YORK YLAA — High Discharge Pressure

The panel prints High Discharge Pressure — the manual uses no other spelling for this message, and its troubleshooting table heads the matching entry HIGH DISCHARGE PRESSURE FAULT. In the unit's Native BACnet, Modbus, and N2 communications data map the name appears as a fault/inhibit code name, reported through the Sys 1 / Sys 2 Fault Code points, where each Sys number is the system number — so the same name is reported separately for each system.

The message means the affected system has faulted on its high discharge pressure cutout. The manual describes a factory-set discharge pressure limiting function whose purpose is to keep the system from faulting on this cutout during high load or pull-down conditions; the High Discharge Pressure fault is reported when the system faults on the cutout. The manual also notes that every system has a mechanical high pressure cutout that protects against excessive high discharge pressure, whether or not the optional discharge pressure transducer is installed — and a defective discharge pressure transducer is itself one of the listed causes of this fault.

• Condenser fans not operating or operating backwards.
• Too much refrigerant — the manual's commissioning instructions warn: Do NOT overcharge the system. Otherwise High Discharge Pressure will frequently occur.
• Air in refrigerant system.
• Defective discharge pressure transducer.

1. Check the condenser fan motors and contactors, and make sure the fans blow air upward — a fan that is not operating or is running backwards is the manual's first listed cause.
2. Check the refrigerant charge: too much refrigerant is corrected by removing refrigerant. The manual says to find the system charge on the unit nameplate and add only the volume of refrigerant shown on the nameplate.
3. If air is in the refrigerant system, evacuate and recharge the system.
4. Check the discharge pressure transducer and replace it if defective; the manual's Service section gives the pressure/voltage formula for checking it.

• High Discharge Pressure Cutout — the system setpoint this fault trips on. The control center description lists it together with the anti-recycle timer (compressor start cycle time) and the anti-coincident timer (delay compressor starts).
• In the communications data map the High Discharge Pressure Cutout point is listed at AI39 / 552 / ADF 46 (x10) in PSI or BAR.