Stick with it Eric, you’ll get there!
I hope this little article helps with the basic fundamentals – re-read it when you need to, and after a few times it will sink in forever!

Hi Paul, thanks for your thoughts!
With regard to your question there is no single fixed maximum temperature decrease — it depends on the design and operating conditions of the system.
The minimum evaporator temperature and the maximum condenser temperature are constrained by certain factors though.

The refrigerant cannot condense above its critical temperature, though in practical everyday terms, HVAC system condensing temperatures are usually much lower than their critical temperatures – (often 35–55°C | 95-131°F), depending on ambient conditions and system design. As temperature & pressure are directly linked in the refrigeration cycle, higher temperatures result in higher pressures, and these higher pressures often cause safety devices such as high pressure cut out switches to stop the compressor from working. Necessary both from a physical safety aspect and the protection of the compressor from damage.

So as an example, while the absolute maximum condensing temperature for the common US refrigerant R22 is 96°C | 205°F, in practice systems are designed to run far below that for efficiency and safety.

Similarly, their are limitations to the evaporator part of the system, and a system set too low can regularly ice up causing restricted airflow through the evaporator fins. This can prevent the refrigerant from boiling off from a liquid to a gas, meaning liquid refrigerant makes its way back to the compressor, which can cause serious damage. Therefore, there are also protection devices within the system that will shut it down to prevent this.

Let’s say your typical air conditioning evaporator temperature is 4°C | 39°F and the condensing temperature is 48°C | 118°F, that’s a refrigeration effect difference in temperature of 44°C | 111°F. A statistic or differential that engineers would call Delta Temperature or ΔT. A single-stage vapor-compression cycle is usually limited to about 50–70°C | 122-158°F total temperature drop.
To achieve larger drops (100–200°C | 212-392°F), multi-stage or cascade refrigeration cycles are required.

So in relation to your A/C’s struggling to keep up, if you are evaporator is blowing out at 4°C | 39°F and you have 38°C | 100°F outside ambient temperature, you’re going to have a condensing temperature up around 54°C | 129°F. That’s a ΔT of 50°C | 122°F, and you can see you are getting towards the upper limits of what’s practical & safely achievable in the single stage vapour compression cycle.

Kind words, thanks for sharing Kevin!
Delighted our little article has helped another interested mind in understanding the refrigeration cycle today.

Hi Dan, thanks for your question – a good one!

In this article & diagrams, we’ve tried to keep things as simple as possible to help people with no knowledge of the refrigeration cycle understand the basic principles.
In reality there a lots of different types of refrigeration & air conditioning systems, components, configurations & uses.

For instance, most air conditioning systems will have the compressor, condenser & meeting device all contained together in the outdoor unit. The indoor unit (evaporator) could be as far as 70+ metres away from the condenser. In this case the pipe work containing the refrigerant between the metering device & the evaporator is often referred to as an EXPANSION line, rather than a LIQUID line. The refrigerant in the expansion line has already gone through the expansion (metering) device and while there is still liquid present, it is essentially a vapour with both liquid & gas present. The refrigerant is still confined within the relatively narrow pipe work though, so can’t expand further in to gas until it reaches the evaporating unit where it can expand within the additional pipe network in the evaporator coils, and absorb the heat from the room being cooled, turning the refrigerant in to a gas before it returns to the compressor.

We term the states of the refrigerant as ‘Liquid’, ‘Vapour’ & Gas, but obviously as a refrigerant transitions through the vapour stage either evaporating or condensing, there will be differing states of the vapour from almost entirely liquid to almost entirely gas. Before a refrigerant reaches the evaporator, it will be a vapour, but it will be mostly liquid.

Another way to think of it is to imagine a new bottle of refrigerant. There’s no air in the bottle – when the bottle is filled it is vacuumed first to remove all the air, but when you pick up a new bottle of refrigerant it’s not 100% full of liquid. You can feel the liquid sloshing around inside when you shake the bottle. Inside the bottle there will be liquid, vapour and possibly gas too. The refrigerant in all 3 states within the same vessel or environment – But generally we’d refer to it as being liquid.

In terms of refrigeration systems, the metering device is usually very close to the evaporator unit – often inside it, and can be quite literally centimetres away from the coil.
Similar to an air conditioning system like described above, the refrigerant exiting the metering device will be a vapour, but mostly liquid, until it passes through a distribution device – sometimes called a SPIDER because it has lots of legs, where it then enters several different loops of the evaporator coil, and the real expansion starts, allowing the liquid refrigerant to further vaporise and finally turn in to a gas.