Ice cream machine does not freeze (product too soft)

Causes, most likely first

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

1. 1
   Flowchart B

   More is dispensed than the machine can freeze, or it is used too soon after start-up or storage mode.

   Remedy: Dispense within the rated output and wait about 10 minutes after start-up before serving.

2. 2
   Flowchart C

   Wrong mix (too much sugar, diluted, warm or old) or a consistency setting that has been lowered.

   Remedy: Use the right mix according to the recipe, pre-cool it and reset the consistency to the value for the product.

   🛠 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.

   Set mix, consistency and draw rate

   A soft-serve or ice-cream machine gives the right product only when the mix, the consistency setting and the draw rate fit together. Work hygienically throughout: everything that touches the product must be clean and sanitised.

   1. Clean and sanitise first. Wash your hands and sanitise all parts that touch the mix (hopper, cylinder, beater, door, draw valve) with a food-safe sanitiser as the machine manual describes. Use only food-safe lubricant on O-rings.

      ✓ Check: All product-contact parts are clean, sanitised and correctly assembled.

   2. Check the mix and its brix. Put a drop of the mix on a clean refractometer and read the brix. Compare with the value from the mix supplier or recipe. A brix that is too low or too high changes how hard the product freezes.

      ✓ Check: The brix agrees with the supplier's or recipe value.

   3. Check the hopper temperature. Measure the mix temperature in the hopper with a clean probe thermometer and compare it with the manual and local food safety rules (usually about 4 °C or colder).

      ✓ Check: The mix in the hopper holds the temperature in the manual.

   4. Set the consistency. Set the consistency (hardness) in the controller as the manual describes, in small steps. Most machines measure the beater motor current or torque. Let the machine run a full freezing cycle after each change.

      ✓ Check: The product holds its shape when drawn and the machine stops freezing at the set consistency.

   5. Weigh the draw rate. Tare a cup on the scales, draw product for a timed period (for example 10 seconds) and weigh it. Divide by the time and compare with the draw rate for the model in the manual.

      ✓ Check: The draw rate in g/s agrees with the model value.

   6. Adjust and record. If the draw rate or texture is wrong, check the air/mix feed tube or pump setting and the consistency again, then repeat the weighing. Record brix, temperature, consistency setting and draw rate.

      ✓ Check: The final settings are recorded and the product meets the specification.

3. 3
   Flowchart A

   The condenser cannot get rid of the heat: dirty air-cooled condenser, a stopped condenser fan, too little space or a hot room, or too little or too warm cooling water.

   Remedy: Clean the condenser with a brush or compressed air, check that the condenser fan runs, keep at least 50 cm free behind the machine and check the cooling water valve, strainer and water temperature.

   🛠 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.

   Clean a condenser or gas cooler

   A dirty condenser or gas cooler raises the condensing pressure, the power consumption and the risk of high pressure trips. Clean it, straighten the fins and check that air can flow freely.

   1. Measure before you clean. With the system running, note the condensing pressure (or gas cooler outlet temperature on CO2) and the air-on temperature, so that you can see the effect afterwards.

      ✓ Check: Pressure and air temperature are recorded.

   2. Isolate and lock off. Isolate the condensing unit and fans, lock and tag the isolator and prove dead at the fan motor terminals. Fans can otherwise start automatically. On roofs, use fall protection.

      ✓ Check: 0 V at the fan terminals and the fans have stopped.

   3. Remove loose dirt. Brush off leaves and fluff from the air-entering side with a soft brush along the fins. Blow or rinse from the air-leaving side, against the normal airflow, so dirt is pushed out rather than in.

      ✓ Check: The surface of the coil is free of loose dirt.

   4. Clean with coil cleaner and water. Protect fan motors and electrical parts from water. Apply a coil cleaner suitable for the fin material, follow its safety data sheet (gloves and goggles) and rinse with low-pressure water against the normal airflow. Never use a high-pressure washer, which flattens the fins.

      ✓ Check: The rinse water runs clear and the fins are undamaged.

   5. Straighten fins and check clearances. Straighten bent fins with a fin comb of the right pitch. Check that nothing blocks the air inlet or outlet and that warm air cannot recirculate to the inlet (walls, snow, other units).

      ✓ Check: Fins are straight and the free distances around the unit match the installation instructions.

   6. Restart and compare. Remove your lock, restore power and let the system stabilise. Compare the condensing pressure and the air-on temperature with the values before cleaning.

      ✓ Check: The condensing temperature is lower at a similar air temperature.

   Check a condenser or evaporator fan motor

   A fan that stops, runs slowly or turns the wrong way gives high pressure on the condenser side, or low pressure and ice on the evaporator side. Check the supply, the control signal, the motor and the fan itself.

   1. Look and listen with the unit running. Watch the fan from a safe distance: does it run, at what speed, and in the right direction (air through the coil the way the arrow on the housing or the manual shows)? Listen for bearing noise and look for ice, dirt or a damaged blade.

      ✓ Check: You know whether the fan is stopped, slow, noisy or turning the wrong way.

   2. Check the supply and the control signal. Measure the voltage at the motor terminals or the EC fan connector with the fan called for. For an EC fan also measure the control signal (0–10 V or PWM) and read any status lamp or fault code on the fan electronics. Check fan delay settings and thermostats in the controller: a fan that is held off on purpose is not faulty.

      ✓ Check: Supply voltage is within the rated range on the nameplate, and the control signal asks for the fan to run; otherwise the fault is upstream (contactor, fuse, controller output, wiring).

   3. Isolate, lock off and make sure the fan cannot start. Switch off and lock the isolator, prove the circuit dead with a tested two-pole tester, and wait for the fan to stop completely. Remember that an EC fan can restart on its own when the signal returns, and that a fan wind-milling in a draught can generate voltage.

      ✓ Check: 0 V on the motor terminals and the blades are blocked or stationary.

   4. Turn the fan by hand and check it mechanically. Turn the impeller by hand: it should spin freely and evenly, without scraping, axial play or a rough bearing. Check that the blades are tight on the shaft and not cracked, and that the guard and the coil are free of ice, dirt and loose objects.

      ✓ Check: The fan turns freely and quietly and the blades are undamaged; a stiff or rough motor must be replaced.

   5. Measure the motor (AC motors). With the motor disconnected, measure the winding resistance between the terminals and compare the windings with each other and with the data sheet; test the run capacitor (see the capacitor guide). Measure the insulation resistance to earth with an insulation tester – never with the fan electronics or an EC motor connected. Check that the motor's internal thermal protection is closed when the motor is cold.

      ✓ Check: Windings are equal where they should be and match the data sheet, insulation resistance is well above the limit your electrical rules require, and the thermal protection is closed when cold.

   6. Restore, run and measure the current. Reconnect from your photo, fit guards and covers, remove the lock and start. Measure the running current on each phase and compare it with the nameplate, and check the direction and the air flow.

      ✓ Check: The fan runs smoothly in the right direction, the current is at or below the nameplate value and the pressures settle (head pressure falls on a condenser, suction pressure rises and ice clears on an evaporator).

   Check head pressure control

   Too low condensing pressure in winter starves the expansion valve; too high in summer costs energy and trips the HP switch. Check fan control, head pressure valves and water regulating valves against the setpoint.

   1. Read the condensing pressure and setpoint. Connect a calibrated gauge to the discharge or liquid line port and note the condensing pressure setpoint and fan stages in the controller or speed controller. Never exceed the system PS.

      ✓ Check: You know the actual condensing pressure and the setpoint.

   2. Check fan staging and speed control. Watch the fans as the pressure rises and falls: stages cut in and out, or the speed changes, around the setpoint. Measure the speed controller output if a fan does not respond.

      ✓ Check: Fans start, stop or change speed at the set pressures.

   3. Check the fans with power off. If a fan does not run, isolate and lock off, check the fan motor and blades and that the coil is clean before blaming the control. Fans can start automatically.

      ✓ Check: Fans turn freely and the condenser is clean.

