GENERAL AIRSTAGE | Technical Reference
MultiPower Chiller & Heat Pump
Service, hydronic, electrical, controller and defrost reference
For GENERAL AIRSTAGE multi-scroll liquid chiller and reversible heat-pump applications.
Purpose: This article consolidates key service-training information for MultiPower chiller and heat-pump systems, including configuration identification, hydronic requirements, electrical checks, BMS interfaces, UNICO controller operation, compressor timers and defrost control.
Safety: Chiller service work includes mains voltage, pressurised refrigerant circuits and pressurised hydronic systems. Work must only be carried out by appropriately qualified personnel. Always use the wiring diagram and installation/operation documentation supplied with the specific unit before changing wiring or parameters.
1. Product variants and factory-fitted options
| Variant | Configuration |
|---|---|
| CHA/K | Cooling only |
| CHA/K/WP | Reversible heat pump |
| CHA/K/SSL | Super-silenced cooling only |
| CHA/K/WP/SSL | Super-silenced reversible heat pump |
| Code | Factory-fitted option | Code | Factory-fitted option |
|---|---|---|---|
| SL | Unit silencing | RFM | Cooling-circuit shut-off valve on discharge line |
| CT | Condensing control down to 0°C | CC | Condensing control down to -20°C |
| BT | Low-water-temperature kit | EC | EC inverter fans |
| ECH | EC inverter fans with high available static pressure | DS | Desuperheater |
| RT | Total heat recovery | TX | Coil with pre-coated fins |
| EW | External water connections | PS | Single circulating pump |
| PSI | Inverter single circulating pump | PD | Double circulating pump |
| PDI | Inverter double circulating pump | SS | Soft start |
| IS | Modbus RTU, RS485 serial interface | IST | Modbus TCP/IP, Ethernet port |
| ISB | BACnet MS/TP, RS485 serial interface | ISBT | BACnet/IP, Ethernet port |
| ISL | LonWorks, FTT-10 serial interface | ISS | SNMP, Ethernet port |
| IAV | Remote set-point, 0–10 V signal | IAA | Remote set-point, 4–20 mA signal |
| IAS | Remote signal for second set-point activation | IDL | Demand limit from digital input |
Exact operating envelopes depend on the selected unit configuration and fitted options. Confirm the unit selection data and the specific installation manual before operating outside standard water or ambient conditions.
2. Hydronic system requirements
Water filtration
- Install the water filter on the machine inlet side.
- Square-mesh filter maximum opening: 0.8 mm up to DN80.
- Square-mesh filter maximum opening: 1.6 mm up to DN150.
- Filters must be cleaned periodically.
Minimum system water volume
Cooling-only version
M > 9.45 × k × n / N × (Qf − q)
Heat-pump version
M > 9.45 × k × n / N × (Qt − q) + 2.37 × (Qt − q)
| Symbol | Meaning |
|---|---|
| M | Minimum water content (L) |
| k | Factor accounting for the water-temperature difference between evaporator/condenser inlet and outlet |
| n | Partition coefficient: n=1 up to 4 compressors; n=2 for units with more than 4 compressors |
| N | Number of compressors |
| Qf | Cooling capacity (kW) |
| Qt | Heating capacity (kW) |
| q | Permanent thermal load in the system (kW); use q=0 if unknown |
| ΔT (K) | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|
| k | 1 | 1 | 1 | 1.05 | 1.10 | 1.15 | 1.20 | 1.25 |
- For process applications, the source recommends 50% higher water content to stabilise outlet temperature.
- If circuit volume is insufficient, add an inertial storage/buffer tank so total system volume reaches the calculated requirement.
