet air temperature reading should be no more than 4.5 C (40 F) lower than the engine coolant temperature reading.

OBSTRUCTED COOLANT FLOW

• Faulty water pump.
• Faulty 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:

• An obstructed cowl air intake
• Obstructed heater system outlets.
• A faulty, obstructed or improperly installed blend-air door.
• The temperature control cable is not connected, or is not routed or adjusted properly.
• A faulty blower system.
• A faulty heater-A/C control.

TEMPERATURE CONTROL

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

• A faulty heater-A/C control.
• The temperature control cable is not connected, or is not routed or adjusted properly.
• A faulty, obstructed or improperly installed blend-air door.
• An obstructed cowl air intake.
• The engine cooling system.