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Automatic Air Conditioning

The content of this article and images reflects the changes identified in TSB- 10-55-003.


The A/C Indicator Flashes.

AUTO A/C









TECHNICAL DESCRIPTION (COMMENT)
If the A/C indicator flashes, inadequate refrigerant quantity, the ambient air temperature sensor circuit or the A/C pressure sensor circuit is suspected.


TROUBLESHOOTiNG HINTS
- Malfunction of the A/C pressure sensor
- Malfunction of the ambient air temperature sensor
- Malfunction of the A/C-ECU


DIAGNOSIS

Required Special Tools:
- MB991223: Test Harness Set
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)





STEP 1. Using scan tool MB991958, read the diagnostic trouble code

Check if an A/C-ECU DTC is set.
1. Connect scan too MB991958 to the data link connector.
2. Turn the igniton swtch to the "ON" position.
3. Check if the DTC is set.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the check result satisfactory?

YES: Go to Step 2.

NO: Refer to DIAGNOSTIC TROUBLE CODE CHART





STEP 2. Using scan tool MB991958 check data list.


To prevent damage to scan tool MB991958 always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
(1) Connect scan tool MB991958 to the data link connector.
(2) Assemble a manifold gauge onto the high pressure service valve.
(3) Turn ON the engine and then turn ON the air conditioner switch.
(4) Set scan tool MB991958 to the data reading mode for item 04: A/C pressure sensor.
Check that the refrigerant pressure matches the displayed value on the scan too.
(5) Turn the ignition switch to the "LOCK" (OFF) position.

Q:Is the sensor within the specified range?

YES: Go to Step 7.

NO: Go to Step 3.





STEP 3. Check A/C pressure sensor connector A-30 for loose, corroded or damaged terminals or terminals pushed back in the connector.

Q:
Is A/C pressure sensor connector A-30 in good condition?

YES: Go to Step 4.

NO: Repair or replace the connector. Refer Harness Connector Inspection. Check that the A/C works normally.








STEP 4. Check the A/C pressure sensor.
1. Assemble a gauge manifold on the high pressure service valve.
2. Disconnect the A/C pressure Sensor connector and connect special tool test harness MB991958 as shown in the illustration.
3. Turn ON the engine and then turn ON the A/C switch.





4. At this time check to see that the voltage of A/C pressure sensor terminal No. 2 reflects the specifications of the figure.

NOTE: The allowance shall be defined as greater than or equal to 5%.

Q: Is the A/C pressure sensor in good condition?

YES: Go to Step 5.

NO: Replace the A/C pressure sensor. Check that the A/C works normally.







STEP 5. Check A/C-ECU C-15 and C-16 for loose, corroded or damaged terminals or terminals pushed back in the connector.

Q: Are A/C-ECU C-15 and C-16 in good condition?

YES: Go to Step 6.

NO: Repar or replace the connector. Refer to Harness Connector Inspection. Check that the A/C works normally.





STEP 8. Check the wiring harness between A/C-ECU connector C-15 (terminal 12), C-16 (terminals 34 and 26) and A/C pressure sensor connector A-30 (terminals 3, 1 and 2).





NOTE:
Also check intermediate connector C-29 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If intermediate connector C-29 is damaged, repair or replace the connector as described in Harness Connector Inspection.

Q: Is the wiring harness between A/C-ECU connector C-15 (terminal 12), C-16 (terminals 34 and 26) and A/C pressure sensor connector A-30 (terminals 3, 1 and 2) in good condition?

YES: Go to Step 7.

NO: Repair the wiring harness. Check that the A/C works normally.





STEP 7. Check ambient air temperature sensor connector A-25 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is ambient air temperature sensor connector A-25 in good condition?

YES: Go to Step 8.

NO: Repair or replace the connector. Refer to Harness Connector Inspection. Check that the A/C works normally.






STEP 8. Check the ambient air temperature sensor.

(1) Disconnect ambient air temperature sensor connector A-25.

CAUTION: The ambient air temperature sensor should be checked without removing it. If the sensor is removed, it is no longer serviceable.





(2) Measure the resistance between the sensor terminals under at least two temperatures. The resistance values should meet the values shown.

NOTE: The temperature should be with in the shown range.

Q: Is the ambient air temperature sensor in good condition?

YES: Go to Step 9.

NO: Replace the ambient air temperature sensor. Check that the A/C works normally.





STEP 9. Check A/C-ECU connectors C-15 and C-16 for loose, corroded or damaged terminals or terminals pushed back in the connecter.

Q:
Are A/C-ECU connectors C-15 and C-16 in good condition?

YES: Go to Step 10.

NO: Repair or replace the connector. Refer to Harness Connector Inspection. Check that the A/C works normally.





STEP 10. Check the wiring harness between A/C-ECU connector C-15 (terminal 20), C-16 (terminal 23) and ambient air temperature sensor connector A-25 (terminals 1 and 2).





NOTE:
Also check intermediate connector C-23 and joint connector C-03 for loose, corroded, or damaged terminals or terminals pushed back in the connector. If intermediate connector C-23 orjoint connector C-03 is damaged, repair or replace the connector as described in Harness Connector Inspection.

Q: Is the wiring harness between A/C-ECU connector C-15 (terminal 2O), C-16 (terminal 23) and ambient air temperature sensor connector A-25 (terminals 1 and 2) in good condition?

YES : Then go to Step 11.

NO: Repair the wiring harness. Then go to Step 11.






STEP 11. Check the refrigerant level.
Use the refrigerant recovery station to remove all of the refrigerant and then calculate the amount of the refrigerant and charge it.

Q: Is the refrigerant level correct?

YES: Replace the A/C-ECU. Check that the A/C works normally.

NO: Correct the refrigerant level. Check that the A/C works normally.