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So the A/C in my LR4 was never quite right since I bought it in fall. It worked, but on hotter days it barely cooled at all, but I never got round to it because I had other priorities.

As fall turned to winter, I didn't need max performance; as long as the fan worked all was well. Then summer happened.

Given the unique circumstances the world found itself this spring, I didn't really use the car much, except for short jaunts to and from the supermarket for essentials. It did cool, but barely, and given that I had no other passengers during my outings I thought nothing of it.

Then a couple of weeks ago on an especially hot weekend it felt like the A/C was giving nothing back. So I took it in to a mechanic who had a fancy machine that extracts, recycles and refills Freon (R-134a), along with vacuum testing capabilities.

What we found was a little astonishing. The car is designed to have 900 g of Freon at full charge, but the machine extracted just 172 g. This by itself isn't so remarkable; I reasoned that there must be a leak in the system. What surprised me was that the system sustained 15 (or was it 20?) in Hg vacuum for about 10 minutes, suggesting that there were no major or obvious leaks.

The mechanic went ahead and charged up the system to 900 g (along with 10 ml compressor oil), and the A/C works like a champ now. But I do wonder, how on earth was the A/C able to give me any cooling with just 20-30% charge before it dropped off precipitously?

I know that A/C performance can be quite sensitive to the amount of refrigerant present in the system, so assuming that there is a very slow leak present in the system, I'm stumped as to how there could have been any cooling over the past months with 20-30% (even 50% if we're being generous) of what Land Rover says it should be.

I understand that weather is a factor here, but up until that very hot day two weeks ago it did give me some cooling, albeit very little, similar to how it was during fall season.

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In most systems, and I'm sure your LR4 is typical, there is a low pressure switch that will shut off the compressor after a minute or two if there is too little refrigerant in the system. After another minute or two it will cycle back on and the process repeats. This mode of operation doesn't provide much cooling and, as you noted, it seems to work for a while then stops.

Chances are that there is a leak and a a vacuum test doesn't always show the problem. The best approach is to add some UV dye to the system and then locate the leak using a UV light.

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  • Vacuum test is limited, UV dye test can even highlight micro leaks. – Numair Aidroos Jun 20 at 2:01

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