Diagnostic System Check - HVAC System - Automatic

A Diagnostic System Check:

Process Description
The heater-A/C control diagnostic system check is an organized approach to identify problems associated with the heater-A/C control. This check must be the starting point for any heater-A/C control complaint, and it will direct you to the next logical step in diagnosing the trouble condition. The heater-A/C control is a very reliable component and is not likely the cause the malfunction. Most system complaints are linked to faulty wiring and connectors, and occasionally to components. Understanding the heater A/C-control and using the diagnostic tables correctly will reduce diagnostic time and prevent unnecessary parts replacement.

Diagnostic Aids
The diagnostic aids include the history and current trouble codes and the related diagnostic tables.
^ The following conditions may result in an intermittent operation of the heater-A/C control with no Diagnostic Trouble Codes (DTCs) stored:
- Any condition which results in the interruption of power to the heater-A/C control.
- Out of range battery or ignition voltage specification. Normal battery or ignition voltage: 9V-1 6V.
- A loose or damaged ground(s).
- An open or short in the Class 2 serial data link.
^ An intermittent failure in the electronic system may be very difficult to detect and accurately diagnose. The heater-A/C control tests for different malfunctions under different vehicle conditions. For this reason, a thorough test drive is often needed in order to repeat a fault condition. If the system malfunction is not repeated during the test drive, a good description of the complaint may be very useful in locating an intermittent fault condition. Faulty electrical connections or wiring cause most intermittent problems. When an intermittent 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 wire-to-terminal connections.
- Dirty or corroded terminals.
- Damage to connector bodies.
^ Use J 35616-A whenever a diagnostic procedure requests probing or checking a terminal. Use this adapter in order to ensure that no damage to
^ Use Scan Tool in order to read the DTCs set by the system. If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving the 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. Refer to Intermittents and Poor Connections for more information. Intermittents and Poor Connections
^ Exit all the scan tool tests before cycling the ignition switch from the off to the on position unless you are directed otherwise. Follow the operating instructions in the scan tool user manual. Failure to follow these instructions may set DTCs, cause vehicle system malfunctions, set false DTCs, or cause scan tool malfunctions.
^ Check all relative fuses (see schematic) for the heater-A/C control. If open, check the circuits which are fed power by these fuses for a short to ground.
^ Make sure all relative grounds are clean and tight.
^ For heater-A/C control service procedures, refer to Control Assembly Replacement
^ Check for a broken (or partially broken) wire inside of the insulation which could cause system malfunction but prove good in a continuity/voltage check with a system disconnected. These circuits may be intermittent or resistive when loaded, and if possible, should be checked by monitoring for a voltage drop with the system operational (under load).
^ Check for proper installation of the aftermarket electronic equipment which may affect the integrity of other systems.

Tools Required
Use the following special tools in order to complete the diagnostics:
^ J 34142-B Unpowered Test Light
^ J 35616-A Connector Test Adapter kit
^ J 39200 Digital Multimeter
^ Diagnostic Scan Tool

Function Check
1. The following conditions indicate that the electrical circuits are functioning correctly:
^ The air conditioning blower motor operates at the appropriate speed with the control (mode) in any position except OFF. Verify that the compressor clutch also engages.
^ The blower motor will not operate in any speed with the control in the OFF position.
2. The heater A/C control assembly (mode selector) is operating correctly when the designated outlets distribute air.

Perform the following A/C Function Tests.

Preliminary Checks:
^ Inspect for temperature change when the temperature knob position is changed. On dual control systems Inspect the left side and right side outlets when the temperature control position is changed.
^ Listen for a decrease in air noise, due to the closing of the recirculation valve, when going from MAX mode to A/C mode.
^ Inspect all of the I/P outlets. Verify that the following conditions exist:
- The barrel rotates
- The vane operates
- The barrel and vanes hold the present position in HI blower operation.