Compressor short cycling

Troubleshooting · Applies to: Direct expansion refrigeration system · Heat pump and air conditioning · Liquid chiller (water or brine) · Cold rooms with several evaporators

Short cycling step by step: trips on low or high pressure or motor protection, small thermostat differential and control faults.

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

Many starts per hour wear the compressor, contactor and motor, and manufacturers specify a maximum number of starts per hour ^[1]. Find out which function stops the compressor each time: the controller's alarm log or the pressure switch indication usually shows it.

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

Count the starts per hour and note why the compressor stops: thermostat, alarm or safety device. Measure the voltage along the safety chain when it stops: where the voltage disappears is where the fault is.

📏 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
The suction pressure drops below the cut-out shortly after start.
Remedy: Check the pressure switch differential and follow the low-pressure troubleshooting. On a pump-down system: if the compressor restarts soon after stopping, check that the liquid solenoid valve closes tightly.
🛠 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 a pressure switch or transducer
High and low pressure switches protect the compressor and the system. Check that they cut out and cut in at their settings against a calibrated gauge, and that transducers send the correct signal. Never bypass a pressure switch.
1. Connect a calibrated gauge. Connect a calibrated gauge or digital manifold to a service port on the same side and as close as possible to the switch or transducer. Wear goggles and gloves; with A2L/A3 refrigerants keep ignition sources away.
  ✓ Check: The gauge reads a stable pressure close to the switch.
2. Read the settings. Note cut-out, cut-in (or differential) and reset type (automatic or manual) from the switch scale or the controller. The HP setting must be below the safety valve set pressure and the system PS.
  ✓ Check: You know what each switch should do and the HP setting is below the safety valve pressure.
3. Test the low pressure switch. Slowly close the liquid line valve (pump down) while watching the gauge and the switch contact or the controller input. Do not let the compressor run into deep vacuum.
  ✓ Check: The switch opens at its cut-out setting within the manufacturer's tolerance and closes again at its cut-in.
4. Test the high pressure switch. Where it can be done safely, reduce the condenser airflow step by step while watching the gauge. Stop immediately if the pressure reaches the setting without a trip. On CO2 systems, or where raising the pressure is not safe, test the switch off the system with nitrogen and a regulator instead.
  ✓ Check: The switch trips at its setting within tolerance and well below the safety valve pressure.
5. Check the transducer signal. Measure the output (e.g. 0.5–4.5 V or 4–20 mA) at the controller input and convert it with the transducer range to pressure.
  ✓ Check: The calculated pressure agrees with the reference gauge within the transducer's tolerance.
6. Restore and record. Open the valves fully, restore airflow, reset any manual reset device and write the measured cut-out and cut-in points in the service report. Replace a switch that does not trip at its setting.
  ✓ Check: The system runs normally and the measured values are documented.
Check the pump-down function
In pump-down the liquid solenoid valve closes and the compressor pumps the low side down until the low pressure switch stops it. If the valve leaks or the switch is set wrong, the compressor short cycles or liquid migrates to the crankcase.
1. Connect gauges. Connect gauges to the suction and discharge service ports with short hoses and minimal refrigerant loss. Note the low pressure switch cut-out and cut-in settings from the switch or the controller.
  ✓ Check: Both gauges show stable operating pressures and the switch settings are noted.
2. Start the pump-down. Make the thermostat or controller stop the cooling call (raise the setpoint or open the thermostat contact) so the liquid solenoid valve is de-energised.
  ✓ Check: The coil voltage on the solenoid valve drops to 0 V (measured with a CAT III/IV meter) and the valve clicks closed.
3. Watch the suction pressure fall. Watch the suction gauge while the compressor keeps running and pumps refrigerant into the condenser and receiver.
  ✓ Check: The suction pressure falls steadily towards the cut-out setting; it does not stop falling well above it.
4. Check the low pressure cut-out. Note the pressure at which the compressor stops and compare it with the setting.
  ✓ Check: The compressor stops at the set cut-out pressure, within the accuracy of your gauge.
5. Check that the solenoid valve holds. With the compressor stopped, watch the suction pressure for several minutes and feel or measure the pipe temperature after the solenoid valve. A slow rise as the evaporator warms up is normal; a fast rise, or a cold pipe or frost after the valve, means the valve is passing liquid.
  ✓ Check: The suction pressure rises only slowly and the pipe after the valve is not getting cold.
