Evaporator temperature sensor

The gas outlet control system is governed by an ECU. This acts on the compressor solenoid according to evaporator temperature, which is recorded using an NTC cursor (96 - see figure on next page).

When button (99) is pressed to activate the air conditioner, the ECU is supplied with 12V positive voltage to terminal (1). Under these conditions, the ECU activates the gas flow control solenoid (94B) so that the compressor is set to operate with an output of 17%.

Simultaneously, a positive signal is sent to terminal (8) of fuel injection control unit (85), which adjusts engine idle speed. After a delay of several milliseconds, relay (E) for activation of compressor coupling (94A) is excited.

During air conditioner operation, if evaporator temperature exceeds 5 °C, the ECU sets the compressor to maximum output (100 %).

If evaporation temperature reaches a level of between 3 - 4 °C, the ECU excites the flow control solenoid (94B) and output is reduced to 17% of the total.

The amount of gas entering the evaporator is therefore reduced and the cooling effect consequently falls.

If evaporator temperature reaches values of less than 3 °C, the ECU releases relay (E) and thus consequently the compressor coupling.

The compressor coupling is released when the accelerator pedal is pushed to the floor and when the engine temperature reaches 107°C to avoid further overheating. These operations are carried out by the electronic injection ECU (85).

The ECU always sets the compressor to operate at 17% of the total output whenever it is activated in order to reduce engine load. This situation is maintained for a minimum of 4 seconds. After this, ECU (95) decides whether to set the compressor to maximum output or not, as described previously, on the basis of evaporator temperature. The compressor ECU (95) is informed that the air conditioner has been activated via a 12 V signal to terminal (1). When the compressor is activated by the fuel injection control unit, the ECU is informed via terminal (2) which is connected in parallel to the coupling via auxiliary control unit (91).

NOTE The connections of electronic injection ECU (85) shown in the diagram refer to the version 1242 SPI and MPI.

Evaporator temperature sensor

Temperature sensor (96) is an NTC resistor and positioned close to the evaporator outlet pipe. It is not accessible from the outside.

In the case of Service operations that involve evaporator removal/refitting, it is important NOT TO MOVE THE SENSOR FROM ITS ORIGINAL POSITION, because the different temperature levels read by a differently positioned sensor could lead to incorrect compressor output control.

Sensor reference values are: