Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Functional description
Stepless power control is possible in the air conditioning compressor. Within the A/C compressor, the delivery volume and thus the pressure in the refrigerant circuit is generated by pistons. The piston stroke is controlled by a swash plate. The swash plate is adjusted with the help of this movement:
- Minimum displacement (below 3 %)
The electrical control valve is open when de-energized. In this position, the compressor capacity drops to nearly 0 %, in order to reduce the fuel consumption. During a switched on Air conditioning, the minimal compressor capacity lies between 0 % and 3 %, which helps maintain the inner lubrication. A pressure build-up is also enabled, even if liquid refrigerant has accumulated in the air conditioning compressor (physically related).
- Maximum displacement (100 %)
- Control range (0 % to 100 %)
The electric control valve on the A/C compressor influences the balance of forces on the swash plate and thus the adjustment of the displacement.
F0x, F1x, F25 and F26: The junction box electronics (JBE) controls the control valve with a clocked voltage. The IHKA control unit prompts the activation.
F15, F16: The Body Domain Controller (BDC) controls the control valve with a pulsed voltage. The IHKA control unit prompts the activation.
F2x, F3x: The front electronic module (FEM) controls the control valve using a pulsed voltage. The IHKA control unit prompts the activation.
For the purpose of load reduction, only the cooling power that is directly needed is generated. The rules and criterion for switching it on/off are:
- Speed of the air conditioning compressor (engine speed)
- Load torque of the air conditioning compressor (CAN message from the IHKA control unit to the engine control unit)
- Limit of torque (CAN message from the engine control unit to the IHKA control unit) restriction of the load torque of the air conditioning compressor during kick-down position or at a higher coolant temperature.
- Limit of the refrigerant pressure
- Ambient temperature
The following graphic shows an example of an air conditioning compressor.
| Item | Explanation |
|---|---|
| 1 | Electrical control valve with two-pin plug connection |
| 2 | Refrigerant line (pressure line) connection |
| 3 | 1-pin plug connection from the magnetic coupling |
| 4 | Magnetic coupling and belt pulley |
| 5 | Refrigerant line (intake pipe) connection |
| 6 | 3-pin plug connection (connection to vehicle network) |
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.