6. Check the restart. Restore the cooling call. The solenoid valve should open, the suction pressure rise above the cut-in and the compressor start. Without a cooling call the compressor must not restart on its own within a short time; check the anti-short-cycle timer in the controller.
  ✓ Check: The compressor restarts only when cooling is called for and does not cycle on the low pressure switch alone.
Continue with: System trips on low pressure →
2
The pressure switch differential is too small, or the solenoid valve leaks during pump-down so the low pressure rises and the compressor restarts.
Remedy: Set the differential according to the manufacturer. Check that the solenoid valve closes tightly during pump-down.
🛠 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 a pressure switch or transducer
High and low pressure switches protect the compressor and the system. Check that they cut out and cut in at their settings against a calibrated gauge, and that transducers send the correct signal. Never bypass a pressure switch.
1. Connect a calibrated gauge. Connect a calibrated gauge or digital manifold to a service port on the same side and as close as possible to the switch or transducer. Wear goggles and gloves; with A2L/A3 refrigerants keep ignition sources away.
  ✓ Check: The gauge reads a stable pressure close to the switch.
2. Read the settings. Note cut-out, cut-in (or differential) and reset type (automatic or manual) from the switch scale or the controller. The HP setting must be below the safety valve set pressure and the system PS.
  ✓ Check: You know what each switch should do and the HP setting is below the safety valve pressure.
3. Test the low pressure switch. Slowly close the liquid line valve (pump down) while watching the gauge and the switch contact or the controller input. Do not let the compressor run into deep vacuum.
  ✓ Check: The switch opens at its cut-out setting within the manufacturer's tolerance and closes again at its cut-in.
4. Test the high pressure switch. Where it can be done safely, reduce the condenser airflow step by step while watching the gauge. Stop immediately if the pressure reaches the setting without a trip. On CO2 systems, or where raising the pressure is not safe, test the switch off the system with nitrogen and a regulator instead.
  ✓ Check: The switch trips at its setting within tolerance and well below the safety valve pressure.
5. Check the transducer signal. Measure the output (e.g. 0.5–4.5 V or 4–20 mA) at the controller input and convert it with the transducer range to pressure.
  ✓ Check: The calculated pressure agrees with the reference gauge within the transducer's tolerance.
6. Restore and record. Open the valves fully, restore airflow, reset any manual reset device and write the measured cut-out and cut-in points in the service report. Replace a switch that does not trip at its setting.
  ✓ Check: The system runs normally and the measured values are documented.
Check the pump-down function
In pump-down the liquid solenoid valve closes and the compressor pumps the low side down until the low pressure switch stops it. If the valve leaks or the switch is set wrong, the compressor short cycles or liquid migrates to the crankcase.
1. Connect gauges. Connect gauges to the suction and discharge service ports with short hoses and minimal refrigerant loss. Note the low pressure switch cut-out and cut-in settings from the switch or the controller.
  ✓ Check: Both gauges show stable operating pressures and the switch settings are noted.
2. Start the pump-down. Make the thermostat or controller stop the cooling call (raise the setpoint or open the thermostat contact) so the liquid solenoid valve is de-energised.
  ✓ Check: The coil voltage on the solenoid valve drops to 0 V (measured with a CAT III/IV meter) and the valve clicks closed.
3. Watch the suction pressure fall. Watch the suction gauge while the compressor keeps running and pumps refrigerant into the condenser and receiver.
  ✓ Check: The suction pressure falls steadily towards the cut-out setting; it does not stop falling well above it.
4. Check the low pressure cut-out. Note the pressure at which the compressor stops and compare it with the setting.
  ✓ Check: The compressor stops at the set cut-out pressure, within the accuracy of your gauge.
5. Check that the solenoid valve holds. With the compressor stopped, watch the suction pressure for several minutes and feel or measure the pipe temperature after the solenoid valve. A slow rise as the evaporator warms up is normal; a fast rise, or a cold pipe or frost after the valve, means the valve is passing liquid.
  ✓ Check: The suction pressure rises only slowly and the pipe after the valve is not getting cold.
6. Check the restart. Restore the cooling call. The solenoid valve should open, the suction pressure rise above the cut-in and the compressor start. Without a cooling call the compressor must not restart on its own within a short time; check the anti-short-cycle timer in the controller.
  ✓ Check: The compressor restarts only when cooling is called for and does not cycle on the low pressure switch alone.
3
Flowchart C
