Computers turn electrical power into heat, and that heat has a cost. When temperatures rise, performance can drop, parts can fail sooner, and systems become unstable. For the CompTIA A+ 220-1201 exam, Objective 3.5 focuses on how technicians control cooling to keep devices reliable.
This objective covers five areas you’re expected to recognize and explain: cooling basics, fans, heat sinks, thermal paste or pads, and liquid cooling. Each plays a specific role, from moving warm air out of a case to transferring heat off a CPU or GPU and into a larger surface that can shed it.
When cooling isn’t working, the symptoms are often obvious. You might see thermal throttling, sudden shutdowns or reboots, loud fans running at full speed, or a system that feels sluggish under load. Over time, excessive heat can shorten hardware life and increase the chance of intermittent faults.
This post breaks down what each cooling part does, where you’ll see it in real systems, and what to check during troubleshooting. The goal is clear: identify the cooling method in front of you, spot common failure points, and connect symptoms to likely causes.
How heat moves inside a PC, and what "good cooling" really means
Inside any computer, heat follows a simple path: it starts at the parts that use power, it spreads into nearby metal and air, and it leaves the system through vents. Your job as a technician is to help that path stay smooth. Good cooling does not mean “the fans are loud” or “the case feels cold.” It means heat transfers efficiently from the chip to a cooler surface (heat sink, heat pipe, radiator), and warm air exits the system without getting trapped or recycled.
It also means temperatures stay stable under load. A PC that boosts fast but then slows down is often cooling-limited, not CPU-limited. When you understand where heat comes from and how it should move, you can connect symptoms to the right fix, instead of guessing.
Common parts that run hot, and the symptoms you’ll see first
Most heat problems come from a small set of components. Each one tends to show trouble in a predictable way.
- CPU (desktop or laptop): The CPU can produce sharp heat spikes, especially during boosts. The first sign is often slow performance under load due to thermal throttling. You may also see sudden reboots or shutdowns when the system hits a thermal limit, plus fans that ramp up and stay high.
- GPU (discrete graphics card): GPUs dump a lot of heat into the case. When cooling is weak, you might see screen artifacting (odd colors, flicker, blocks), driver crashes, or black screens during games or GPU-heavy tasks. Fans may surge quickly because GPUs react fast to load.
- NVMe SSD (M.2 drive): Many NVMe drives throttle at higher temperatures. The symptom is subtle: file transfers slow down mid-copy, game load times stretch out, or benchmarks start strong then drop. In small-form-factor cases, an SSD near a GPU can heat soak and perform worse.
- Power supply (PSU): A PSU makes heat and has its own fan (or relies on case airflow, depending on design). Early signs include hot exhaust air, a PSU fan that runs hard, or random shutdowns under load if protection circuits trigger. A burnt smell is rare but urgent, power down and inspect immediately.
- Laptop SoC and nearby components (CPU with integrated GPU, VRMs, memory): Laptops have tight airflow paths and thin heat sinks. Symptoms include hot keyboard or palm rest areas, fans that “hunt” up and down, and performance that drops during long sessions. If the bottom vents are blocked, temperatures can rise fast.
One practical point: dust acts like insulation. It blankets heat sink fins, clogs fan blades, and blocks filters. Even a good cooler fails if air cannot pass through it. Blocked vents matter because they turn the case into a warm box where the same air circulates, raising the baseline temperature for every part inside.
Airflow basics you can explain in one minute: intake, exhaust, and pressure
Air cooling works when you give air a clear route. Think of a PC case like a hallway, air should enter, pass the hot parts, then leave. If air swirls in circles or hits a dead end, components re-breathe warm air and temperatures climb.
Most setups follow two natural patterns:
- Front-to-back: Front fans bring cool air in, rear fans push warm air out. This matches how many cases are built.
- Bottom-to-top: Warm air rises, so bottom intake and top exhaust often helps, especially when a GPU dumps heat upward.
