Checking Air Conditioning (A/C) Compressor Control

Checking air conditioning (A/C) compressor control

Check, cables and components

Note! This test is designed for the electrical circuit between ECC/MCC control module and engine control module (ECM) via the low pressure switch.

Check the connectors on the ECC/MCC control module, low pressure switch and engine control module (ECM) for contact resistance and oxidation according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault.
Check signal cable between ECC control module #A3 (MCC control module #B22) and engine control module (ECM) for an open-circuit according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault.
At normal system pressure in the air conditioning (A/C) system the low pressure switch should be closed (approximately 0 ohm). If the pressure is too low the switch is open (infinite resistance).
Remedy as necessary.

Other information:
- To access/replace the ECC control module, refer to Replacing ECC control module Removal and Replacement.
- To access/replace the MCC control module, refer to Replacing or adjusting control cables / mechanical rear section and control panel / front section (Manual climate control / STANDARD) Service and Repair.
- Connection of breakout box to ECC control module, refer to Connection of breakout box ECC Connection of Breakout Box ECC.
- Connection of breakout box to MCC control module, refer to Connection of breakout box MCC Connection of Breakout Box MCC.
- Voltage on the cable should be 0-2 V below air conditioning battery voltage when the control module demands air conditioning (A/C), approximately 0 V when air conditioning (A/C) is not demanded. For other signals, see Signal specification ECC Signal Specification ECC and Signal descriptions MCC Signal Descriptions MCC.

















Was any fault detected?

Yes - FAULT FOUND

No - No Fault Found

-------------------------------------------------