The thermostat differential is too small, the sensor is in the cold air stream or the system is oversized for the load.
Remedy: Increase the differential or the minimum run and off times and move the sensor. For an oversized system: capacity or speed control.
🛠 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 controller settings and alarm log
Many faults that look like hardware faults are wrong settings or alarms that keep repeating. Read the alarm log and compare the settings with the manufacturer's parameter list before you change anything.
1. Read the alarm log. Open the alarm menu with the keypad or service tool and note every recent alarm code with date and time. Look up each code in the manufacturer's manual.
  ✓ Check: You have a list of alarms with times and know what each code means.
2. Check the clock. Check the controller's date and time. A wrong clock shifts scheduled defrosts and night setback and makes the alarm log misleading.
  ✓ Check: The controller clock shows the correct local date and time.
3. Record all settings before changing anything. Write down, photograph or export setpoints, differentials, neutral zone, minimum run and off times, anti-short-cycle timer, defrost interval and duration, and the operating mode.
  ✓ Check: The service report holds a complete copy of the original settings.
4. Compare with the parameter list. Compare each value with the manufacturer's parameter list and the plant documentation. Look in particular for a differential that is too small (short cycling), timers set to zero and setpoints that do not match the application.
  ✓ Check: Every deviation is noted with the original and the recommended value.
5. Check the safety limits. Compare low and high pressure cut-outs and temperature limits in the controller with the manufacturer's values. Never set a safety limit beyond the manufacturer's values, and the high pressure cut-out must stay below the safety valve set pressure.
  ✓ Check: All safety limits are within the manufacturer's values.
6. Change one value at a time and test. Correct one setting at a time, check the operating mode, and let the system run long enough to see the effect. Record every change in the service report.
  ✓ Check: The system runs as expected and the alarm does not return.
Check capacity control
Capacity control makes the plant follow the load. If it does not work, suction pressure swings, compressors short cycle and wear out.
1. Read the controller settings. Note the suction pressure (or temperature) setpoint, neutral zone, number of steps, speed range and the minimum run and off timers. Compare the timers with the compressor maker's limit for starts per hour.
  ✓ Check: Settings are noted and the timers respect the maker's start limit.
2. Check the control sensor. Compare the suction pressure transducer that the controller uses with a calibrated gauge at the same point.
  ✓ Check: The controller reading agrees with the gauge.
3. Follow the control over time. Log suction pressure, capacity steps or speed and compressor starts over at least 30 minutes, or read the controller's trend log.
  ✓ Check: Suction pressure stays within the neutral zone and steps change in order without rapid on-off.
4. Test each step in manual mode. In the controller's manual or test mode, switch each unloader or capacity solenoid. Measure coil voltage with a CAT III/IV meter and watch current and suction pressure. Check in the manufacturer's data whether an energised coil loads or unloads.
  ✓ Check: Each step gives a clear change in current and suction pressure in the expected direction.
5. Check speed and digital control. For an inverter compressor, check that the speed follows the controller signal. For a digital scroll, check the modulation signal and the solenoid.
  ✓ Check: Speed or modulation follows the demand over the whole range.
6. Count starts. Count compressor starts per hour from the log and compare with the manufacturer's maximum.
  ✓ Check: Starts per hour are below the manufacturer's limit.
4
Flowchart B
A safety device trips because of high pressure, an overheated motor or overcurrent.
Remedy: If it stops on high pressure, follow the high-pressure troubleshooting. If the motor protection trips, follow the motor protection troubleshooting: voltage, current and starts per hour.
🛠 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.
Check motor protection setting and trips
Motor protection stops the compressor or fan before the motor burns. A wrong setting causes needless trips or no protection at all, and a protection that is reset again and again without finding the cause destroys the motor.
1. Read the trip and the alarm log. Note which protection has tripped (overload relay, motor protection breaker, electronic module or inverter) and read the alarm log in the controller for time and number of trips.
  ✓ Check: You know which device tripped, when and how often.
2. Check the setting against the nameplate. Compare the current setting of the overload relay or motor protection breaker with the value the compressor or motor manufacturer gives (for example the maximum continuous current on the nameplate or in the data sheet). Never set it higher than that value.
  ✓ Check: The setting agrees with the manufacturer's value.
