For 1990-2009 cars

Important: Review the system operation in order to learn the system functions. Refer to the following procedures:

• | Air Delivery Description and Operation

• | Air Temperature Description and Operation

### Visual/Physical Inspection

• | Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to Checking Aftermarket Accessories in Wiring Systems.

• | Inspect the system components which are easily accessible or visible for obvious damage or for conditions which could cause the symptom.

• | Verify the A/C compressor clutch turns freely and is not seized.

• | The A/C compressor will not operate in cold, outside air temperatures. Refer to Air Temperature Description and Operation .

• | The following conditions may cause window fogging:

- | A wet carpet

- | High humidity

- | An interior water leak

- | A blocked drain tube to the A/C evaporator

- | Maximum passenger capacity

- | Blocked body pressure relief valves

• | Inspect the air distribution system for causes of reduced airflow:

- | An obstructed or dirty passenger compartment air filter

- | Blocked or damaged air vents

### Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

### Symptom List

Refer to one of the following symptom diagnostic procedures:

• | HVAC Compressor Clutch Does Not Engage

• | HVAC Compressor Clutch Does Not Disengage

• | Blower Motor Always On

• | Blower Motor Inoperative

• | Blower Motor Malfunction

• | Too Hot in Vehicle

• | Too Cold in Vehicle

• | Air Delivery Improper

• | Air Recirculation Malfunction

• | Leak Testing in Heating, Ventilation and Air Conditioning

• | Defrosting Insufficient in Heating, Ventilation and Air Conditioning

• | Noise Diagnosis - Blower Motor in Heating, Ventilation and Air Conditioning

• | Noise Diagnosis - Air Conditioning (A/C) System in Heating, Ventilation and Air Conditioning

• | Noise Diagnosis - HVAC Module in Heating, Ventilation and Air Conditioning

• | Odor Diagnosis in Heating, Ventilation and Air Conditioning