Unplug the fridge before cleaning coils or reaching behind panels. And a boundary worth stating plainly: the sealed system — the refrigerant, the compressor, the closed pipework — is not a home repair. It requires certified handling in most countries, and a "recharge" is not a thing a working fridge ever needs, because the refrigerant is sealed and doesn't get used up. If someone tells you a fridge needs topping up, they're describing a leak, which is a different and larger job. Everything else below is ordinary maintenance. Food safety: if the fridge has been above about 5 °C for more than a few hours, treat perishables with caution.
A fridge doesn't make cold
There is no such thing as cold being produced. A fridge is a heat pump: it collects heat from inside the cabinet and dumps it into your kitchen. That's why the back or bottom of a fridge is warm, and why a fridge running with its door open heats the room rather than cooling it.
The loop is short:
- The compressor pressurises refrigerant.
- The condenser coils — usually a black grille at the back or a coil behind a kick panel underneath — release heat into the room.
- The evaporator coil, hidden behind a panel inside the freezer, absorbs heat from the cabinet.
- A fan blows air across that evaporator and distributes it.
Only the last two steps involve the inside of the appliance, and it's those two that produce nearly all real-world faults.
Why the freezer works and the fridge doesn't
This is the case people search for most, and the answer is structural.
Most modern fridge-freezers are frost-free single-evaporator designs. There is one evaporator coil, and it sits in the freezer compartment. The freezer is cooled directly by it. The fridge compartment is cooled by air ducted across from the freezer by the evaporator fan, usually through a vent with a flap or damper that opens and closes to hold the fridge at temperature.
So "cold freezer, warm fridge" points at exactly three things:
- Frost has built up over the evaporator coil, so air can't pass through it. Covered next — this is the most common by a distance.
- The evaporator fan has failed. The tell: open the freezer and listen. On most machines the fan runs while the door is closed and stops when you open it — some have a door switch, so pressing that switch while listening tells you whether it spins. Silence from the freezer while the compressor hums is a strong signal.
- The vent between compartments is blocked — by food packed against it, or by ice. Fridges have specific vents that must stay clear, and people cover them without knowing.
Frost on the coil — the slow failure
Moisture enters every time a door opens, and it freezes onto the coldest surface, which is the evaporator coil. That's normal and expected. So frost-free fridges include a defrost system: a heater next to the coil, plus a thermostat and a timer or control board, which melts the accumulated frost periodically and drains it away.
When any part of that system fails, the frost never melts. It builds, layer by layer, until it forms a solid block of ice around the coil. Air can no longer pass through, and cooling collapses — gradually, over days or weeks.
The signature is distinctive:
- It got worse slowly rather than stopping suddenly.
- The freezer is still cold, or was until recently.
- There's visible frost build-up — often on the back wall of the freezer, or you can hear the fan hitting ice with a rhythmic ticking or grinding.
- It temporarily improves after the fridge has been switched off for a day, then degrades again over the following week. This is the clearest confirmation there is: switching off manually defrosts the block, and the underlying fault then rebuilds it.
Removing the freezer's back panel reveals the coil. A coil encased in ice rather than lightly frosted confirms it. Manually defrosting — unplug, empty, leave the doors open with towels down for 24 hours or more — restores cooling temporarily and proves the diagnosis, but the defrost heater, thermostat or control board still needs attention or it simply recurs.
One related and cheaper failure in the same family: a blocked defrost drain. Melted frost is meant to run down a small drain hole to a tray near the compressor, where it evaporates. When that hole blocks with debris, the water backs up, refreezes, and you get ice under the salad drawers or water pooling in the bottom of the fridge. Clearing the drain is a genuine home fix.
Dirty condenser coils
If the fridge can't dump heat into the room, it can't remove heat from inside. The condenser coils do that dumping, and they're a dust magnet — particularly the type mounted underneath behind a kick panel.
Symptoms of clogged coils:
- The compressor runs almost constantly and the fridge still isn't cold enough.
- The back or underside is hotter than usual.
- It got worse gradually, and worse still in hot weather.
- Your electricity bill crept up — this is one of the appliance faults that genuinely shows on a bill, since the compressor is running far more than it should.