3. Read the electronic protection module. On compressors with a thermistor protection module (for example Kriwan INT69), read any diagnosis LED or flash code with the module's manual. Check that its supply voltage is correct.
  ✓ Check: The module shows normal, or the code is identified in the manual.
4. Measure current in operation. With the protection reset and the cause not obviously dangerous, start the unit and measure the current on every phase with a clamp meter (CAT III/IV, insulated, no loose clothing). Compare with the nameplate and check that the phases are balanced.
  ✓ Check: The current is below the protection setting and nearly equal on all phases.
5. Count the starts. Count starts per hour from the controller log or by watching. Compare with the maximum starts per hour in the compressor data. Too many starts point to short cycling (setpoint, differential or low pressure switch).
  ✓ Check: The number of starts is within the compressor manufacturer's limit.
6. Find the cause before resetting again. Look for the cause of the trip: high condensing pressure, low or unbalanced voltage, a lost phase, a mechanical fault or a winding fault. Isolate and lock off before opening terminals. Reset only when the cause is found and fixed.
  ✓ Check: The cause is found and corrected, and the unit runs without new trips.
Continue with: System trips on high pressure →
5
Flowchart D
Loose connections, a faulty contactor or a controller that restarts after alarms.
Remedy: Check the contactor, terminals and control signals with the system isolated, and go through the alarm log.
🛠 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.
Safe isolation and lock-off
Before you open a panel or touch electrical parts, isolate every supply, lock it off and prove that the circuit is dead. Electrical work is for qualified personnel only.
1. Identify all supplies. Use the wiring diagram to find every supply: main feed, separate control supply, heaters, alarm and UPS supplies, and inverters that can feed back.
  ✓ Check: You know every isolation point for the equipment you will work on.
2. Switch off, lock and tag. Switch each isolator to OFF, fit your own padlock and attach a tag with your name and date. Keep the key on you.
  ✓ Check: Every isolator is locked in OFF and cannot be switched on by someone else.
3. Prove the tester. Check the two-pole voltage tester (EN 61243-3) on a proving unit or a known live source.
  ✓ Check: The tester shows the voltage of the known source.
4. Prove dead. Measure phase to phase, each phase to neutral and each phase to earth at the point of work, on both line and load side.
  ✓ Check: The tester shows 0 V on every combination.
5. Prove the tester again. Check the tester on the proving unit once more, to be sure it did not fail during the measurement.
  ✓ Check: The tester again shows the voltage of the known source.
6. Deal with stored energy. On an inverter, wait the discharge time printed on the drive and measure the DC bus. Discharge start and run capacitors through a resistor of about 20 kΩ, 5 W with insulated leads, never with a screwdriver.
  ✓ Check: 0 V DC on the DC bus and across every capacitor.
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 controller settings and alarm log
Many faults that look like hardware faults are wrong settings or alarms that keep repeating. Read the alarm log and compare the settings with the manufacturer's parameter list before you change anything.
1. Read the alarm log. Open the alarm menu with the keypad or service tool and note every recent alarm code with date and time. Look up each code in the manufacturer's manual.
  ✓ Check: You have a list of alarms with times and know what each code means.
2. Check the clock. Check the controller's date and time. A wrong clock shifts scheduled defrosts and night setback and makes the alarm log misleading.
  ✓ Check: The controller clock shows the correct local date and time.
3. Record all settings before changing anything. Write down, photograph or export setpoints, differentials, neutral zone, minimum run and off times, anti-short-cycle timer, defrost interval and duration, and the operating mode.
  ✓ Check: The service report holds a complete copy of the original settings.
4. Compare with the parameter list. Compare each value with the manufacturer's parameter list and the plant documentation. Look in particular for a differential that is too small (short cycling), timers set to zero and setpoints that do not match the application.
  ✓ Check: Every deviation is noted with the original and the recommended value.
5. Check the safety limits. Compare low and high pressure cut-outs and temperature limits in the controller with the manufacturer's values. Never set a safety limit beyond the manufacturer's values, and the high pressure cut-out must stay below the safety valve set pressure.
  ✓ Check: All safety limits are within the manufacturer's values.
6. Change one value at a time and test. Correct one setting at a time, check the operating mode, and let the system run long enough to see the effect. Record every change in the service report.
  ✓ Check: The system runs as expected and the alarm does not return.

