The 120mm all-in-one cooler in my six-year-old prebuilt has started acting up. The PC shows a CPU fan error during boot, and the pump RPM occasionally drops, although temperatures still look normal. I'm considering replacing the entire cooler and am unsure whether to buy another 120mm AIO or switch to an air cooler. The CPU is an Intel Core i7-9700K. I've never worked inside this PC before, so I'm a little nervous about the installation. I can provide pictures of the case if clearance information is needed.
3 Answers
A decent air cooler is usually a better choice than a 120mm AIO and can often be found for under $40. It’s simpler, has fewer parts that can fail, and avoids dealing with a pump. The main thing to check first is the case model or the maximum CPU-cooler height so you know the replacement will fit.
Air cooling would be my preference here. Replacing a fan or even the whole cooler later is generally easier than troubleshooting a pump, radiator, and extra cables. A dual-tower cooler offers plenty of performance, while a smaller single-tower model may be a better fit if the prebuilt case is cramped.
For an i7-9700K, a quality tower air cooler should work well, assuming you aren’t running an aggressive overclock. Models such as the Thermalright Assassin X or Peerless Assassin are popular budget options, but confirm the cooler’s height and mounting support for your motherboard before buying. Installation is mostly removing the old pump block, cleaning the CPU, applying thermal paste, and securing the new cooler and fan.

The case dimensions matter more than the cooler’s advertised performance. Check the manufacturer’s CPU-cooler clearance and also make sure the cooler doesn’t interfere with the RAM or side panel.