Water quality guidance
Water quality is critical to unit performance and heat-exchanger life. The source rates compatibility for AISI 316L and copper using: 1 = good corrosion resistance, 2 = corrosion may occur when multiple adverse factors are present, 3 = use not recommended.
| Parameter | Range | AISI 316L | Copper |
|---|---|---|---|
| pH | <6 | 2 | 2 |
| 6–7.5 | 2 | 2 | |
| 7.5–9 | 1 | 1 | |
| >9 | 1 | 2 | |
| Alkalinity (HCO3) | <70 mg/L | 1 | 2 |
| 70–300 mg/L | 1 | 1 | |
| >300 mg/L | 1 | 2 | |
| Sulphate (SO4²−) | <70 mg/L | 1 | 1 |
| 70–300 mg/L | 1 | 3 | |
| >300 mg/L | 1 | 3 | |
| Alkalinity / sulphate | HCO3− / SO4²− >1 | 1 | 1 |
| HCO3− / SO4²− <1 | 1 | 3 | |
| Electrical conductivity | <10 µS/cm | 1 | 2 |
| 10–500 µS/cm | 1 | 1 | |
| >500 µS/cm | 1 | 2 | |
| Ammonium (NH4) | <2 mg/L | 1 | 1 |
| 2–20 mg/L | 1 | 2 | |
| >20 mg/L | 1 | 3 | |
| Free chlorine (Cl2) | <1 mg/L | 1 | 1 |
| 1–5 mg/L | 3 | 1 | |
| >5 mg/L | 3 | 3 | |
| Hydrogen sulphide (H2S) | <0.05 mg/L | 1 | 1 |
| >0.05 mg/L | 1 | 3 | |
| Free carbon dioxide (CO2) | <5 mg/L | 1 | 1 |
| 5–20 mg/L | 1 | 2 | |
| >20 mg/L | 1 | 3 | |
| Nitrate (NO3) | <100 mg/L | 1 | 1 |
| >100 mg/L | 1 | 2 | |
| Iron (Fe) | <0.2 mg/L | 1 | 1 |
| >0.2 mg/L | 1 | 2 | |
| Aluminium (Al) | <0.2 mg/L | 1 | 1 |
| >0.2 mg/L | 1 | 2 | |
| Manganese (Mn) | <0.1 mg/L | 1 | 1 |
| >0.1 mg/L | 1 | 2 |
Filling a hydronic-kit system
- Ensure the main switch is OFF before work begins.
- If the hydronic kit is fitted, confirm the pump drain shut-off valve is closed.
- Confirm drain valves are closed and air-vent valves are open.
- Open the water-system shut-off valves and begin filling.
- When water reaches the vent valves, close the vents and bring system pressure to approximately 1–1.5 bar.
- The referenced safety-valve calibration is 6 bar.
- After pressure stabilises, close the fill valve and check all joints for leaks.
Flow switch and pump sequence
- The chiller must only operate when water flow is proven.
- If an external flow switch is required, the source identifies connection at X2 41A–42A.
- Remote circulating-pump control is shown from the controller at 115–116, 230 V AC output.
- The pump must start before the chiller and stop after the chiller. Recommended minimum run-on delay: 60 seconds.
3. Freeze protection and glycol
If the system cannot be drained during periods where freezing is possible, or operation is required with water temperatures below 5°C, the source specifies the use of ethylene glycol. Glycol changes system capacity, absorbed power, water flow and pressure drop, so correction factors must be applied.
| Glycol | 10% | 20% | 30% | 40% | 50% |
|---|---|---|---|---|---|
| Tc – Freezing temperature (°C) | -4.5 | -9.5 | -15.5 | -21.5 | -32.5 |
| CQ – Cooling-capacity factor | 0.975 | 0.953 | 0.931 | 0.914 | 0.882 |
| CP – Electrical-power factor | 0.998 | 0.995 | 0.990 | 0.985 | 0.975 |
| CG – Water-flow factor | 1.01 | 1.04 | 1.08 | 1.14 | 1.20 |
| Cp – Pressure-drop factor | 1.05 | 1.13 | 1.21 | 1.26 | 1.32 |
Antifreeze parameter (AIS): Factory setting shown is 3.0°C. When glycol is used, the source states the AIS value must be set to the fluid freezing temperature plus 6 K. The minimum allowable AIS setting must correspond with the glycol percentage in the unit selection data. When an ICE alarm is active, the water pumps will start.
The source recommends checking glycol concentration with a refractometer or equivalent instrument.
4. Electrical, BMS and control interfaces
Three-phase supply and phase monitor
- Verify L1, L2 and L3 against the unit data plate. The source allows a voltage tolerance of ±5%.
- Check fuse-holder caps and all power connections inside the electrical enclosure for correct tightness.
