York Millennium Z-Series (R-410A) Packaged Rooftop Units
Comprehensive field service reference, complete 1–14 fault code diagnostic sequences, refrigerant charging metrics, electrical characteristics, and certified OEM replacement parts for York Millennium Models Z22 (25 Ton), Z23 (30 Ton), and Z24 (40 Ton).
🏷️ Model Number Nomenclature Decoder
Nameplate GuideLocate your unit model number on the data plate (located on the compressor access panel) to determine exact heating configuration, electrical voltage, and tonnage:
⚡ Complete Diagnostic Fault Code Matrix (Simplicity® Board)
Simplicity / SEC ControlsCount the flashing green/amber LED pulses on the Simplicity control board located inside the low-voltage control cabinet. Multiple safety lockouts require manual reset:
| Flash Code | System Status / Condition | Factory Diagnostic Root Cause | Field Action / OEM Part |
|---|---|---|---|
| Steady ON | Normal Operation No faults detected |
Unit is powered and running within standard factory limits. | System Standby |
| 2 Flashes | Anti-Short Cycle Delay (ASCD) Compressor delay active |
Normal 5-minute timer preventing rapid compressor recycling after power dip or thermostat call. | Wait 5 min timer expiration |
| 3 Flashes | High Pressure Lockout (Circuit 1) HP1 Switch Open (>650 PSI) |
Fouled condenser coils, failed outdoor fan motor 1, non-condensables, or overcharged R-410A. | Order Pressure Switch → |
| 4 Flashes | High Pressure Lockout (Circuit 2) HP2 Switch Open (>650 PSI) |
Fouled condenser coils, outdoor fan motor 2 failure, or restriction in liquid line filter drier. | Order Pressure Switch → |
| 5 Flashes | Low Pressure / Loss of Charge (C1) LP1 Switch Open (<50 PSI) |
Refrigerant leak, severe undercharge, failed indoor blower belt, or restricted thermal expansion valve (TXV). | Order OEM TXV Valve → |
| 6 Flashes | Low Pressure / Loss of Charge (C2) LP2 Switch Open (<50 PSI) |
Circuit 2 refrigerant undercharge, stuck liquid solenoid valve, or iced evaporator coil. | Order OEM TXV Valve → |
| 7 Flashes | Freezestat Trip (Evaporator) Suction line temp <26°F |
Extremely low indoor airflow, severely plugged 24x24x2 filters, or low return air temperature (<60°F). | Check Blower / Filters → |
| 9 Flashes | Gas Heat High Limit / Rollout Open Manual reset switch tripped |
Heat exchanger overtemperature, cracked heat exchanger tubes, flue draft restriction, or failed inducer motor. | Emergency Gas Tech → |
| 10 Flashes | Ignition Failure / Flame Loss 3 failed ignition trials |
Low gas supply pressure (<5.0 in. w.g.), dirty spark igniter/flame rod, or defective 24V gas combination valve. | Order Ignition Parts → |
| 11 Flashes | Air Proving Switch Open Blower proving failure |
Broken indoor blower belt, sheared motor drive pulley, loose blower wheel, or disconnected sensing tube. | Order OEM Blower Belt → |
| 13 Flashes | Phase Monitor Trip Reverse / loss phase |
Utility power brownout, blown main disconnect fuse, or reversed line rotation causing reverse compressor spin. | Order Phase Monitor → |
| 14 Flashes | Simplicity SEC Board Internal Fault EEPROM / Microprocessor lock |
Control transformer voltage sag (<18VAC), external electrical surge damage, or internal relay failure. | Order Replacement Board → |
⚙️ Factory OEM In-Stock Replacement Parts
● In Stock · Overnight FreightVerified OEM replacement components for York Millennium Z22, Z23, and Z24 packaged commercial units:
📊 Full Engineering Specifications (Z22, Z23, Z24 Models)
Form 036-21716 DataOfficial mechanical and electrical design parameters for York Millennium constant volume and VAV packaged units:
| Specification Parameter | Z22 (25 Ton) | Z23 (30 Ton) | Z24 (40 Ton) |
|---|---|---|---|
| Nominal Cooling Capacity | 300,000 BTU/h (25.0 Ton) | 360,000 BTU/h (30.0 Ton) | 480,000 BTU/h (40.0 Ton) |
| Refrigerant Circuits | Dual Scroll (Copeland/Danfoss) | Dual Scroll (Copeland/Danfoss) | Tandem Scroll Staged |
| Factory R-410A Charge (C1 / C2) | 15.0 lbs / 15.0 lbs | 18.5 lbs / 18.5 lbs | 24.0 lbs / 24.0 lbs |
| Electrical: 460V 3-Ph (MCA / MOP) | 58.2 A / 70 A | 69.4 A / 80 A | 91.0 A / 110 A |
| Electrical: 208/230V 3-Ph (MCA / MOP) | 124.5 A / 150 A | 148.0 A / 175 A | 192.5 A / 225 A |
| Design Airflow (CFM Range) | 7,500 – 10,000 CFM | 9,000 – 12,000 CFM | 12,000 – 16,000 CFM |
| Blower Wheel Dimensions | 18" x 18" Forward Curved | 20" x 20" Forward Curved | Dual 18" Airfoil Blower |
| Operating Weight (Cooling / Gas) | 2,850 lbs (1,293 kg) | 3,180 lbs (1,442 kg) | 3,950 lbs (1,792 kg) |
| Cabinet Dimensions (L x W x H) | 142.5" x 88.0" x 58.2" | 142.5" x 88.0" x 62.5" | 168.0" x 88.0" x 74.0" |
❄️ Field Refrigerant Charging & Subcooling Guide (R-410A)
York Millennium systems utilize thermal expansion valves (TXV); charging must strictly be performed using the Subcooling Method, never superheat alone:
Target Subcooling Parameters at Service Port:
• Design Subcooling: 10.0°F to 14.0°F (5.5°C to 7.8°C) measured at liquid line service valve.
• Design Superheat: 12.0°F to 16.0°F (6.7°C to 8.9°C) measured at compressor suction service port.
• Required Operating Test: Ensure unit runs at 100% stage 2 cooling for at least 15 minutes before reading pressure transducers.
⚠️ Never charge R-410A as a vapor. Always invert cylinder and charge liquid slowly into suction service port using a liquid-charging manifold restrictor.
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📄 Wiring Sequence & Official Technical Guide (PDF)
Cooling Sequence of Operation (Stage 1 & Stage 2)
1. Call for cooling closes G (indoor blower contactor) and Y1 (cooling stage 1).
2. Simplicity board verifies high and low pressure cutouts for closed continuity.
3. 5-minute anti-recycle delay completes; Compressor 1 and Condenser Fan 1 energize.
4. Upon call for Y2, Compressor 2 and Condenser Fan 2 stage on for 100% capacity.
Economizer & Low Ambient Operating Limits
Standard mechanical cooling operates down to 35°F (1.7°C). For sub-35°F ambient operation, verify factory low-ambient head pressure damper packages and crankcase heaters.