Diagnostic Starting Point - Heating, Ventilation & Air Conditioning

The Heating, Ventilation and Air Conditioning (HVAC) system is divided into three separate sections. The first, Heating, Ventilation and Air Conditioning, has all procedures that pertain to a HVAC component or function that is not specifically associated with an automatic or manual control system. The second, HVAC Systems - Manual, has all procedures specific to the manual control system. The third, HVAC Systems - Automatic, has all procedures specific to the automatic control system.

Begin the system diagnosis with the:

• SYMPTOMS - HVAC SYSTEMS - MANUAL for a system without DTCs
• DIAGNOSTIC SYSTEM CHECK - HVAC SYSTEMS - AUTO for a system with DTCs

The Diagnostic System Check will provide the following information:

• The identification of the control module(s) which command the system.
• The ability of the control module(s) to communicate through the serial data circuit.

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Review the Description and Operation information to help you determine the correct symptom diagnostic procedure when a malfunction exists. Reviewing the Description and Operation will also help you determine if the condition described by the customer is normal operation.

The HVAC Description and Operation information is divided into:

• AIR DELIVERY DESCRIPTION & OPERATION in HVAC Systems - Manual
• AIR TEMPERATURE DESCRIPTION & OPERATION in HVAC Systems - Manual
• AIR DELIVERY DESCRIPTION & OPERATION in HVAC Systems - Automatic
• AIR TEMPERATURE DESCRIPTION & OPERATION in HVAC Systems - Automatic

The Air Delivery Description and Operation contains the following topics:

• Air Speed
• Air Distribution

The Air temperature Description and Operation contains the following topics:

• Heater Mode
• A/C Mode
• A/C Cycle