CPU Cooler

Compatibility
Compatibility is the most important thing to look out for when buying any PC parts. You need a cooler compatible with your processor, case, and motherboard. It's a good idea to familiarize yourself with sockets and other motherboard parts before you proceed. Different motherboards/CPU combos will have different sockets depending on the generation.
Fortunately, most CPU coolers are compatible across a wide generation of CPU sockets, both Intel and AMD. Just make sure you're buying a relatively modern cooler that supports your motherboard socket.
You'll also want to look out for the size. Certain air coolers can be too tall or bulky for smaller ITX cases and motherboards. Similarly, if you're buying a liquid cooler, make sure your case has enough space to install the radiator.

Air Cooling vs. Liquid Cooling
There are two different types of CPU coolers: traditional air coolers and liquid coolers. Air coolers are what you're most likely more familiar with. They have heat pipes that connect to the baseplate that sits on top of the CPU. These pipes carry the heat away from the processor and move it toward the heat sink and fan, which dissipates the heat into the air.
A liquid or AIO (all-in-one) cooler has pipes that carry water or coolant to the baseplate. The liquid removes the heat from the CPU and moves it to a radiator with attached fans. This radiator cools the hot liquid with the help of the fans, and the cooled liquid returns to the CPU to repeat the process.
In most cases, AIOs are better. They perform better because of the liquid cooling, and some people prefer how an AIO looks compared to traditional air coolers. However, air coolers are simpler and easier to install. They're also more reliable in the long term because of fewer moving parts.

Cooling Performance
You can get a pretty good idea of a CPU cooler's performance by looking at its TDP (Thermal Design Power) rating. TDP will help you determine how much heat your CPU will generate at maximum load. For example, a CPU with a TDP of 150W or higher will need a beefy CPU cooler rated to handle that power output.
Various factors, such as fan speed, pump speed, and heat sink density, can affect the overall cooling performance. It's also important to remember that just because a cooler looks good or has RGB lighting does not mean it also has good performance. That's not to say a cooler can't have all three, but you should always check reviews to see the expected performance.

Design and Aesthetics
Some people only care about performance, while others are all about aesthetics. However, it's fair to say that you'll likely prefer to have a balance between the two when building your PC. Performance should be the priority, but that doesn't mean a CPU cooler has to look ugly. If you don't like the look of traditional air coolers, feel free to splurge on a fancy AIO.
Liquid coolers now have fantastic RGB lighting, OLED displays on top of the pump, and high-quality backlit fans. Even modern air coolers offer various flashy designs and RGB lighting. If you want a specific color theme in your build, plenty of coolers come in black, white, and even pink.

Acoustics
Some air coolers will have high RPM fans that deliver excellent performance. However, they tend to get pretty loud because of the higher speed. If you care about acoustics, you can set a custom fan curve that's less aggressive and makes less noise. You can also just as easily swap out the fan for something quieter.

Installation
For first-time PC builders, installing a CPU cooler can be a bit daunting. You need to align the cold plate of the cooler perfectly with the CPU, make sure you have the right amount of thermal paste applied, and screwing the cooler into the motherboard is not a fun time. Still, you can get through it pretty easily if you know what you're doing. If you are a bit scared of the process, you can get coolers that have an easier installation.

Heat Sink: This is a metal component that absorbs heat generated by the CPU. It is designed with fins and heat pipes to maximize heat dissipation.

Heat Pipes: These are hollow pipes filled with a heat-conductive fluid. They transfer heat from the CPU to the heat sink, where it is dissipated through the fins.

Fan: The fan is responsible for blowing air over the heat sink, accelerating heat dissipation. It can be connected directly to the heat sink or mounted separately.

Thermal Paste: This is a conductive material applied between the CPU and heat sink to improve heat transfer. It fills in microscopic imperfections, enhancing thermal conductivity.

Mounting Brackets: These brackets secure the CPU cooler to the motherboard. They ensure proper alignment and contact between the CPU and heat sink.

Backplate: The backplate provides additional stability and support for the CPU cooler.

Control Circuitry: Some CPU coolers feature control circuitry that regulates fan speed based on temperature, optimizing cooling performance.