Homes with pets reach this state much faster; pet hair mats into the coil and the condenser fan blade. Cleaning is unplugging the fridge, removing the kick panel or pulling the unit out, and vacuuming with a brush attachment plus a long coil brush. It's the highest-value maintenance job on the appliance and most people have never done it once.
While you're there: the condenser fan. Many fridges have a second fan near the compressor that blows air across the condenser. If it's seized or clogged, you get exactly the same symptoms as dirty coils.
Door seals and the paper test
A failing door gasket lets warm, humid room air leak in continuously. The fridge fights it by running constantly, frost builds faster than the defrost system can clear it, and cooling still suffers.
Two checks, both free:
- The paper test. Close the door on a sheet of paper and pull. If it slides out easily, the seal isn't gripping at that point. Repeat around all four sides — failures are usually localised to one edge or a corner.
- Look and feel. Gaskets go hard, crack, or tear. They also get sticky with spills, which stops them sitting flat. Warm soapy water often restores a gasket that's merely dirty rather than perished.
Also worth checking: is the fridge level? Most are designed to sit very slightly tilted back so doors self-close. A unit that has been moved onto uneven flooring can end up with doors that don't fully shut, and the symptom looks like a seal fault.
Reading the symptoms
Two questions narrow this down faster than anything else: is the freezer cold? and can you hear the compressor?
To hear the compressor properly, put a hand on the back near the bottom. A running compressor produces a steady low hum and gentle vibration. Fridges also cycle off legitimately, so listen for a few minutes rather than judging on one moment.
The settings that aren't faults
Worth ruling out before dismantling anything, because each of these has caught people out:
- Demo or showroom mode. Many brands include a mode that lights the interior and runs the display but doesn't cool, for shop-floor display. It can be triggered accidentally by a button combination, and it's the most infuriating cause on this list because everything looks normal. The manual explains how to exit it; a display showing something like "d" or "OF" or "demo" is the giveaway.
- Holiday or eco mode, which raises the fridge temperature deliberately.
- The temperature dial was knocked — especially the older type of dial inside the fridge that a shopping bag can turn.
- It was recently very full of warm food, or a door was left ajar. Recovery takes hours, not minutes.
- It was recently moved and switched straight on. After a fridge has been on its side or heavily tilted, manufacturers generally ask you to leave it upright for some hours before powering it up.
- Ambient temperature. A fridge in an unheated garage or an outbuilding can behave strangely — many are rated for a minimum room temperature, and below it the thermostat may stop calling for cooling, leaving the freezer thawing in a cold garage. Counter-intuitive but real, and it's in the manual as a climate class.
- It's jammed against a wall. Fridges need clearance at the back and above to shed heat.
What to check, in order
- Check the setting and look for demo mode. Free, instant, and more common than it should be.
- Is the freezer still cold? If yes, you're looking at airflow — go to step 5.
- Listen for the compressor with a hand on the back. Running, silent, or clicking — this splits the diagnosis.
- Check clearance and ambient temperature, and whether it's in a hot or very cold space.
- Look inside the freezer for frost build-up, and listen for the fan ticking against ice.
- Check the vents inside aren't blocked by food. Free.
- Do the paper test on the door seals, all four sides.
- Unplug and clean the condenser coils and the condenser fan. The single highest-value job here.
- If frost is suspected: unplug and defrost fully for 24 hours or more. If it cools properly afterwards and degrades again over the following week, the defrost system is the fault — and that's the diagnosis to hand to an engineer.
Steps 1 to 8 cost nothing but time. Only step 9 and the sealed system need someone else, and arriving with "it cools after a manual defrost and fails again within a week" turns an open-ended callout into a specific job.
A fridge moves heat out rather than making cold, and on most modern fridge-freezers there's a single cooling coil in the freezer with air ducted across to the fridge. So "freezer cold, fridge warm" is one fault, not two — frost over the coil, a dead evaporator fan, or a blocked vent, all inside the freezer. Frost build-up is the most common, and it identifies itself: it degrades slowly, and it improves for a week after the fridge is switched off and defrosted. If both compartments are warm and the compressor is running, the machine can't dump heat — clean the condenser coils, which almost nobody ever does. Before any of that, check for demo mode and a knocked temperature dial. And no working fridge ever needs a refrigerant top-up; that's a leak, and a different job.