- Where crankcase heaters are fitted, confirm operation. The source check is approximately 10–15°C above ambient at the compressor base.
- For three-phase versions, verify correct rotation. The source states clockwise when viewed from the motor fan side; if incorrect, swap any two phase conductors below the main switch.
- 3-phase relay shown: DPA51CM (RF1). LED indication: Green = power ON; Yellow = 3-phase sequence OK.
Compressor oil-heating timer
The controller includes a 180-minute compressor oil-heating delay on initial energisation. Do not remove power during the countdown: the timer will restart at 180 minutes. If a normal-operation power failure exceeds 60 minutes, the timer restarts from 180 minutes. The source states this timer function cannot be deactivated.
The BMS digital-control diagram associates terminals 7–8 with the compressor oil-heating timer bridge. Confirm the unit-specific wiring diagram before altering any bridge or input.
BMS / remote control
| Terminal group | Function shown in training material |
|---|---|
| X2 | Remote On/Off; Emergency; general alarm contact (free voltage) |
| X5 | Remote display (CR option). For CR installation, the source instructs removal of the 120 Ω electrical resistor. |
Electronic expansion-valve control
The training material shows an EKE-1D / EKE-2U based electronic expansion-valve control arrangement. Key items identified are:
- MD: EKE-1D driver
- BC1: battery charger / backup module
- ALD1: AC/DC converter
- TP3: suction pressure sensor
- SVT1: suction temperature sensor
- VT1: electronic thermostatic valve
For the EKE-2U backup arrangement, the source shows ALD1 output adjusted to 24 V DC and the backup module connected to the valve supply. Load-switch position is dependent on valve type and the number of valves; use the unit wiring documentation before changing the switch position.
Main internal service items
| Area | Items identified in the source |
|---|---|
| Refrigerant circuit | Scroll compressors, suction line, EEV/liquid line, 4-way reversing valve, refrigerant service valves and refrigerant relief valves |
| Protection | Water differential pressure switch and manual-reset high-pressure switch |
| Hydronic kit | Circulating pump, insulated hydronic piping and drainage point |
| Electrical panel | Main terminal blocks, main switch, compressor contactors, controller/instrument panel and power-entry points |
5. UNICO electronic controller
Training material shown is based on software version 1.05.00, covering chiller and heat-pump configurations with up to 12 scroll compressors, including an inverter scroll plus one or two On/Off scroll compressors.
Water-temperature control
- EWT (return pipe): controls On/Off compressors.
- LWT (leaving pipe): controls the inverter plus On/Off compressors.
| Parameter | Function | Value shown |
|---|---|---|
| SC1 | Cooling temperature set-point | 7.5°C |
| SCL | Minimum cooling set-point limit | 6.0°C |
| SCH | Maximum cooling set-point limit | 20.0°C |
| SH1 | Heating temperature set-point | 44.5°C |
| SHL | Minimum heating set-point limit | 35.0°C |
| SHH | Maximum heating set-point limit | 48.0°C |
| rC1 | Cooling proportional band | 5.0 K |
| rH1 | Heating proportional band | 5.0 K |
Modbus note: The source states the SCL, SCH, SHL and SHH limits are not respected when the set-point is adjusted through Modbus. Verify remote-control strategy and site limits before commissioning remote set-point control.
Compressor timing parameters
| Code | Function | Value shown |
|---|---|---|
| CT0 | Minimum ON interval between different compressors | 30 s |
| CT1 | Minimum OFF interval between different compressors | 2 s |
| CT2 | Minimum OFF time for a single compressor | 60 s |
| CT3 | Minimum ON time for a single compressor | 180 s |
| CT4 | Minimum time between two ON cycles of the same compressor | 300 s |
| CT5 | Maximum difference in compressor running hours | 1440 min |
| CT6 | Compressor start delay from evaporator pump | 30 s |
| C50 | Maximum compressor running-hours value | 10 kh |
Evaporator-pump timing
| Code | Function | Value shown |
|---|---|---|
| P02 | Pump OFF delay after compressors stop | 60 s |
| P03 / P04 | Pump burst pulse times | Marked “Not used” |
| P21 | Pump rotation type | 2 – HOUr |
| P22 | Maximum run hours to force pump rotation | 24 h |
Starting the unit
The training material identifies four supported start methods:
- Select Turn ON from the Start menu.
