Moisture, condensation or ice in the cold room

Troubleshooting · Applies to: Direct expansion refrigeration system · CO2 booster (transcritical) · Cold rooms with several evaporators

Humidity, condensation and ice in cold rooms: doors and seals, short run times, drainage, wet products and fans after defrost.

Last checked: October 25, 2026 Field mode: large buttons, questions first and the screen kept on.

The moisture nearly always comes in with air, products or defrost water. Danfoss separates cases where the room temperature is normal from cases where it is too high ^[1]^[2]. Look at where the ice or condensation forms: at the door it points to infiltration, at the evaporator to drainage or defrost.

Work on the refrigerant circuit may only be carried out by certified personnel. Isolate the power before working on electrical parts and take particular care with high pressures (CO2) and flammable refrigerants (A2L and A3). Always follow the manufacturer's instructions.

Confirm the fault first

Measure the room temperature and relative humidity and compare with the requirements for the products. Look at where condensation or ice forms: at the door, on the ceiling, at the evaporator or on the floor.

📏 Measurement guide: calculate superheat and subcooling 🔢 Alarm and fault codes

Flowchart

Causes, most likely first

The order is approximate and based on common faults in the field. Always measure before replacing anything.

1
Flowchart A
Warm, humid air leaks in through the door.
Remedy: Repair seals and frame heating, adjust door closers and the door-open alarm, and fit a strip curtain or air curtain.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Check doors, seals and the cold-room envelope
Warm, moist air that leaks into a cold room gives ice on the evaporator, frost on the walls and a higher load. Doors and penetrations are the usual weak points.
1. Test the inside release first. Before you work inside, check from inside that the door opens with the emergency release, even when it is locked from outside. Test the person-trapped alarm button if there is one.
  ✓ Check: The door opens from inside at once, and the alarm sounds where it should.
2. Inspect the gaskets. Look for tears, flattened or hard sections and ice on the gaskets. Close the door on a strip of paper at several points around the frame and pull it out.
  ✓ Check: The paper is held firmly all the way around; places where it slides out easily need a new or adjusted gasket.
3. Check closing and door alarm. Open the door and let it go: check that the closer or self-closing hinges shut and latch it. Leave it open and check that the door-open alarm sounds after its set delay.
  ✓ Check: The door closes and latches by itself, and the alarm works.
4. Check frame and relief port heating. Feel the door frame and, on freezer rooms, the pressure relief port: they should be warm and free of ice and condensation. If not, test the heater circuit (isolate, lock off and prove dead before you touch its terminals; see the guide on heater cables).
  ✓ Check: Frame and relief port are warm and dry, and the relief port flap moves freely.
5. Check strip curtains. Check that the strips overlap, hang down to the floor and are not missing, torn or tied aside.
  ✓ Check: The curtain closes the whole opening.
6. Inspect panel joints and penetrations. Look for frost or ice on the inside and damp on the outside at panel joints and pipe or cable penetrations; an IR camera makes this quicker. Check that penetrations are sealed and that the vapour barrier on the warm side is intact.
  ✓ Check: No frost spots or damp patches, and every penetration is sealed.
Test drain, tray and frame heaters
Heater cables keep drains, drip trays, door frames and pressure relief ports free of ice. A broken heater gives a blocked drain, water on the floor or a frozen door.
1. Isolate, lock off and prove dead. Switch off and lock the isolator for the heater circuit, attach a tag and prove dead with a two-pole voltage tester (checked on a known live source before and after) at the heater terminals.
  ✓ Check: The tester shows no voltage between the conductors and between each conductor and earth.
2. Check fuse, thermostat and control output. Check the fuse or circuit breaker for the heater and the thermostat or controller relay that switches it. A drain heater is often switched only during defrost; a frame heater is often on all the time. Read the wiring diagram.
  ✓ Check: The fuse is intact and you know when the heater should be on.
3. Measure the resistance. Disconnect the heater leads and measure resistance across the element. Calculate the expected value from the nameplate: R = V² / P (for example 230 V, 100 W gives about 530 Ω). Self-regulating cables cannot be judged this way; check them by current instead.
  ✓ Check: The reading is close to the calculated value; OL (open) means a broken element, near 0 Ω means a short.
4. Measure insulation resistance to earth. Use an insulation tester at 500 V DC between the joined heater conductors and the earth conductor or metal braid, with the heater disconnected from any electronics.
  ✓ Check: At least 1 MΩ (IEC 60364-6 minimum for 230/400 V circuits); a low or falling value means moisture in the cable or end seal.
5. Measure voltage and current in operation. Reconnect, refit the covers and switch on. Make the controller call for the heater (or start a defrost), then measure voltage at the heater and current with a clamp meter. Expected current is about P / V.
  ✓ Check: The heater gets full voltage and draws roughly the nameplate current.
6. Check the heater position. Check that the drain heater runs the full length of the drain inside the cold space and through the wall, that the tray heater lies against the tray, and that the frame heater warms the whole door frame.
  ✓ Check: After the next defrost the drain runs freely and the frame is warm and free of ice.
2
Flowchart C
The defrost water does not drain away.
Remedy: Clean tray and drain, check fall and trap and, in freezers, the heater cable in the drain line.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Clear the condensate drain
A blocked or frozen drain lets melt water overflow into the room and freeze on the floor or the coil. Clear it, then fix the cause: fall, trap or a dead heater cable.
1. Isolate and protect yourself. Isolate, lock off and prove dead the evaporator before working at the tray. Wet cold-room floors are slippery: wear shoes with grip and tell someone you are inside.
