YORK YCAV — Low Suction Superheat Fault

The display shows Low Suction Superheat Fault. The manual gives this wording as the only variant of the message, and it is listed in the system faults group for the unit.

This message is the Low Suction Superheat Cutout. Its purpose is to protect the compressor from liquid flood back caused by low suction superheat. When the cutout operates, the system will trip.

The safety is not active from the first moment of operation. It is ignored for the first 60 seconds of system run time, extended to 120 seconds when Soft Shutdown is Enabled, unless a restart transition has occurred. With a restart transition, the ignore timer is instead set from the current freq, with a maximum limit of 73 seconds; the timing is given under the thresholds below.

The manual also lists situations in which the fault is ignored altogether: while Soft Shutdown is in process, during ramp down while the other system is performing a soft shutdown, and for 90 seconds after ramp up starts due to ramp down/up while the other system was performing a soft shutdown.

• Startup ramp trip. After the first 30 seconds of run time — 60 seconds when Soft Shutdown is Enabled — if the suction superheat is below 2°F and the discharge superheat below 15°F while run time is still under 5 minutes, the cutout is ignored for a further 30 seconds (60 seconds with Soft Shutdown Enabled) and then ramps from 0°F to 2°F over the next 60 seconds (90 seconds with Soft Shutdown Enabled). The system trips if the suction superheat falls below this ramped cutout.
• Sustained low superheat. The system will also trip if the suction superheat stays below Suction Superheat Setpoint - 3°F (max of 5°F) for 10 minutes.

• Startup ramp cutout: ramps from 0°F to 2°F.
• Ramp entry conditions: suction superheat below 2°F, discharge superheat below 15°F, run time under 5 minutes, evaluated after the first 30 seconds (60 seconds with Soft Shutdown Enabled) of run time.
• Ignore period before the ramp: 30 seconds (60 seconds with Soft Shutdown Enabled). Ramp duration: 60 seconds (90 seconds with Soft Shutdown Enabled).
• Sustained trip threshold: Suction Superheat Setpoint - 3°F (max of 5°F), held for 10 minutes.
• Standard ignore window: first 60 seconds of system run time; 120 seconds when Soft Shutdown is Enabled.
• Restart-transition timer, capped at 73 seconds: current freq > 100 Hz — increase the timer by [(current freq - 100Hz) / 30.4 Hz/sec] + 9.5 sec; current freq <= 100 Hz — increase by [(current freq - 5Hz) / 10 Hz/sec]; in every case, increase by 60 seconds. The manual notes that 9.5 sec corresponds to the ramp from 100 Hz to 5 Hz at 10 Hz/sec.