YORK YCAV — LOW SUCTION PRESSURE FAULTS CAUSED BY AN INCORRECT LEVEL SENSOR OUTPUT

The micro panel shows LOW SUCTION PRESSURE FAULTS CAUSED BY AN INCORRECT LEVEL SENSOR OUTPUT. The manual prints the message in this single form.

This message reports a low suction pressure fault brought about by a flash tank level sensor that reads higher than the level actually in the tank. A sensor of this kind carries a positive offset error of more than 10% on the micro panel display percentage: for example, the tank is actually at 35% while the display indicates 45%. When the displayed value sits more than 10% above the real level, the flash tank can run out of refrigerant at low discharge pressures or while the compressor accelerates. Once the tank runs dry, the drain valve can no longer control superheat and suction pressure falls. In some cases the system merely enters suction limiting and does not accelerate in speed; in others it trips on low suction pressure.

• A level sensor whose displayed percentage carries a positive offset error of more than 10%; a problem sensor normally reads high compared with the actual tank level.
• Corroded or loose pins in the plugs joining the level sensor to the chiller control (microprocessor) board, which make the displayed level intermittent or erratic.

1. Review the history buffer. When the flash tank has run empty and the evaporator is starved, the drain valve often sits near 100% (typically over 90%) when the fault occurs, and the displayed flash tank level typically still reads 5% or more even though the tank may be empty.
2. Operate the drain and feed valves in SERVICE mode to rule out a faulty valve, wiring, or controller.
3. Run the system under enough load to open the economizer valve while a solid column of liquid shows in the liquid line sight glass, and bring the level to or near the middle of the flash tank sight glass (bottom of glass = 32%, middle = 35%, top = 38%).
4. To reach that level faster, the FEED VALVE LEVEL SETPOINT (SERVICE 2878 ENTER) may be raised temporarily by keying in 45.0. DO NOT change any other programmed point under the password protected displays.
5. Compare the display with the glass. The display must indicate between 25% and 45% and sit less than 10% above the percentage the sight glass actually shows. If the reading falls outside this window and low suction pressure faults keep occurring, the level sensor should be replaced.
6. To expose an intermittent sensor, lightly tap the level sensor's electronics enclosure using a screwdriver handle and watch whether the display changes significantly.
7. Inspect the plugs joining the level sensor to the chiller control (microprocessor) board: a corroded or loose pin connection makes the displayed level intermittent or erratic.
8. Leave the sensor in place unless its displayed level is numerically more than 10% above what the sight glass actually shows; if the error is smaller, contact factory technical support before changing it.

• FEED VALVE LEVEL SETPOINT — reached at SERVICE 2878 ENTER; may be raised temporarily to 45.0 to speed up the sensor check.
• Flash tank sight glass reference points: bottom of glass = 32%, middle = 35%, top = 38%.
• Acceptable display window: between 25% and 45%, and less than 10% above the level the sight glass actually shows.
• Offset threshold: a positive error of more than 10% on the micro panel display percentage marks a problem sensor.
• History buffer markers of an emptied flash tank: drain valve near 100% (typically over 90%) at the fault; displayed level of 5% or higher.