  ✓ Check: The meter shows 0 V on the evaporator terminals.
2. Thaw and clean the tray and drain. Thaw ice in the tray and drain with warm water. Clean out slime and debris with a flexible drain brush.
  ✓ Check: Warm water poured into the tray runs straight out without backing up.
3. Measure the heater cable resistance. With the power still off, disconnect the drain heater cable and measure its resistance. Calculate the expected value from the rating (R = U² / P) or take it from the data sheet. Check the fuse and the thermostat, if any.
  ✓ Check: The resistance is close to the expected value; OL (open) means a broken cable.
4. Check the heater in operation. Reconnect, refit covers and switch on. Measure the current with a clamp meter and feel or measure that the drain warms along its full length inside the cold room.
  ✓ Check: The current matches the rating and the drain is warm all the way out of the room.
5. Check fall and trap. Check with a spirit level that the drain has a continuous fall with no sags. In freezer rooms the trap should be outside the cold room, in the warm area, so it cannot freeze.
  ✓ Check: The drain falls all the way, the trap holds water and is placed where it cannot freeze.
6. Run a defrost and check. Start a defrost and watch the melt water.
  ✓ Check: All melt water leaves the room and nothing refreezes in the tray or drain.
Test drain, tray and frame heaters
Heater cables keep drains, drip trays, door frames and pressure relief ports free of ice. A broken heater gives a blocked drain, water on the floor or a frozen door.
1. Isolate, lock off and prove dead. Switch off and lock the isolator for the heater circuit, attach a tag and prove dead with a two-pole voltage tester (checked on a known live source before and after) at the heater terminals.
  ✓ Check: The tester shows no voltage between the conductors and between each conductor and earth.
2. Check fuse, thermostat and control output. Check the fuse or circuit breaker for the heater and the thermostat or controller relay that switches it. A drain heater is often switched only during defrost; a frame heater is often on all the time. Read the wiring diagram.
  ✓ Check: The fuse is intact and you know when the heater should be on.
3. Measure the resistance. Disconnect the heater leads and measure resistance across the element. Calculate the expected value from the nameplate: R = V² / P (for example 230 V, 100 W gives about 530 Ω). Self-regulating cables cannot be judged this way; check them by current instead.
  ✓ Check: The reading is close to the calculated value; OL (open) means a broken element, near 0 Ω means a short.
4. Measure insulation resistance to earth. Use an insulation tester at 500 V DC between the joined heater conductors and the earth conductor or metal braid, with the heater disconnected from any electronics.
  ✓ Check: At least 1 MΩ (IEC 60364-6 minimum for 230/400 V circuits); a low or falling value means moisture in the cable or end seal.
5. Measure voltage and current in operation. Reconnect, refit the covers and switch on. Make the controller call for the heater (or start a defrost), then measure voltage at the heater and current with a clamp meter. Expected current is about P / V.
  ✓ Check: The heater gets full voltage and draws roughly the nameplate current.
6. Check the heater position. Check that the drain heater runs the full length of the drain inside the cold space and through the wall, that the tray heater lies against the tray, and that the frame heater warms the whole door frame.
  ✓ Check: After the next defrost the drain runs freely and the frame is warm and free of ice.
3
The door frame heater or the drain heater cable has failed.
Remedy: Measure resistance and voltage, and check the fuse.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Test drain, tray and frame heaters
Heater cables keep drains, drip trays, door frames and pressure relief ports free of ice. A broken heater gives a blocked drain, water on the floor or a frozen door.
1. Isolate, lock off and prove dead. Switch off and lock the isolator for the heater circuit, attach a tag and prove dead with a two-pole voltage tester (checked on a known live source before and after) at the heater terminals.
  ✓ Check: The tester shows no voltage between the conductors and between each conductor and earth.
2. Check fuse, thermostat and control output. Check the fuse or circuit breaker for the heater and the thermostat or controller relay that switches it. A drain heater is often switched only during defrost; a frame heater is often on all the time. Read the wiring diagram.
  ✓ Check: The fuse is intact and you know when the heater should be on.
3. Measure the resistance. Disconnect the heater leads and measure resistance across the element. Calculate the expected value from the nameplate: R = V² / P (for example 230 V, 100 W gives about 530 Ω). Self-regulating cables cannot be judged this way; check them by current instead.
  ✓ Check: The reading is close to the calculated value; OL (open) means a broken element, near 0 Ω means a short.
4. Measure insulation resistance to earth. Use an insulation tester at 500 V DC between the joined heater conductors and the earth conductor or metal braid, with the heater disconnected from any electronics.
  ✓ Check: At least 1 MΩ (IEC 60364-6 minimum for 230/400 V circuits); a low or falling value means moisture in the cable or end seal.
5. Measure voltage and current in operation. Reconnect, refit the covers and switch on. Make the controller call for the heater (or start a defrost), then measure voltage at the heater and current with a clamp meter. Expected current is about P / V.
  ✓ Check: The heater gets full voltage and draws roughly the nameplate current.
6. Check the heater position. Check that the drain heater runs the full length of the drain inside the cold space and through the wall, that the tray heater lies against the tray, and that the frame heater warms the whole door frame.
  ✓ Check: After the next defrost the drain runs freely and the frame is warm and free of ice.
4
Humid air leaks in through unsealed pipe and cable penetrations, panel joints, or a pressure relief port that is frozen or broken (freezer rooms).
Remedy: Look for ice or condensation in spots on the ceiling and walls. Seal the penetrations and joints on the warm side, and check the heater and flap of the pressure relief port.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Check doors, seals and the cold-room envelope
