3. A/C, cars with diesel engines: Notes

Fig 1: Identifying Bus Function Chains - A/C (Cars With Diesel Engine - 1 Of 2)

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Identifying Bus Function Chains - A/C (Cars With Diesel Engine 2 Of 2)

Courtesy of SAAB-SCANIA OF AMERICA, INC.

A number of conditions must be fulfilled for the A/C relay to be grounded and the A/C compressor's electromagnetic clutch to operate.

In AUTO mode, the ACC unit will request the DICE for A/C engagement if:

• The outside temperature (information via bus from SID) is above 0°C.

DICE then sends the A/C request if the following conditions are fulfilled:

1. Coolant temperature (information via the bus from MIU/engine control module) is below 125°C.
2. Refrigerant pressure (own sensor) on the high-pressure side is between 2 and 27 bar.
3. Temperature in the evaporator (own sensor) must be above 4.5°C.

In cars with diesel engines, the A/C request is used directly by the engine control module, which activates the A/C relay as soon as the engine has started. Diesel engine control modules also have the condition that the coolant temperature must be below 120°C.

In practice, this means that the condition for the engine coolant temperature in DICE (point 1) is meaningless on cars with diesel engines.