Step 1: Check if your cooler comes with a mounting backplate, or if it's designed to attach directly to a pair of retention clips around the motherboard's CPU socket. Most modern CPU coolers, including some stock coolers like AMD's Wraith Stealth, use backplates – if yours does, and your motherboard includes these retention clips, use a screwdriver to remove them.

Step 2: Assemble the cooler's backplate; this is what the main cooler will hold onto once it's installed. The backplate will likely need to be adjusted according to the motherboard socket type, but you should end up with four screws (or raised screw holes) that align with the four pre-cut holes around the motherboard socket. Press the backplate against the rear of the socket so that its protusions end up poking through to the other side, then lay the motherboard flat.

Step 3: It's time to apply thermal paste to the CPU, but what's the best way of actually doing so? Some say you should drop a dollop on the chip than use a piece of card or plastic to spread it over the CPU, like butter on toast. Others say to draw an X pattern with two thin lines of paste. I think, to get a consistent, fool-proof layer, you should squeeze a blob onto the chip and use the weight of the cooler itself to spread the paste nice and evenly. For now, just add that blob onto the middle of your processor.

Step 4: Here's where the installation process really diverges, depending on the cooler. Some coolers have four spring screws that go directly into the screw holes on the backplate; others may have metal loops that hook onto the aforementioned retention clips. For both of these types, just line them up, carefully push down on the cooler so that it spreads the thermal paste out from the centre, then secure it to the respective mounting mechanism. If your cooler has the four screws, turn them only partially, one at a time, repeating until they're all fully tight – this makes sure pressure is applied to the thermal paste more evenly.

Step 5: By this point you should have a fully mounted CPU cooler with, presumably, a suitably spread-out layer of paste between it and the CPU. All that's left to do is connect the fan to the motherboard, so grab the fan's cable and plug it into the 4-pin CPU_FAN header on the mobo. This is usually found along the board's top edge, or next to the CPU socket further down.

A malfunctioning CPU cooler can lead to various issues, including increased CPU temperatures, system instability, and potential damage to your computer's components. It's crucial to be able to detect signs of a CPU cooler malfunction early on to prevent any further damage.

Unusual Noises from the Cooler
One of the first indicators of a CPU cooler problem is the presence of unusual noises. A normally functioning cooler should operate quietly, with only a faint hum from the fan or pump. However, if you notice loud grinding, buzzing, or rattling sounds coming from your CPU cooler, it could be a sign of a malfunctioning fan or a problem with the pump. These noises might indicate that the fan is rubbing against something, or the bearings are worn out, affecting its performance.

Increased CPU Temperatures
Monitoring the temperature of your CPU is crucial to ensure its optimal performance and prevent overheating. If you notice a significant increase in CPU temperatures during regular usage or under heavy load, it could be a red flag for a malfunctioning CPU cooler. Higher temperatures than usual indicate that the cooler is not efficiently dissipating heat, potentially due to a faulty fan, clogged fins, or inadequate contact between the cooler and the CPU.

PC Shutdowns or Reboots
Frequent unexpected shutdowns or reboots are another warning sign that your CPU cooler may be malfunctioning. When a CPU reaches critical temperatures, the computer's built-in safety mechanisms can initiate an automatic shutdown or reboot to prevent damage. If your PC shuts down or restarts frequently, particularly during demanding tasks, it's essential to investigate the possibility of a faulty CPU cooler as a potential cause.

Inconsistent Fan Speeds
If you have a CPU cooler with adjustable fan speeds, monitor the fan's behavior. A malfunctioning cooler may exhibit inconsistent or irregular fan speeds. The fan may spin erratically or not reach the expected speeds, even under heavy loads. Inconsistent fan speeds can be an indication of a faulty fan controller or a problem with the cooling system's overall functionality.

Visual Inspection
Performing a visual inspection of your CPU cooler can also help you detect signs of malfunction. Look for any visible damage to the cooler, such as broken or bent fan blades, loose connections, or leaks in liquid cooling systems. Additionally, check for excessive dust or debris buildup on the cooler, as this can hinder proper airflow and cooling efficiency.