Warm, moist air that leaks into a cold room gives ice on the evaporator, frost on the walls and a higher load. Doors and penetrations are the usual weak points.
1. Test the inside release first. Before you work inside, check from inside that the door opens with the emergency release, even when it is locked from outside. Test the person-trapped alarm button if there is one.
  ✓ Check: The door opens from inside at once, and the alarm sounds where it should.
2. Inspect the gaskets. Look for tears, flattened or hard sections and ice on the gaskets. Close the door on a strip of paper at several points around the frame and pull it out.
  ✓ Check: The paper is held firmly all the way around; places where it slides out easily need a new or adjusted gasket.
3. Check closing and door alarm. Open the door and let it go: check that the closer or self-closing hinges shut and latch it. Leave it open and check that the door-open alarm sounds after its set delay.
  ✓ Check: The door closes and latches by itself, and the alarm works.
4. Check frame and relief port heating. Feel the door frame and, on freezer rooms, the pressure relief port: they should be warm and free of ice and condensation. If not, test the heater circuit (isolate, lock off and prove dead before you touch its terminals; see the guide on heater cables).
  ✓ Check: Frame and relief port are warm and dry, and the relief port flap moves freely.
5. Check strip curtains. Check that the strips overlap, hang down to the floor and are not missing, torn or tied aside.
  ✓ Check: The curtain closes the whole opening.
6. Inspect panel joints and penetrations. Look for frost or ice on the inside and damp on the outside at panel joints and pipe or cable penetrations; an IR camera makes this quicker. Check that penetrations are sealed and that the vapour barrier on the warm side is intact.
  ✓ Check: No frost spots or damp patches, and every penetration is sealed.
5
Flowchart E
The fans start too early after defrost and blow meltwater and moisture into the room.
Remedy: Set the drip time and fan delay after defrost according to the evaporator manufacturer.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Check the defrost system
Incomplete defrost leaves ice on the evaporator, which reduces capacity and can block the airflow completely. Check heaters or hot gas, termination, interval, drip time and fan delay.
1. Check the defrost settings. Read defrost type, interval, maximum time, termination temperature, drip time and fan delay in the controller and compare with the manufacturer's recommendations. Check the controller clock if defrosts are scheduled.
  ✓ Check: The settings match the application and the clock is right.
2. Measure the heater resistance. Isolate, lock off and prove dead, then disconnect the heaters and measure each one. The expected resistance is R = U² ÷ P from the heater's voltage and power. Also measure insulation to earth with an insulation tester.
  ✓ Check: Each heater is close to the calculated value and has no earth fault; OL means a broken heater.
3. Measure the current during defrost. Restore power, start a manual defrost and measure the current in each heater supply with a clamp meter. Watch out for hot surfaces.
  ✓ Check: The current is about P ÷ U for each heater, or matches the nameplate defrost current.
4. Check hot gas defrost. On hot gas systems, check that the hot gas valve opens (warm pipe after the valve) and that the liquid or suction valves close as intended. Never exceed the system PS.
  ✓ Check: Hot gas reaches the evaporator and the coil warms evenly.
5. Check termination. Check that the termination sensor sits on the coldest part of the coil, usually where ice remains longest, and that the defrost ends on temperature rather than on maximum time.
  ✓ Check: The defrost ends on temperature and the coil is completely free of ice.
6. Check drip time and fan delay. After the defrost, watch the drip time and the evaporator fans when refrigeration restarts. Check that the drain and the drip tray heater work.
  ✓ Check: Fans stay off until the coil has reached the fan-delay setpoint, and water drains without refreezing in the tray.
6
Flowchart B
Run times too short: the evaporator removes too little moisture.
Remedy: Troubleshoot short cycling and check that the system is not heavily oversized.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Compare cooling load with system capacity
If a room never reaches its temperature, or the plant cycles all the time, compare the actual load with what the plant can deliver at the conditions you measure.
1. Record conditions. Measure room temperature and humidity, the surrounding temperature outside the room, and the temperature of products as they come in. Note evaporating and condensing temperatures.
  ✓ Check: You have a set of values measured at the same time.
2. Collect room and use data. Note room size, insulation type and thickness, product quantity per day and its entry temperature, door openings, people, lighting, fans and defrost.
  ✓ Check: Every load source has a value or a reasoned estimate.
3. Calculate the load. Calculate the load per 24 hours with the Kylbehov app or a recognised method (for example the cooling load chapter in the ASHRAE Refrigeration Handbook), and divide by the planned run time per day, which leaves time for defrost.
  ✓ Check: You have the required capacity in kW at the room's design conditions.
4. Find the actual capacity. Read evaporator capacity at the actual temperature difference between room air and evaporation, and compressor capacity at the measured evaporating and condensing temperatures, from the manufacturers' data. Note that rated capacities apply to standard conditions.
  ✓ Check: You have evaporator and compressor capacity at the real conditions; the lower one limits the system.
5. Compare with run time. Read compressor run time and starts per hour from the controller log. Compare required and actual capacity.
  ✓ Check: Capacity below the load, or near-continuous running, shows undersizing or excess load; very short cycles and many starts show oversizing.
6. Decide on measures. Reduce the load first (doors, curtains, product temperature, envelope), then consider more capacity or a different control strategy. Write down the comparison.
  ✓ Check: A written comparison of load and capacity with the chosen measure.
Continue with: Compressor short cycling →
7
Flowchart D
Moisture load from the products.
Remedy: Let warm products cool, cover them and do not place them directly in front of the evaporator.