   4. Check head pressure valves in cold weather. On systems with head pressure valves (e.g. Sporlan ORI/ORD or Danfoss KVR/NRD), check during low ambient that the bypass to the receiver gets warm when the valve regulates, and that there is enough refrigerant for the flooded condenser (winter charge, sight glass full).

      ✓ Check: The condensing pressure is held at the valve setting and the sight glass stays full in cold weather.

   5. Check the water regulating valve. On water-cooled condensers, check that the water regulating valve opens more as the condensing pressure rises and closes at standstill. Compare water in and out temperatures.

      ✓ Check: The valve modulates and the condensing pressure is steady; no water flows at standstill.

   6. CO2 gas coolers. On transcritical CO2 (R744) the high pressure is set by the high pressure valve and the gas cooler fans together; check it as described in the CO2 high pressure valve guide.

      ✓ Check: Gas cooler outlet temperature and high pressure follow the controller setpoints.

   Continue with: System trips on high pressure →

4. 4
   Flowchart D

   Too little mix reaches the cylinder: low level, the pump draws air or does not build pressure, or worn O-rings and valves give wrong overrun.

   Remedy: Top up the mix, check the pump, O-rings and air valve, refit the parts correctly and bleed the cylinder.

   🛠 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.

   Prime the ice-cream cylinder and mix pump

   Air in the cylinder or a pump that does not feed gives a runny or frozen product and can damage the beater. Assemble, lubricate and prime by the manual.

   1. Clean and sanitise. Wash your hands and sanitise the hopper, pump parts, feed tube and cylinder with an approved sanitiser. Keep the machine stopped while your hands are in the hopper or cylinder.

      ✓ Check: All product-contact parts are clean and sanitised.

   2. Check and lubricate the O-rings. Check the O-rings on the pump, feed tube and air valve for cracks and replace damaged ones. Lubricate them with food-grade lubricant and assemble the pump.

      ✓ Check: The pump parts turn freely by hand and every O-ring is whole and lubricated.

   3. Fill the hopper with chilled mix. Pour chilled mix into the hopper up to the fill line. The mix must be kept cold, normally 4 °C or below, or as the mix supplier and local food rules require.

      ✓ Check: The mix is above the minimum line and at the required temperature.

   4. Prime the cylinder. Open the air valve or the priming plug and let the mix flow into the cylinder until air stops coming out.

      ✓ Check: Mix runs out without air bubbles; close the valve or plug.

   5. Start freezing and check the feed. Start the freeze mode and check that the pump keeps the cylinder fed and the feed tube is seated correctly.

      ✓ Check: The product reaches its normal consistency and the cylinder does not run empty.

   6. Check for leaks. Check the door, the rear seal and the pump for drips.

      ✓ Check: No mix leaks at the door, rear seal or pump.

5. 5
   Flowchart E

   Worn scrapers or bushing, or a slipping or broken belt, so ice insulates the cylinder wall or the beater turns too slowly.

   Remedy: Replace worn scrapers and bushing, tension or replace the belt and check the pulleys.

   🛠 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.

   Service scrapers, beater and drive

   Worn scraper blades and bushings give poor freezing and a soft product, and a slipping belt or loose coupling stops the beater. Service them at the interval in the manual.

   1. Empty, clean and isolate. Drain the mix and clean the cylinder as the manual describes. Isolate, lock off and prove dead before opening the drive or touching the beater: the drive can start automatically.

      ✓ Check: The meter shows 0 V on the motor terminals and the drive cannot start.

   2. Remove and inspect the beater. Wear cut-resistant gloves. Remove the front door and the beater. Check the scraper blades for nicks and wear, and the bushings and shaft seal for wear.

      ✓ Check: Worn or nicked blades and worn bushings are found and noted.

   3. Replace worn parts. Fit new scraper blades, bushings and seals with the manufacturer's spare parts. Replace the blades as a set.

      ✓ Check: The blades sit firmly on the beater and the bushings fit without play.

   4. Check the belt and coupling. Open the drive cover. Check the belt for cracks and wear and set the tension with a belt tension gauge to the manufacturer's value. Check the coupling and the gearbox for play and leaks.

