A vast number of heat pumps have been installed everywhere since the first oil crisis of 1973. Most of these heat pumps are fitted with a 4- way cycle inversion valve used either to change the pumps to summer mode (cooling) or to defrost the external unit in winter mode (heating).

The object of this chapter is to study the operation of the 4-way cycle inversion valve (4WV) fitted to the majority of standard air-air heat pumps, as well as those defrost systems that use cycle inversion (see page 433). This should allow effective remedial action to be taken in the face of the commonest faults...

EXERCISE : In the middle of winter, an engineer needs to replace the 4WV of the installation opposite.

After recovering the refrigerant from the system and removing the defective 4WV, the engineer asks himself the following question:

With the low external and internal temperatures, the control system will try to start the heat pump in "heating" mode.

Therefore, before fitting the new 4WV, would it be better to bring the slide to the right, or does it matter which side it's on?

To help you, we've reproduced a diagram marked on the solenoid.

(Solution : Refrepair Manual pages 325 to 337)