Balancing intake and exhaust matters because it controls pressure and where dust enters.
- Positive pressure means slightly more intake than exhaust. Air tends to leak out through gaps, which reduces dust intake through unfiltered cracks. This is usually easier to keep clean if the intakes have filters.
- Negative pressure means more exhaust than intake. The case pulls air in through any opening, including unfiltered gaps, which can increase dust buildup on heat sinks and fans.
Keep it practical during troubleshooting: airflow problems often come from simple physical issues, not failed parts.
- Clear obstructions: Don’t push a desktop tight against a wall. Leave space behind and above the case so exhaust air can escape.
- Clean and re-seat filters: A clogged front filter can starve all intakes at once, causing higher temps and louder fans.
- Tidy cables near fans: Cable clutter blocks airflow and can create turbulence. You do not need perfect cable art, you need open paths from intake to exhaust.
- Check fan direction: A reversed fan can fight the rest of the airflow and trap heat. Intake should pull cool air in, exhaust should push warm air out.
When airflow is correct, internal temperatures rise more slowly, fans do not have to spike as often, and the system holds steady performance during long workloads. That stability is the real sign of good cooling.
Fans in the real world: types, connectors, and what to check when they fail
Fans are the most visible part of a cooling system, and they are also the part that fails in the most ordinary ways. A fan can stop from dust, a worn bearing, a loose connector, or a control setting that keeps RPM too low. On the A+ exam, you are expected to recognize common fan types, understand basic header wiring, and follow a safe troubleshooting path that fits real repair work.
A useful mental model is simple: fans move air, not heat. The heat still has to move from the chip into a heat sink or radiator. If airflow drops, warm air pools around the hottest parts, and temperatures rise fast.
Fan styles you’ll see on the exam: axial, blower, and built-in device fans
Most PCs use axial fans, the familiar “propeller” style. Axial fans move air in a straight line, from the open side through the frame and out the other side. You see them as case intake and exhaust fans, and on many CPU air coolers where the fan pushes air through heat sink fins. Axial fans work well when there is open space and a clear path, such as front-to-back case airflow.
A blower fan (often called a centrifugal fan) works differently. It pulls air in and throws it out the side through a narrow outlet, like a small air pump. This design is common in laptops and in some GPUs that exhaust hot air out the rear I/O bracket. The key advantage is control. A blower can push air through a tight duct, across a dense fin stack, and out of the device without relying on roomy case airflow.
You will also see built-in device fans, which are often small and fast:
- Laptop fans are usually blower style because the chassis is thin and the airflow path is ducted.
- Small-form-factor desktops and mini PCs may use tiny fans on the CPU or in the power supply.
- Networking gear and servers may use high-RPM fans designed for strong static pressure.
As fans get smaller, they often spin faster to move enough air. High RPM tends to mean more noise and a higher-pitched sound. That matters in troubleshooting, because “loud” can be normal for a small fan under load, while rattling, grinding, or a wobble points to wear.
A quick exam-friendly comparison: blowers help in tight spaces and can exhaust heat directly out of a device, but they can be noisier than larger axial fans moving the same amount of air.
3-pin vs 4-pin (PWM) fan headers, and why the plug matters
Motherboards control fans through headers, and the A+ exam expects you to know the basic difference between 3-pin and 4-pin (PWM) connections. The easiest way to remember this is that both types power the fan, but PWM adds a dedicated control signal.
A typical header uses these signals:
- Ground (GND): the return path for electrical current.
- Power (+12V): supplies power to the fan motor.
- Tachometer (sense): reports fan speed back to the motherboard (RPM feedback).
- PWM control (4th pin): sends a control pulse that tells the fan how fast to spin.
With a 3-pin fan, speed control often happens by changing the voltage on the power pin (DC control). With a 4-pin PWM fan, the board usually keeps a steady 12V supply and controls speed using the PWM signal.