      ✓ Check: The belt tension is within the manufacturer's value and the coupling has no play.

   5. Check the motor wiring. With the power still off, check the motor terminals for tight, undamaged connections and measure the winding resistance.

      ✓ Check: The terminals are tight and the winding readings agree with the motor data; no winding is open.

   6. Sanitise and reassemble. Wash and sanitise all parts in contact with the product, lubricate O-rings and seals with food-grade lubricant and reassemble the beater and door.

      ✓ Check: The beater turns freely by hand and the door seals without leaks.

   7. Test run. Remove your lock, switch on and run the beater (wash mode) with water or sanitiser before filling mix.

      ✓ Check: The beater runs quietly, the belt does not slip and nothing leaks at the door or rear seal.

6. 6
   Flowchart F

   Too little refrigerant or a restriction: low suction pressure, high superheat and long running times.

   Remedy: Troubleshoot the low pressure: leak test and repair before charging to the data plate.

   🛠 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.

   Leak test a refrigeration system

   Find leaks systematically, confirm the repair and record the work. Work that opens the refrigerant circuit requires F-gas certification (Regulation (EU) 2024/573 or national equivalent, EPA 608 in the USA).

   1. Prepare the system and the detector. The system must be under pressure (running, or at standstill with warm ambient). Stop fans in the area to get calm air and ventilate low or enclosed spaces. With A2L/A3 refrigerants use no ignition sources and only detectors rated for them; with CO2 (R744) remember the very high pressure. Check the electronic detector (EN 14624) against its reference leak or as the manufacturer describes.

      ✓ Check: The detector reacts to the reference leak, and the air around the system is calm.

   2. Search with the electronic detector. Move the probe slowly, a few centimetres per second, close to every brazed joint, flare, valve stem, Schrader core, gauge and coil bend. Refrigerants are heavier than air, so hold the probe at and below each joint. Follow the circuit in a fixed order so that nothing is missed.

      ✓ Check: Every joint along the circuit has been passed, and each alarm has been repeated at the same spot.

   3. Confirm with bubble solution. Spray bubble leak solution on each suspected point and watch it for at least a minute; small leaks form bubbles or foam slowly.

      ✓ Check: Bubbles or foam pinpoint the leak, or the point is confirmed tight.

   4. Use UV dye only where it is approved. If the system already contains a UV dye approved by the compressor manufacturer, light the joints with a UV lamp and wear UV glasses.

      ✓ Check: A fluorescent trace marks the leak, or no trace is visible.

   5. Repair correctly. Recover the refrigerant (or isolate the section), repair with nitrogen flowing when brazing, pressure test with nitrogen, evacuate and charge by weight. Never top up refrigerant 'to test' without finding and repairing the leak.

      ✓ Check: The repaired joint holds the nitrogen test pressure and the system is charged with the specified amount.

   6. Record and re-check. Write the leak location, cause, repair, refrigerant amount and your certificate number in the equipment logbook. Check the repair again within one month, as the F-gas regulation requires.

      ✓ Check: The logbook entry is complete and a follow-up check is booked.

   Charge refrigerant by weight

   The only reliable way to get the correct charge is to weigh it in. The system must be leak tight, pressure tested and evacuated first, and the work must be done by F-gas certified personnel.

   1. Check that the system is ready. Check that leaks are repaired, the nitrogen pressure test is passed and the system is evacuated with a passed decay test (see those guides). Find the charge on the nameplate plus any addition for pipe length given by the manufacturer.

      ✓ Check: Records of the tests exist and you know the total charge in kg.

   2. Set up cylinder and scale. Check the refrigerant on the cylinder label (not by colour). Place the cylinder on a calibrated scale on a level surface, connect evacuated or low-loss hoses and zero the scale. On A2L/A3 systems: no ignition sources, ventilation and a gas detector.

      ✓ Check: The scale reads zero and the hoses are free of air.

   3. CO2 only: break the vacuum with vapour. On a CO2 system, charge vapour first until the pressure is well above the triple point (5.2 bar absolute) before any liquid goes in. Liquid into a deep vacuum turns to dry ice.

