A refrigeration cycle moves heat from a cold space to the outside using a refrigerant that changes state. To explain it, say what happens to the refrigerant in each of the four main parts.
This lesson belongs to the wider SPM subjects and learning resources section. The table below is original and simplified, and it covers the concept only.
What is the cycle doing?
Heat naturally flows from hot to cold. The cycle pushes heat the other way by making the refrigerant colder than the space inside, then hotter than the air outside.
That is why the compressor and the expansion device matter: they set the pressure, and pressure sets the temperature.
Worked example: a four-part cycle
An original diagram shows four labelled parts in a loop: compressor, condenser, expansion device and evaporator.
| Part | State of refrigerant | What happens |
|---|---|---|
| Compressor | Vapour in, hot high-pressure vapour out | Pressure and temperature rise |
| Condenser | Hot vapour in, liquid out | Heat is released to the outside and the vapour condenses |
| Expansion device | High-pressure liquid in, cold low-pressure mixture out | Pressure drops, so the refrigerant becomes cold |
| Evaporator | Cold mixture in, vapour out | Heat is absorbed from the space and the liquid evaporates |
A model explanation: “In the evaporator the cold refrigerant absorbs heat from inside the cabinet and changes to vapour, which cools the cabinet. The compressor then raises the pressure of that vapour so the condenser can release the heat outside.”
The mistake that loses marks
A weak answer says: “The compressor, condenser, expansion device and evaporator work together to make the fridge cold.” All four parts are named and none is explained.
A stronger answer says what changes in each part: pressure, temperature or state. If your sentence has no change in it, it only names the part.
Reading the diagram as a loop
The cycle has no start or end, so pick a point and follow the arrows. A good point is the evaporator outlet, where the refrigerant is a vapour ready to be compressed.
From there the order is compressor, condenser, expansion device, evaporator. Saying the order aloud and naming the change at each part is an effective way to memorise it.
Keeping answers conceptual
Refrigerant handling is regulated and can be dangerous, so it is taught only in the school workshop with supervision. Written answers explain the cycle and the function of parts.
If a question describes a cabinet that does not cool, a sound answer names which stage might not be doing its job, for example a blocked expansion device giving too little cold refrigerant, and leaves the fix to trained staff.
Check yourself
Which part releases heat to the outside, and what happens to the refrigerant there? Answer in two sentences.
Answer
The condenser releases heat to the outside. The hot, high-pressure vapour loses heat there, so it condenses into a liquid.
A careful answer adds that the heat released includes the heat absorbed in the evaporator plus the work added by the compressor.
What to study next
Test your explanations with the structured-answer self-review tool. A similar follow-the-change habit is used in tracing a conceptual domestic circuit.
For a teacher to go through more cycle diagrams with you, see online one-to-one Servicing Refrigeration and Air Conditioning Equipment tuition or the one-hour trial class (from RM50). Equipment work stays with your school.