3. A/C: Notes

Fig 1: Identifying Bus Function Chains (A/C)

Courtesy of SAAB-SCANIA OF AMERICA, INC.

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

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

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

DICE then requests that the TRIONIC control module ground the A/C relay if the following conditions are fulfilled:

1. Coolant temperature (information via bus from the Trionic) is below 125°C.
2. Refrigerant pressure (own sensor) on the high-pressure side is between 2 and 27 bar.
3. The temperature in the evaporator (own sensor) must fulfil the following conditions:
   1. 3.a. If the temperature in the evaporator is above 3°C, DICE sends via the bus a request to the Trionic control module for A/C engagement.
   2. 3.b. If the temperature in the evaporator is below 0°C, the A/C compressor can only be engaged if the conditions in points 4 and 5 are satisfied.
4. The outside temperature (information via bus from SID) must be above 25°C.
5. One of the following conditions must also be met:
   1. 5.a. The engine must not have been running for more than 30 minutes (information via bus from the Trioinic control module).
   2. 5.b. Vehicle speed is below 5 km/h (information via bus from MIU).

The Trionic will then activate the compressor relay.