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I have a 2002 Nissan Almera 1.8L AT which seems to have a CSV613 A/C compressor, which is a variable displacement compressor.

I understand that there is a swash plate which somehow moves around to change the compressor displacement and thus the amount of cooling, and this is as opposed to other systems which cycle the clutch. But I only see a single electrical connector which I assume is for the clutch coil, and can't understand how the ECU would control the swash plate to change the displacement.

Can anyone explain how these things work and are controlled?

  • there a lots of sources for this type of mechanism : hydraulic pumps etc – Solar Mike May 21 '17 at 7:23
  • Maybe the system control is based on the expansion valve (throttle) in the A/C system and the compressor adjusts to the load. – Solar Mike May 21 '17 at 8:47
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Since this variable displacement compressor features only a clutch coil cable and no solenoid valve cables, it's "internally controlled", that is, it doesn't require any control at all from an external source to operate (this kind of variable displacement compressor necessarily requires a clutch, otherwise the AC system would basically be always on; instead, the CSE613, since it's an externally controlled compressor, that is, the swash plate angle is controlled by a solenoid valve, in turn controlled by a signal fed by a control unit, doesn't require one).

In an internally controlled variable displacement compressor, the wobble/swash plate angle (and, therefore, the pistons stroke) is determined by the evaporator's temperature and, hence, TXV opening degree and suction pressure (therefore, a pressure switch on the suction line or an anti-icing sensor isn't required, unlike with a fixed displacement compressor).

There's a mechanical control valve inside the compressor, which senses the suction line pressure and begins acting on a pressure differential and therefore an equilibrium of forces inside the compressor once a certain suction line's pressure and therefore evaporator temperature is reached.

In layman's terms, when the suction line's pressure decreases, the swashplate angle decreases, until it reaches a minimum. When it increases, the angle begins increasing.

Basically, in a hot summer day, provided that the system is working properly and charged up to specs and that you have a clean cabin filter, you can see the compressor's internally controlled variable displacement mechanism in action with these experiments: if you keep the blower at the maximum speed (Or the automatic temperature control at minimum temperature, without setting the blower speed, so that the fan reaches maximum speed), you have all windows open and you have recirculation off, you should notice more load on the engine since the evaporator won't cool enough and therefore the compressor works to max capacity and moves all the refrigerant vapour it can around the system.

If, instead, you close all windows, keep the cabin's blower fan at minimum speed (and, if you have ATC, set the temperature to the minimum value and the ventilation to the minimum speed, so that the air won't be heated up by the heater matrix increasing the load on the evaporator; unlike with externally controlled compressors, internally controlled compressors always aim to reach a fixed evaporator's temperature, so air temperature can't be influenced by varying the amount of refrigerant pumped across the system) and turn recirculation on, you should immediately notice less engine load and therefore a faster engine reaction (since the decreasing evaporator temperature and, in turn, TXV opening, lowers the suction pressure down to the point that the swashplate angle reduces and the compressor begins destroking and pumping almost nothing through the system, until the system attains an equilibrium).

Forgot to add that unlike fixed displacement compressors, variable displacement compressors equipped with clutches should be always rotating and pumping (more or less as described, but always pumping something) as long as the HVAC system is switched on in the AC (or defrost, if the system is set to turn the AC compressor on in defrost mode) mode. If they don't, something is wrong within the system. In addition, the same behaviour regarding engine load with respect to evaporator's load can, to some extent, be noticed even with fixed displacement compressors. The difference between the two is that fixed displacement compressors should periodically disengage their clutches (they should do so whenever the minimum suction pressure value or evaporator's temperature is reached) and engage them again after some time (whenever the suction pressure or evaporator temperature increase again above the minimum threshold).

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