Checks from the manufacturers’ manuals (8)

Values and checks the manufacturers give for their own products; they apply to the product named.

Heatcraft unit coolers: Ice on the ceiling around the evaporator or on the fan guards: the defrost lasts too long or runs too often, so warm moist air escapes from the coil, or the fan delay after defrost does not work.^[3]
AHT Kinley XL with Nidec controller: Plug-in cabinets with door or frame heating: on some controllers switching the cooling off (for cleaning) also switches the door heating off, and it stays off after cooling is switched back on until someone turns it on by hand, so the glass and frame fog up or drip.^[4]
Krack MK/MV and MK-A2L/MV-A2L unit coolers: Too many defrosts per day, or a defrost that ends too late because the termination thermostat or timer is faulty, makes the coil steam; the vapour freezes on the ceiling. Reduce the number of defrosts and check the termination.^[5]
Krack MS-A2L unit coolers: Steam from the unit cooler during defrost, and ice on the ceiling above it, mean the defrost runs too long (termination thermostat or timer) or there are too many defrosts.^[6]
HTPG EcoNet unit coolers: The defrost runs too long, so the coil steams and the vapour condenses or freezes on the ceiling and around the unit cooler. HTPG says unit coolers should not defrost longer than about 30-35 minutes; lower the termination temperature and the maximum defrost time.^[7]
Hussmann FS-OB display cases: Water under a display case: a blocked drain screen or P-trap, a case that is not level, a leaking drain pipe, an unsealed opening in the tub or a missing seal between cases in a line-up.^[8]
Krack KR-A2L; Wessamat CubeLine; ITV NG: Unit cooler or ice machine that overflows: a dirty drip tray, a blocked drain line or bin drain, or a drain hose that is kinked.^[9]
Hussmann VRM glass door merchandisers: Glass-door cabinets: doors that do not close on their own (hinge spring torque set too low or a door sagging) or gaskets with gaps after transport let warm humid air in; the doors should swing shut by themselves and the gasket should seal all round.^[10]

📝 Fill in a service report

Moisture, condensation or ice in the cold room

Confirm the fault first

Troubleshoot step by step

Flowchart

Causes, most likely first

Check doors, seals and the cold-room envelope

Test drain, tray and frame heaters

Clear the condensate drain

Test drain, tray and frame heaters

Test drain, tray and frame heaters

Check doors, seals and the cold-room envelope

Check the defrost system

Compare cooling load with system capacity

Checks from the manufacturers’ manuals (8)

Service report

Sources