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Makes 🢒 Buick 🢒 1999 🢒 Century (China) (CNG) 🢒 General Information 🢒 General Information 🢒 Functional Check

Functional Check CJ4

The HVAC control assembly uses information from other systems in order to deliver information to the driver. Therefore, before further diagnosis, review the general information on how the HVAC system operates and how each system interacts with the HVAC control assembly. This will save diagnostic time, future misdiagnosis, and unnecessary parts replacement.

Use a scan tool to diagnose the HVAC control assembly when referred to in diagnostic procedures. In addition to displaying Diagnostic Trouble Codes (DTCs), the scan tool will display the input status and the data values used. The scan tool can also cycle many of the heater-A/C control outputs and indicators both on and off. Any of these features can be selected using the scan tool.

Become very familiar with the HVAC control assembly capabilities and diagnostic features. These self-diagnostic features are referenced in the DTC table and are very useful in diagnosing non-DTC setting malfunctions as well. Notice that not all circuits feeding information to the HVAC control assembly will set a DTC if a fault exists within that circuit. Some of these circuits such as the heater solenoid coil output, the heater/defrost solenoid coil output and the recirc solenoid coil output will not set a DTC. Diagnostic tables concerning these circuits are still included to help locate concerns.

Replace the HVAC control assembly only if the diagnostic procedures specifically direct you to do so. The HVAC control assembly does not automatically need to be replaced when a short is found in the wiring. Repair the wiring first, then check the heater-A/C control for further concerns. Most system malfunctions are traceable to faulty wiring and connectors, and occasionally components. The HVAC control assembly is very reliable and usually is not the cause of the malfunction.

  1. The following conditions indicate that the electrical circuits are functioning correctly:
    2. • 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 HVAC 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 front and rear 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 RECIRC mode to OUTSIDE AIR 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 HIGH blower operation.

HVAC System Check -- CJ4

Step

Action

Value(s)

Yes

No

1
  1. Turn the ignition switch to the ON position.
  2. Observe the HVAC control assembly display.

Is the HVAC control assembly display on?

--

Go to Step 2

Go to Interior Lights Dimming System Check

2
  1. Place the front HVAC control assembly in the FRONT DEFROST mode.
  2. While listening to the blower motor, change the blower speed using the fan speed control from LOW to HIGH on the HVAC control assembly.

Does the blower motor turn on and change speed?

--

Go to Step 3

Go to HVAC Blower Controls System Check

3

Test each of the air flow modes by selecting the individual modes with the MODE control on the HVAC control assembly.

Does the air flow move through the proper vents for each mode?

--

Go to Step 4

Go to HVAC Air Delivery System Check

4

Slide the front HVAC control assembly from full cold (blue) to full hot (red).

Does the front air temperature control operate properly?

Go to Step 5

Go to Driver Temperature Control Inoperative

5

Slide the rear HVAC control assembly temperature control from full cold to full hot.

Does the rear air temperature control operate properly?

--

Go to Step 6

Go to Passenger Temperature Control Inoperative

6
  1. Press the front HVAC control assembly A/C button ON.
  2. Place the temperature control to the LOW setting.

Does the A/C compressor turn on and off properly when using the A/C system?

--

Go to Step 7

Go to Powertrain On Board Diagnostic (OBD) System Check

7
  1. Press the front HVAC control assembly A/C button OFF.
  2. Press the rear HVAC control assembly A/C button ON.
  3. Place the temperature control to the LOW setting.

Does the A/C compressor turn on and off properly when using the A/C system?

--

Go to Step 8

Go to Powertrain On Board Diagnostic (OBD) System Check

8
  1. Turn the ignition switch to the OFF position
  2. Install a scan tool to the Data Link Connector (DLC).
  3. Attempt to establish communication with the HVAC control assembly.

Has communications been established

--

Go to Step 9

Go to DTC U1255 Serial Data Line Malfunction

9

Check for HVAC trouble codes.

Are there any HVAC current or history trouble codes stored?

--

Go to Diagnostic Trouble Code (DTC) List

System OK

Functional Check C60

The HVAC control assembly uses information from other systems in order to deliver information to the driver. Therefore, before further diagnosis, review the general information on how the HVAC system operates and how each system interacts with the HVAC control assembly. This will save diagnostic time, future misdiagnosis, and unnecessary parts replacement.

Use a scan tool to diagnose the HVAC control assembly when referred to in diagnostic procedures. In addition to displaying Diagnostic Trouble Codes (DTCs), the scan tool will display the input status and the data values used. The scan tool can also cycle many of the heater-A/C control outputs and indicators both on and off. Any of these features can be selected using the scan tool.

Become very familiar with the HVAC control assembly capabilities and diagnostic features. These self-diagnostic features are referenced in the DTC table and are very useful in diagnosing non-DTC setting malfunctions as well. Notice that not all circuits feeding information to the HVAC control assembly will set a DTC if a fault exists within that circuit. Some of these circuits such as the heater solenoid coil output, the heater/defrost solenoid coil output and the recirc solenoid coil output will not set a DTC. Diagnostic tables concerning these circuits are still included to help locate concerns.

Replace the HVAC control assembly only if the diagnostic procedures specifically direct you to do so. The HVAC control assembly does not automatically need to be replaced when a short is found in the wiring. Repair the wiring first, then check the heater-A/C control for further concerns. Most system malfunctions are traceable to faulty wiring and connectors, and occasionally components. The HVAC control assembly is very reliable and usually is not the cause of the malfunction.

  1. The following conditions indicate that the electrical circuits are functioning correctly:
    2. • 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 HVAC 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.
    • Listen for a decrease in air noise, due to the closing of the recirculation valve, when going from REVIRC mode to OUTSIDE AIR 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 HIGH blower operation.

Step

Action

Value(s)

Yes

No

1
  1. Turn the ignition switch to the ON position.
  2. Observe the HVAC control assembly display.

Is the HVAC control assembly display on?

--

Go to Step 2

Go to Interior Lights Dimming System Check

2
  1. Place the HVAC control assembly in the DEFROST mode .
  2. While listening to the blower motor, change the blower speed using the fan speed control from LOW to HIGH on the HVAC control assembly.

Does the blower motor turn on and change speed?

--

Go to Step 3

Go to HVAC Blower Controls System Check

3
  1. Press the A/C button on the HVAC control assembly.
  2. Place the temperature control to the cold (blue) setting.

Does the A/C compressor turn on and off properly when using the A/C system?

--

Go to Step 4

Go to HVAC Compressor Controls System Check

4

Test each of the air flow modes by selecting the individual modes with the MODE control on the HVAC control assembly.

Does the air flow move through the proper vents for each mode?

--

Go to Step 5

Go to HVAC Air Delivery System Check

5

Turn the temperature control from full cold (blue) to full hot (red).

Does the air temperature control operate properly?

System OK

Go to Temperature Control Inoperative