HVAC System Test (MTC)

HVAC SYSTEM TEST (MTC)

Theory of Operation
The HVAC System Test consists of three tests. Test 2 tests A/C system performance, Test 3 tests for mode switch, mode and temp pot, and door actuator circuit faults, Test 4 tests for door actuator calibration faults. Either perform all three tests for a complete system test or perform an individual test if diagnosing a specific symptom.

DIAGNOSTIC TEST

1. HVAC SYSTEM TEST

NOTE:
- An active DTC 33 will prevent the control from entering diagnostic mode and performing certain diagnostic functions, it will also prevent proper A/C mode switch and status indicator function as evidenced by not being able to turn the A/C status indicator either on or off. If this occurs, refer to A/C HEATER CONTROL WILL NOT ENTER DIAGNOSTIC MODE (MTC) for the diagnostic test procedure.
- An active DTC 34 will prevent the control from performing certain diagnostic functions and it will prevent proper EBL mode switch and status indicator function as evidenced by not being able to turn the EBL status indicator either on or off. If occurs, diagnose and repair DTC 34 before proceeding.
- Active DTCs must be resolved before diagnosing stored DTCs.

Choose a diagnostic test to perform.

Complete HVAC System Test
Go To 2
A/C System Performance Test
Go To 2
Mode Switch, Mode & Temp Pot, & Door Actuator CKT Test
Go To 3
Actuator Calibration Test
Go To 4

2. A/C SYSTEM PERFORMANCE TEST

NOTE: The following are prerequisites of the Cooldown Test. Verify each of the following before running the test:
- The test will not start if DTC 31 or 32 is active. If active, diagnose and repair the DTCs before proceeding.
- Verify that the blower motor operates correctly in all speeds. Diagnose and repair all blower related faults before proceeding.
- Verify that the work area ambient temperature is above 16° C (60° F) before proceeding. Move the vehicle to a warmer work area if necessary.
- Verify that the evaporator temperature is above 18.3° C (65° F) before proceeding.
- Verify that the A/C compressor is not running. If the compressor is running, turn the A/C off and allow the evaporator to warm up before proceeding.

Once all of the prerequisites have been met, actuate the Cooldown Test by performing the following:
- Turn the ignition off.
- Turn the blower control to off.
- Start the engine.
- Press the A/C mode switch down, turn the blower control to high speed, wait 3 seconds and then release the A/C mode switch.

NOTE:
- The Cooldown Test can take up to two minutes to run. The test will stop running if either the ignition or the blower is turned off or if DTC 31 or 32 sets during the test.
- Running the test will cause the EBL status indicator to flash. If the test passes, the EBL status indicator will stop flashing. If the test fails, both the EBL and A/C status indicators will flash alternately.

- Allow the test to run to completion before proceeding.

Turn the ignition off, wait 10 seconds, and turn the ignition on.
Actuate the Display DTC function by performing the following:
- Turn the blower control on.
- Press the A/C mode switch down, turn the blower control to off, wait 3 seconds and then release the A/C mode switch.

NOTE: The A/C status indicator displays active DTCs when the EBL status indictor is not illuminated and stored DTCs when the EBL status indicator is illuminated.

Q: Is the A/C status indicator flashing DTCs?

YES: Diagnose and Repair the DTC(s). Refer to HVAC related symptoms. Rerun the Cooldown Test after the repair is complete.
NO: As necessary, either Go To 3 or 4, or Perform BODY VERIFICATION TEST - VER 1. Body Verification Test

3. MODE SWITCH, MODE & TEMP POT, & DOOR ACTUATOR CIRCUIT TEST
If not do so previously, start the engine.
Turn the blower control on.
Turn the Blend control to full cold.
Turn the Mode control to panel.
Press the A/C mode switch on, wait 30 seconds, press it off, and then proceed to the next step.
Press the Rear Defrost mode switch on, wait 30 seconds, press it off, and then proceed to the next step.
Turn the Blend control to full hot, wait 30 seconds, turn it to full cold, and then proceed to the next step.
Turn the Mode control to every door position. Leave it in each position for 30 seconds. When complete, proceed to the next step.
Turn the ignition off, wait 10 seconds, and turn the ignition on.
Actuate the Display DTC function by performing the following:
- If not done so previously, turn the blower control on.
- Press the A/C mode switch down, turn the blower control to off, wait 3 seconds and then release the A/C mode switch.

NOTE:
- The A/C status indicator displays active DTCs when the EBL status indictor is not illuminated and stored DTCs when the EBL status indicator is illuminated.
- If multiple DTCs are active, diagnose those that relate to a short circuit first.

Q: Is the A/C status indicator flashing DTCs?

YES: Diagnose and repair the DTC(s). Refer to HVAC related symptoms.
NO: As necessary, either Go To 4 or Perform BODY VERIFICATION TEST - VER 1. Body Verification Test

4. ACTUATOR CALIBRATION TEST
Actuate the Actuator Calibration function by performing the following:
- If not done so previously, turn the ignition on.
- Turn the blower control to off.
- Press the EBL mode switch down for 5 seconds and then release it.
- Wait approximately 90 seconds for the calibration process to run to completion before proceeding.

Turn the ignition off, wait 10 seconds, and turn the ignition on.
Actuate the Display DTC function by performing the following:
- Turn the blower control on.
- Press the A/C mode switch down, turn the blower control to off, wait 3 seconds and then release the A/C mode switch.

NOTE: The A/C status indicator displays active DTCs when the EBL status indictor is not illuminated and stored DTCs when the EBL status indicator is illuminated.

Q: Is the A/C status indicator flashing DTCs?

YES: Diagnose and repair the DTC(s). Refer to HVAC related symptoms.
NO: No problem found. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test