Checks from the manufacturers’ manuals (15)

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

Bitzer VARIPACK FDU+/FKU+: most faults reset themselves up to five times after a delay (300 s ex works); after five faults within five intervals or five minutes an external reset is needed.^[2]
Copeland 20–40 ton scroll module: any run shorter than 3 minutes counts as a short cycle; it warns after 48 in 24 hours, or locks out at the user-set count when that DIP switch is on.^[3]
Danfoss VLT FC 103: short-cycle protection (parameters 22-75 and 22-76) holds the compressor back and shows warning 96 Start delayed or 97 Stop delayed, which is normal, not a fault.^[4]
Temperzone UC7/UC8: HOLd means a safety timer is holding the compressor on or off; after an HP or LP trip it waits 3 minutes before retrying, so wait before judging a no-start.^[5]
Castel pilot-operated solenoid valves (diaphragm/piston, e.g. 1070, 1040) need a minimum pressure difference of about 0.05–0.07 bar to open and seal; near zero differential use a direct-acting valve (1020/1028).^[6]
Copeland ZSH/YSH/ZFH/YFH scrolls: Scroll compressor: the internal discharge check valve can leak back after stop, so high-pressure gas re-expands into the suction side and the low-pressure switch resets and restarts the compressor. A sensor mounted right at the suction inlet and fixed (non-adjustable) switches make it worse. Widen the differential, add a 3-minute delay, and on pump-down systems fit a separate external check valve.^[7]
Carlyle 06D/06E/06CC; Dorin semi-hermetic compressors: The capillary or tube to the low-pressure switch is clogged, kinked or crimped, so the switch reacts erratically.^[8]
Copeland semi-hermetic/scroll on Hussmann parallel racks: First find which device is cycling: motor protector, thermostat, LP or HP switch. For HP cycling check that the discharge service valve is fully back-seated; never front-seat the suction service valve in a way that isolates the LP switch from the compressor.^[9]
Danfoss Maneurop MT/MTZ; Copeland scroll; Hussmann CO2 racks: Starts per hour that makers allow: Danfoss MT/MTZ at most 12 (6 with soft start) with a 6-minute anti-short-cycle timer; Copeland scroll at most about 10; Hussmann CO2 racks at most 6 per compressor. The minimum run time must also be long enough for the oil to come back (about 5 minutes on compact circuits).^[10]
Copeland Digital Compressor Controller: A low-pressure switch that cuts out and in within seconds can be read by compressor electronics as a locked rotor (Copeland digital controller: four starts within 20 s) and the compressor is locked out until the 24 V supply is cycled. Widen the LP differential or add a delay before blaming the compressor.^[11]
Heatcraft Beacon II controls: The compressor stops without any error code when the 24 V control voltage drops as the contactor pulls in: low supply voltage, a short in the field wiring to the condensing unit contactor, or a failing contactor holding coil. Measure the 24 V at the board while the contactor closes.^[12]
Beverage-Air DW and UCF cabinets: An empty cabinet has almost no thermal mass, so the air temperature reaches the set point quickly and the compressor starts and stops often.^[13]
Fujitsu split air conditioners and heat pumps: Before replacing a Fujitsu PCB for a sensor fault, measure the thermistor. On the older UK range at 20 °C: air sensors about 13 kΩ, indoor pipe sensor about 63 kΩ, outdoor pipe sensor about 6 kΩ and discharge sensor about 395 kΩ.^[14]
Hitachi RUA-NP4ATS…RUA-NP10ATS self-contained air conditioners (R410A): Both pressure switches on the RUA-NP reset automatically (HP back at 3.2 MPa, LP back at 0.70 MPa), so a unit that trips repeatedly can look like short cycling. Read the alarm history: hold SW1 on the PCB for more than 3 s until SEG1 flashes AL, then step through the last five codes with single presses; repeated 45 or 47 codes show which switch is acting. Holding SW1 for more than 5 s erases the history.^[15]
Daikin VRV, VRV-III and VRV-WII systems (RXYQ, REYQ, RWEYQ) with FXxQ indoor units: Factory thermostat differential on VRV indoor units is 1 K (1.8 °F): thermostat-off at set point −1 K in cooling and +1 K in heating, adjustable to 0.5 K by field setting (a smaller differential gives more frequent cycling). Ceiling cassettes in heating use the unit thermostat value lowered by 2 K (3.6 °F). In dry mode the fan stops for 6 minutes at thermostat-off and then returns at low speed.^[16]