      ✓ Check: The system pressure is above 5.2 bar absolute before liquid charging starts.

   4. Charge liquid into the high side. With the system off, charge liquid into the receiver or liquid line. Always charge blends (400 series) as liquid. Watch the scale and close when the target is reached.

      ✓ Check: The scale shows the weight that has left the cylinder.

   5. Add the rest carefully. If not all of the charge goes in, start the system and add the remainder slowly into the suction side through a throttled valve, so that liquid does not reach the compressor. Never exceed the nameplate charge.

      ✓ Check: The total on the scale equals the target charge.

   6. Check operation. Run until stable and measure superheat and subcooling.

      ✓ Check: Both are within the manufacturer's targets.

   7. Disconnect and record. Close the cylinder, remove the hoses with minimal loss, refit the caps and leak test the ports. Record type and quantity charged in the logbook.

      ✓ Check: The caps are on, no leak is found and the logbook shows the charged quantity.

   Continue with: System trips on low pressure →

7. 7

   Electrical fault: a worn compressor contactor, a tripped overload, low voltage or wrong phase sequence after electrical work (the beater turns the wrong way).

   Remedy: Measure voltage and current, check the contactor and overloads and correct the phase sequence.

   🛠 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.

   Measure voltage and current under load

   Low voltage, phase imbalance or high current make motors overheat and trip. Measure at standstill, during start and in operation and compare with the nameplate. Live measurements in an open panel are for qualified personnel only.

   1. Prepare for live measurement. Use a CAT III/IV multimeter with insulated probes and a true-RMS clamp meter with inrush function. Wear safety glasses, no loose clothing, and keep hands clear of fans and belts that can start automatically.

      ✓ Check: Meter and leads are CAT III or CAT IV rated and the meter works on a known source.

   2. Measure the supply at standstill. Measure L1–L2, L2–L3 and L3–L1 (and phase to neutral where used) at the incoming terminals with the compressor stopped.

      ✓ Check: All voltages are within the range on the nameplate or data sheet (many compressors allow ±10 % of rated voltage).

   3. Measure voltage during start and in operation. Measure the same phases at the compressor contactor while the compressor starts and again after a few minutes of running. A large drop during start points to a weak supply, undersized cables or a loose connection.

      ✓ Check: The voltage stays within the permitted range also during start and in operation.

   4. Calculate the voltage imbalance. Imbalance (%) = largest deviation from the average of the three phase-to-phase voltages ÷ average × 100.

      ✓ Check: The imbalance is within the compressor manufacturer's limit (often about 2 %).

   5. Measure the current on each phase. Clamp each phase conductor separately: the inrush current at start and the running current after the system has stabilised.

      ✓ Check: The running current does not exceed the rated load amps (RLA) on the nameplate and is about equal on all three phases.

   6. Record and act. Write voltages, imbalance and currents in the service report. High voltage drop: tighten and check connections under isolation. Imbalance or high current: trace the supply or the motor before restarting repeatedly.

      ✓ Check: Readings are documented and any fault is traced to supply, connection or motor.

   Test a contactor

   Worn, welded or loosely connected contactor contacts cause single-phasing, overheating and motor damage. Check the contacts, the coil and the voltage drop, and replace a worn contactor. Electrical work is for qualified personnel only.

   1. Isolate and lock off. Switch off and lock the isolator, attach a tag and prove dead with a two-pole voltage tester on all line and load terminals, also the coil supply, which can come from a separate control circuit.

      ✓ Check: 0 V on all poles, the coil terminals and to earth.

   2. Inspect the contacts and the mechanism. Remove the arc cover if the design allows. Look for heavily pitted, burnt or welded contacts, and discoloured terminals or melted plastic. Press the armature by hand (power off) and check that it moves freely and springs back.

      ✓ Check: Contacts are without heavy pitting or welds, and the armature moves freely.

   3. Check the coil. Disconnect one coil lead and measure the coil resistance. Compare with the manufacturer's data or a new contactor of the same type.

      ✓ Check: The coil is neither open (OL) nor near 0 Ω.

