Injection strategy - air conditioning

I - INJECTION ECU - AIR CONDITIONING ECU LINK

A/C control is shared between several control units.

The injection ECU is responsible for:

• manage the cooling demand based on passenger compartment controls and the refrigerant circuit pressure value,
• determine the power absorbed by the A/C compressor from the refrigerant circuit pressure value,
• authorise fan unit operation based on vehicle speed and refrigerant circuit pressure,
• enabling or disabling compressor clutch engagement.

When air conditioning is switched on, the A/C control panel requests permission for the A/C compressor to operate.

The injection ECU authorises or prohibits:

• operation of the A/C compressor,
• operation of the fan unit,
• an increased idle speed.

This speed depends on the power absorbed by the compressor:

• 850 rpm (K4J and K4M engines),
• 900 rpm (F4R engine).

Fan unit and compressor control requests are sent from the injection ECU over the multiplexed network. The request depends on the air conditioning, engine coolant temperature and vehicle speed.

The fan unit and compressor are powered through the protection and switching unit.

Information used for this function is exchanged over the multiplexed network:

• pin A A4 multiplexed link "CAN HIGH",
• pin A A3 multiplexed link "CAN LOW".

The injection ECU receives the refrigerant pressure sensor information on the following pins:

• B J3 refrigerant pressure sensor signal,
• B J2 refrigerant pressure sensor +5 volt supply,
• B K2 refrigerant pressure sensor earth.

The compressor is a variable displacement type.

WARNING

The value of parameter PR044 "A/C compressor absorbed power" is never equal to 0, whatever the compressor state. The minimum value read is approximately 250 to 300 watts.

II - COMPRESSOR ENGAGEMENT STRATEGY

In certain operating phases, the injection ECU prohibits operation of the A/C compressor.

K4J

1 - Hill start performance recovery strategy

To assist hill starts, operation of the A/C compressor is prohibited for a 10-second timer.

2 - Maximum speed protection strategy

The compressor does not operate if:

• instantaneous engine speed is greater than 6688 rpm,
• steady engine speed is greater than 6112 rpm for more than 10 seconds.

3 - Thermal protection strategy

The compressor does not operate if the coolant temperature is above 119 C at high speed and high load.

Entry conditions:

• engine speed above 6496 rpm,
• " and " manifold pressure at 1046 mbar.

Exit conditions:

• engine speed below 6496 rpm,
• " and " coolant temperature below 119 C,
• " and " manifold pressure below 1046 mbar.

K4M

4 - Engine start strategy

Compressor operation is prohibited for 10 seconds after engine start.

5 - Performance recovery strategy

Compressor operation is prohibited for a 5-second timer.

Entry conditions:

• throttle fully open,
• " and " engine speed below 2016 rpm,
• " and " vehicle speed below 16 km/h.

Exit conditions:

• throttle not fully open,
• " or " 5-second timer elapsed,
• " or " engine speed greater than or equal to 2048 rpm,
• " or " vehicle speed above 26 km/h.

6 - Hill start performance recovery strategy

To assist hill starts, under certain load and engine operating conditions, operation of the A/C compressor is prohibited for 5 seconds.

7 - Maximum speed protection strategy

The A/C compressor does not operate if engine speed is greater than 6496 rpm.

8 - Thermal protection strategy

The A/C compressor does not operate if the coolant temperature is above 119 C at high speed and high load.

F4R

9 - Hill start performance recovery strategy

To assist hill starts, operation of the A/C compressor is prohibited for 20 seconds.

10 - Maximum speed protection strategy

The A/C compressor is prohibited if:

• instantaneous engine speed is greater than 6300 rpm,
• steady engine speed is greater than 5760 rpm for more than 10 seconds.

11 - Thermal protection strategy

The A/C compressor is prohibited if the coolant temperature is above 115 C at high speed and high load.

Entry conditions:

• engine speed above 4512 rpm,
• " and " manifold pressure below 700 mbar.

Exit conditions:

• 10-second timer elapsed,
• " and " certain conditions of the engine coolant temperature management (GCTE) function.