900 S Convertible L4-2290cc 2.3L DOHC (1996)
The A/C compressor is always on in the Auto mode of operation. When the A/C is on, the ACC control module sends Batt+ to ICE.
If the coolant temperature does not exceed +126 °C, ICE sends Batt+ to the engine control module via the anti-freeze thermostat.
The engine control module compensates idling speed and after a short delay sends ground to the A/C relay via the low-pressure and high-pressure
monitor.
When the A/C relay operates, the circuit to the magnetic coupling is closed.
The engine control module breaks the circuit to the A/C relay during heavy acceleration.
In the AUTO mode of operation during normal driving conditions and when the outside temperature is above about +1 °C, the anti-freeze
thermostat decides whether the A/C compressor is to run or not. The reason why the A/C compressor runs even when cooling is not required is
because the evaporator dries incoming moist air and so prevents the windshield from misting up in damp weather. The A/C compressor can be shut
off with the ECON button.
Compressor Oil
PAG oil (poly alcylene glycol), a fully synthetic oil of glycol type, is used in the A/C system.
PAG oil is very hygroscopic, i.e. it absorbs moisture from the air very easily in the same way as brake fluid does. Water is bound chemically in the
oil and cannot be removed by vacuum pumping. It is therefore important that the oil is stored in closed containers and that it is not exposed to the
air for more than very short periods. The oil is supplied in tubes of 20 ml to minimize the risk of left-over oil being stored for the next time it is
needed.