   4. Check the coil voltage and pull-in. Reconnect, remove your lock, restore power and use the CAT III/IV meter to measure the voltage across the coil when the controller calls for operation.

      ✓ Check: The coil voltage matches the rating printed on the coil, and the contactor pulls in firmly without humming or chattering.

   5. Measure the voltage drop across each pole. With the motor running, measure from line to load terminal across each closed pole.

      ✓ Check: The drop is close to 0 V and about equal on all poles; a pole with clearly higher drop has worn contacts.

   6. Tighten or replace. Isolate and lock off again. Tighten all terminals to the manufacturer's torque. Replace a worn contactor with one of the same coil voltage and at least the same motor rating (AC-3), then restart and measure the current on each phase.

      ✓ Check: Terminals are tight, and the motor current is about equal on all phases after restart.

   Check and correct phase sequence

   Scroll and screw compressors and many fans must run in the right direction. A scroll compressor running backwards is noisy, does not pump and is damaged quickly.

   1. Measure the phase sequence. With the unit stopped, connect a phase rotation meter to L1, L2 and L3 at the unit's supply terminals (live measurement: CAT III/IV, insulated probes). If the unit has a phase monitoring relay, read its indicator too.

      ✓ Check: The meter shows right-hand (L1-L2-L3) rotation, or you know that it is reversed.

   2. Decide where to swap. If the whole unit is reversed, swap at the unit's supply terminals after the isolator. If only one motor runs backwards, swap at that motor. For a motor on an inverter, the input sequence does not matter; change direction with a parameter or at the drive output.

      ✓ Check: You know which two conductors to swap and where.

   3. Isolate, lock off and prove dead. Switch off and lock the isolator, attach a tag and prove dead with a two-pole voltage tester on all phases and to earth.

      ✓ Check: The tester shows no voltage on any phase.

   4. Swap two phases. Swap two phase conductors (for example L1 and L2). Never move the earth or neutral conductor. Tighten the terminals to the specified torque.

      ✓ Check: Two phases are swapped and the terminals are tight.

   5. Check the sequence again. Remove your lock, switch on and measure the phase sequence again; check that the phase monitoring relay is satisfied.

      ✓ Check: The meter shows right-hand rotation.

   6. Start and confirm direction. Start the compressor and watch the gauges. Stop at once if it sounds wrong or the pressures do not separate.

      ✓ Check: Within seconds suction pressure falls and discharge pressure rises, the current is normal and the compressor runs quietly.

8. 8

   A cylinder or evaporator sensor reads wrong and stops the cooling too early, or the control board is faulty.

   Remedy: Measure the sensor resistance against the table and replace a faulty sensor; contact the manufacturer for board faults.

   🛠 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 a sensor against a reference

   A temperature or pressure sensor that reads wrong makes the controller regulate wrong: wrong superheat, wrong defrost, false alarms. Compare it with a calibrated reference before changing settings or parts.

   1. Fit the reference next to the sensor. Fasten a calibrated thermometer probe beside the temperature sensor on the same pipe or in the same air stream, with heat-conducting paste and insulation. For a pressure sensor, connect a calibrated gauge to a service port at the same point in the circuit. Wear goggles and gloves when connecting to the refrigerant circuit.

      ✓ Check: The reference reading is steady for a few minutes.

   2. Compare with the controller reading. Read the live value of the sensor in the controller display or service tool at the same time as the reference.

      ✓ Check: The difference is within the tolerance given by the sensor or controller manufacturer (for a temperature sensor typically within about 1 K).

   3. Check offsets and sensor type. In the controller parameter list, check that the sensor type (e.g. NTC, PT1000, 0–10 V, 4–20 mA), the pressure range and any calibration offset match the fitted sensor. Record the original values before changing anything.

      ✓ Check: Sensor type, range and offset in the controller match the sensor data sheet.

   4. Measure the sensor resistance. Isolate and lock off the controller, disconnect the sensor and measure its resistance with a multimeter while the reference shows the temperature at the sensor. Compare with the manufacturer's resistance table. A PT1000 reads 1000 Ω at 0 °C; an ice-water bath gives a simple 0 °C check point.