📝 Fill in a service report

Terms in this article

Low-pressure switch High-pressure switch

Sources

Danfoss Ref Tools – Troubleshooter: compressor
Bitzer – VARIPACK external frequency inverters, operating instructions CB-100-2 (06.2018)
Copeland – Compressor electronics communications for 20 to 40 ton scroll compressors, AE8-1384 R9 (July 2026)
Danfoss – VLT Refrigeration Drive FC 103 instruction manual, MG16E322 (2014-04-10)
Temperzone – UC8 operation manual air-to-air units, issue 4 (21 April 2017)
Castel – Solenoid Valves Handbook, VS-ED 01/2017-ENG (2017)
Copeland – Application bulletin AE4-1472 R2, ZSH/YSH/ZFH/YFH refrigeration scrolls (May 2024), p. 9
Carlyle – Service Guide 020-611, 06D/06E/06CC semi-hermetic compressors + Dorin – Operating instructions semi-hermetic compressors (1LTG664-15.1), p. 28 (item 4) | p. 25 (item 2)
Hussmann – Parallel Rack Installation & Operation, P/N 0427598_E, p. 7-2 (Copeland form 2004CC-126)
Danfoss – Maneurop MT/MTZ Application Guide AB196386425654en-011901 (2026.07) | Copeland – Application Guidelines, heat pump scroll XHV variable speed (AGL_HP_VS_XHV_EN_Rev00) | Hussmann – Transcritical CO2 Rack Installation & Operation, PN 3182569_G, Danfoss: p. 48 | Copeland: p. 26 | Hussmann: p. 72
Copeland – Bulletin AE8-1328 R7 (Sept 2024), Digital Compressor Controller, p. 11 (AE8-1328 R7)
Heatcraft – Beacon II Installation and Operation Manual H-IM-79G, Beacon II Troubleshooting Guide, E6, p. 25
Beverage-Air – Installation and operating instructions DW deep well, 809-184A + Beverage-Air – Installation and operating instructions UCF freezers, 809-174A, DW p. 21; UCF p. 20
Fujitsu – Fujitsu Trouble Shooting Guide (UK edition, undated, R22 era), p. 4, Sensor Resistances (undated; copy archived 2026-11-02)
Hitachi – Self-Contained Air Conditioners RUA-NP4ATS…RUA-NP10ATS (R410A), Installation, Operation and Maintenance Instructions Manual 65MP3197-A2 (Bosch Home Comfort Philippines); undated, PDF file created 2025, 3.3.5 Alarm History Check, p. 6; 6.5 Safety and Control Device Setting, p. 12
Daikin AC (Americas) – VRV Service & Troubleshooting, Participant Guide: VRV Systems Basic Operation Guide, Engineering Data EGVUSE09-07C (09/2007), with VRV III service manual navigation and Service Checker Type III workshop slides, 4.1.2 Thermostat Control in Normal Operation, p. 10; 4.1.3 Dry Mode, p. 11

Compressor short cycling

Confirm the fault first

Troubleshoot step by step

Flowchart

Causes, most likely first

Test a pressure switch or transducer

Check the pump-down function

Test a pressure switch or transducer

Check the pump-down function

Check controller settings and alarm log

Check capacity control

Measure voltage and current under load

Check motor protection setting and trips

Safe isolation and lock-off

Test a contactor

Check controller settings and alarm log

Checks from the manufacturers’ manuals (15)

Service report

Terms in this article

Sources