- Press and hold the UP arrow for 3 seconds.
- Close the configured digital input.
- Start via Modbus/BMS.
Status and alarm menus
The Unit Status menu provides access to Input/Output, Compressor Status, Expansion Valve 1/2, Hour Counters, Refrigerant, Water, Sink/Source Regulation and Defrost Status screens. The Alarms Status menu provides Active Alarms, Reset Alarms and Alarm History.
| Compressor status | Meaning |
|---|---|
| ON / OFF | Normal compressor running / stopped state |
| Alarm | Compressor is in alarm |
| CT0, CT1, CT2, CT3, CT4, CT6 | Compressor is waiting for the corresponding timing parameter to elapse |
| Pdown | Compressor is in pump-down phase |
| DISAB | Compressor disabled by parameter |
6. Heat-pump defrost logic
Defrost demand is determined from refrigerant-circuit conditions, with suction pressure used as a key input. The controller verifies the start condition for a defined period, operates the reversing sequence, maintains a minimum defrost period and terminates defrost based on the configured stop condition or maximum time.
| Code | Defrost function | Value shown |
|---|---|---|
| d17 | Number of compressors active during defrost | 5 |
| d40 | Defrost start set-point compensation | 1 – YES |
| d09 | Defrost start pressure set-point | 4.5 barg |
| d41 | Defrost pressure set low | 3.5 barg |
| d42 | Defrost temperature set low | -5.0°C |
| d43 | Defrost pressure set high | 4.6 barg |
| d44 | Defrost temperature set high | 5.0°C |
| d10 | Defrost stop pressure set-point | 26.0 barg |
| d13 | Defrost start verification time | 180 s |
| d14 | Minimum defrost time | 30 s |
| d15 | Maximum defrost time | 7 min |
| d16 | Minimum time between two defrosts on the same refrigerant circuit | 25 min |
| d20 | Dripping / post-defrost waiting time | 30 s |
| d23 | Compressor power for circuit in defrost | 100% |
| d30 | Simultaneous defrosting mode | 2 – Ed |
| d31 | Fan speed while dripping (with relevant fan-control option) | 50% |
d30 simultaneous-defrost modes
- 0 – NO: one refrigerant system defrosts at a time.
- 1 – ES: both circuits defrost simultaneously; defrost ends when the output condition is reached on a single circuit.
- 2 – ED: both circuits defrost simultaneously; defrost ends when the output condition is reached on both circuits.
The source identifies d32, d33 and d34 as not used in this application.
Reversing-valve timing
| Code | Function | Value shown |
|---|---|---|
| rE1 | Changeover delay | 10 s |
| rEd | Changeover delay in defrost | 10 s |
7. Service quick-check sequence
| Step | Check | What to confirm |
|---|---|---|
| 1 | Unit identification | Confirm exact model/configuration, serial data, power supply, refrigerant and fitted options from the unit label. |
| 2 | Hydronic circuit | Flow available, filter clean, isolation valves open, water pressure stable and system water volume adequate. |
| 3 | Freeze protection | Confirm glycol concentration where required and verify AIS against the fluid freezing point and selection data. |
| 4 | Power supply | L1/L2/L3 within the specified tolerance, correct phase sequence, secure connections and correct heater operation. |
| 5 | Oil-heating timer | Confirm the 180-minute oil-heating delay has completed after initial power-up or an outage longer than 60 minutes. |
| 6 | Controller status | Review Active Alarms and Alarm History, then check compressor status. A CT code means the compressor is waiting on the associated timer. |
| 7 | Live values | Review Refrigerant, Water, Input/Output, Expansion Valve and Defrost Status screens before changing parameters. |
| 8 | BMS command | If remotely controlled, confirm On/Off input, emergency circuit, remote set-point source and BMS communications are not preventing operation. |
Parameter caution: Values shown above are the values displayed in the service-training material. They are a technical reference, not a direction to overwrite the configuration of every unit. Unit-specific selections, options, software revisions and factory configuration take precedence.
GENERAL AIRSTAGE Technical Reference | MultiPower Chiller & Heat Pump