      ✓ Check: The resistance matches the table value for the reference temperature; OL or 0 Ω means a broken or shorted sensor or cable.

   5. Check the sensor location and mounting. Inspect the pipe clamp or pocket: firm metal-to-metal contact, heat-conducting paste, insulation against the surrounding air and the correct position (e.g. evaporator outlet, not in the air stream of a fan).

      ✓ Check: The sensor sits firmly at the correct point and is insulated.

   6. Reconnect and confirm. Reconnect the sensor, restore power and compare the reading with the reference once more. Replace a sensor that is out of tolerance with one of the same type.

      ✓ Check: Controller and reference agree within the tolerance.

9. 9

   Mechanical fault in the refrigeration system: a compressor with poor valves, a blocked filter drier or expansion device, or a hot gas valve that leaks during freezing.

   Remedy: Check the compressor capacity, replace the filter drier or expansion device and check that the hot gas valve closes.

   🛠 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 whether the compressor pumps

   Low pressure difference, low current and poor capacity can mean a worn compressor, but often the cause is a bypass elsewhere. Compare measurements with the manufacturer's data and rule out other causes before you condemn the compressor.

   1. Measure in stable operation. Connect gauges to suction and discharge, and clamp thermometers on the suction line and on the discharge line close to the compressor, where the manufacturer specifies. Let the system run steadily for at least 15 minutes. Beware of the hot discharge pipe.

      ✓ Check: Pressures and temperatures are steady and noted together with the saturation temperatures.

   2. Measure current and voltage. Measure the supply voltage and the current in each phase with a true-RMS clamp meter (CAT III/IV, insulated probes, no loose clothing).

      ✓ Check: You have voltage and current for all phases; the phases are balanced.

   3. Compare with the compressor data. Enter the measured evaporating and condensing temperatures in the manufacturer's selection software or data sheet and read the expected current, capacity and discharge temperature.

      ✓ Check: Measured current and pressure difference are close to the data; clearly lower current at a low pressure difference suggests the compressor is not pumping.

   4. Rule out bypasses. Check the hot gas bypass valve, unloaders or capacity control solenoids, a digital scroll valve and any reversing valve: a pipe that is hot where it should be cold shows gas leaking back to suction.

      ✓ Check: All bypass paths are closed when they should be; otherwise repair them first and measure again.

   5. Check the internal relief valve. Many hermetic and scroll compressors have an internal pressure relief valve (IPR) between discharge and suction. If it has opened, suction pressure is high, discharge low, the shell is hot and the motor protection may trip. Find out why it opened (high pressure, blocked condenser) before restart.

      ✓ Check: The cause of an opened relief valve is found and removed, or the relief valve is ruled out.

   6. Check the valves after stop (reciprocating). On a reciprocating compressor, watch the gauges right after it stops. Discharge pressure falling fast while suction rises points to leaking discharge valves. Do not run scroll compressors into deep vacuum to test them; it damages them.

      ✓ Check: Pressures equalise slowly; fast equalisation confirms leaking valves.

   7. Decide. If the compressor still pumps too little with all other causes ruled out, plan a compressor replacement (see the guide on replacing a compressor). Record the measurements.

      ✓ Check: The decision is based on measurements compared with the manufacturer's data, and they are written down.

   Replace a filter drier

   Replace the filter drier after moisture, a compressor burnout, a restriction across the drier or whenever the circuit has been opened. Work on the refrigerant circuit requires F-gas certification; brazing is hot work.

   1. Isolate or recover the refrigerant. Pump down or close valves to isolate the drier section where the system allows, otherwise recover the refrigerant with a recovery unit into a marked recovery cylinder. Break the vacuum with dry nitrogen to just above atmospheric pressure before opening. With A2L/A3 refrigerants purge with nitrogen and check with a gas detector.

      ✓ Check: The section reads slightly above 0 bar(g) on nitrogen and the pressure does not rise (no refrigerant left).

