System Check - Air Delivery - HVAC System - Automatic

Air Delivery System Check:

HVAC Air Delivery System Check

CIRCUIT DESCRIPTION
The Air Delivery System Check is an organized approach to identify problems associated with the heater & A/C control ability to control air delivery. This check must be the starting point for any air delivery complaint, and will direct you to the next logical step in diagnosing the complaint. The heater and A/C control is a very reliable component and is not likely the cause of the malfunction. Most system complaints are linked to faulty wiring and connectors, and occasionally to components. Understanding the computer system and using the tables correctly will reduce diagnostic time and prevent unnecessary pans replacement.

DIAGNOSTIC AIDS
^ The following conditions may result in an intermittent operation of the heater and A/C control with no DTC stored:
- Any condition which results in the interruption of power to the heater and A/C control.
- Out of range battery or ignition voltage.
- A loose or damaged ground(s).
^ An intermittent failure in the electronic system may be very difficult to detect and to accurately diagnose. A good description of the complaint may be very useful in locating an intermittent malfunction. Faulty electrical connections or wiring causes most intermitting problems. When an intermitting condition is suspected, check the suspected circuits for the following conditions:
- Poor mating of connector halves or backed out terminals
- Improperly formed or damaged terminals
- Wire chafing
- Poor wire to terminal connections
- Dirty or corroded terminals
- Damage to connector bodies
^ If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving related wiring and connectors. This can often cause the malfunction to occur. Perform a thorough inspection of all related wiring and connectors pertaining to the history DTC stored.

TEST DESCRIPTION
The number(s) below refer to the step number(s) on the diagnostic table.
1. This test determines if communications can be established with the heater and A/C control.
2. This step checks for stored current heater and A/C control DTCs.
3. This step checks for stored history or current intermittent DTCs.
6. This step checks the overall function of the heater and A/C control system. A good base can be established by allowing the engine to reach operating temperature, selecting maximum blower speed and the coldest temperature setting. From this base all facets of the system can be checked (heating, cooling and air delivery.)
12. This step checks the available refrigerant charge in the system. A reading of 55 psi and above usually indicates there is enough refrigerant in the system. The contacts in the A/C compressor refrigerant pressure switch remain closed thus allowing the compressor to operate.
13. If the pressure readings were lower than 55 psi in the previous step, the refrigerant charge is low. A leak check on the system needs to be performed.