Circuit Description
The HVAC control module monitors the air conditioning (A/C) refrigerant charge using a refrigerant small leak detection algorithm. The algorithm monitors certain inputs and compares those inputs to pre calibrated normal values. Changes in the A/C refrigerant pressure effect the parameters that the algorithm monitors. When the A/C system has lost over 50 percent of its Freon charge, the refrigerant small leak detection algorithm may be effected enough to set the DTC. When the refrigerant small leak detection algorithm sets a code, the HVAC control module will not allow the A/C compressor clutch to engage except in defrost mode. This is done to protect the compressor. If a leak is found and fixed, the A/C system will still be disabled until the DTC is cleared.
Conditions for Running the DTC
| • | The engine is running. |
| • | The A/C is requested. |
Conditions for Setting the DTC
B0157
| • | The A/C refrigerant system has lost more than 50 percent of its Freon charge. |
| • | The refrigerant small leak detection counter triggers 3 times within 50 ignition cycles. |
Action Taken When the DTC Sets
| • | The HVAC control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The HVAC control module disables the A/C compressor clutch, except in defrost mode. |
| • | The driver information center will display SERVICE A/C SYSTEM. |
| • | The A/C OFF segment will illuminate on the HVAC control module. |
Conditions for Clearing the DTC
Use a scan tool in order to clear the DTC.
Diagnostic Aids
| Important: All DTCs that are set other than the B0157 must be diagnosed first. |
| • | If the A/C compressor clutch engages when the mode switch is in any other position than defrost and the DTC B0157 is set, the B0157 code has not detected 3 faults within 50 ignition cycles. The first and second time the algorithm recognizes A/C change to be below normal operating range, the B0157 sets as current but will not disengage the A/C pressure clutch. The third time the algorithm recognizes A/C pressure to be below normal operating range, the B0157 is set to current and the A/C compressor clutch will be disabled until the code is cleared with the scan tool. |
| • | Verify the system is at full charge. |
| • | Inspect the A/C system for leaks. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This test step determines if the clutch is disabled because of the B0157 algorithm or another condition that could cause the clutch to be disengaged and still set a B0157.
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This step tests for Freon leaks and mechanical problems in the A/C system.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | |||
1 | Did you perform the HVAC Diagnostic System Check? | Go to Step 2 | |
2 |
Does the air conditioning (A/C) compressor clutch engage in the vent position? | Go to Diagnostic aids | Go to Step 3 |
|
Important: All DTCs that are set other than the B0157 must be diagnosed first.
Does the A/C clutch engage in the defrost position? | Go to Step 4 | Go to Too Hot in Vehicle | |
Perform the A/C system performance test. Refer to Air Conditioning (A/C) System Performance Test in Heating, Ventilation and Air Conditioning. Did you find and correct the condition? | Go to Step 6 | Go to Step 5 | |
5 | Replace the HVAC control module. Refer to HVAC Control Module Replacement . | Go to Step 6 | -- |
6 |
Does the DTC reset? | Go to Step 2 | -- |