   2. Choose the right drier. Use a drier of the same size or larger, with connections and capacity for the refrigerant. After a burnout or acid in the oil use a burnout (acid-removing) type and plan to replace it again after the clean-up; after moisture choose one with ample water capacity.

      ✓ Check: The new drier matches the refrigerant, size and situation, and its arrow follows the flow direction.

   3. Cut out the old drier. Cut the pipes with a pipe cutter (never a hacksaw, which leaves filings) and deburr with the pipe end held downward. Keep the new drier capped until just before fitting.

      ✓ Check: Pipe ends are round, clean and burr-free.

   4. Braze with nitrogen flowing. Get a fire permit, have an extinguisher at hand and remove flammable material. Purge a low flow of dry nitrogen through a regulator while brazing, and cool the drier body with a wet cloth so the desiccant is not overheated. Never use oxygen or compressed air. Flare driers are fitted with torque spanners instead.

      ✓ Check: Clean joints with full penetration, and no black oxide scale inside the pipe ends.

   5. Pressure test with nitrogen. Pressurise with dry nitrogen through a regulator to the test pressure for the system, never above PS, and leak test the new joints.

      ✓ Check: The pressure holds and no leak is found at the joints.

   6. Evacuate, charge and record. Evacuate with a micron gauge to the manufacturer's level (commonly below 500 micron/0.67 mbar), close off the pump and check that the vacuum holds. Charge the specified amount by weight and record the work and refrigerant amounts in the logbook.

      ✓ Check: The vacuum holds, the charge is weighed in and the logbook entry is complete.

   Check a solenoid valve (liquid line or hot gas)

   A solenoid valve that does not open starves the evaporator (low pressure, warm room); one that does not close lets refrigerant through when it should not (pump-down fails, flooding, or hot gas leaking into the evaporator). Check the coil first, then the valve itself.

   1. Find out whether the valve should be open. Read in the controller or the wiring diagram when the valve is energised (for example with cooling demand, during pump-down or during hot gas defrost). Compare with what the system does right now.

      ✓ Check: You know whether the valve should be open or closed at this moment.

   2. Check that the coil gets voltage. Measure the voltage across the coil terminals when the valve should be open. Hold a steel screwdriver blade near (not touching) the top of the coil: a live coil pulls it slightly. Check that the coil voltage on its label matches the supply.

      ✓ Check: The coil has the rated voltage (label) when the valve should be open; if not, the fault is upstream: thermostat, controller output, contactor, fuse or wiring.

   3. Check the coil itself. Isolate and lock off, prove dead, and disconnect the coil. Measure its resistance and compare with the manufacturer's value; look for a burnt smell, discolouration or a cracked coil. Make sure the coil is the right type for the valve body and sits fully down on the armature tube with its nut tight.

      ✓ Check: Coil resistance matches the data (an open circuit or a very low value means a faulty coil), and the coil is the right one and correctly fitted.

   4. Check that the valve opens. With the coil energised and the system running, measure the temperature on both sides of the valve with clamp thermometers. An open valve has (almost) the same liquid temperature on both sides; a clear temperature drop or frost after the valve means it is not opening fully or is restricted. Check the flow direction arrow on the valve body.

      ✓ Check: Little or no temperature difference across the valve when it should be open, and it is fitted in the direction of the arrow.

   5. Check that the valve closes. De-energise the coil (or let the controller close it) and watch what happens: on a pump-down system the suction pressure must fall and the compressor must stop on the low pressure switch and stay off; a hot gas valve must leave the line after it cool during the freeze or cooling cycle.

      ✓ Check: The system pumps down and stays down, or the line after a hot gas valve stays cool; a valve that leaks through must be repaired or replaced.

   6. Repair or replace. A faulty coil can be changed without opening the circuit. If the valve body leaks or sticks, opening the circuit is work for certified personnel: recover the refrigerant, replace the valve (or its internal parts) with nitrogen flowing while brazing, pressure test with dry nitrogen, evacuate and charge by weight. Protect the valve from heat while brazing as the manufacturer describes.

      ✓ Check: The valve opens and closes as it should, there is no leak at the new joints, and the work is recorded in the logbook where the refrigerant rules require it.