3. A/C, cars with the Trionic T7 engine management system: Notes

Fig 1: Identifying Bus Function Chains - A/C (Cars With Trionic T7 Engine)

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.

The DICE then requests the Trionic control module to ground the A/C relay if the following conditions are fulfilled:

1. The engine coolant temperature (bus information 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 meet the following conditions:
   1. 3.a. If the evaporator temperature is higher then 3°C, DICE will send an A/C engagement request via the bus to the Trionic control module.
   2. 3.b. If the evaporator temperature is below 0°, the A/C compressor can only be switched on if points 4 and 5 are fulfilled.
4. The outside temperature (bus information from SID) must be above 25°C.
5. One of the following conditions must also be met:
   1. 5.a. The engine must have been running for less than 30 minutes (bus information from the Trionic control module).
   2. 5.b. Vehicle speed is below 5 km/h (bus information from the MIU).

The Trionic T7 then activates the compressor relay.