YORK YCAV — LOW SUCTION PRESSURE FAULTS CAUSED BY A DEFECTIVE FEED OR DRAIN VALVE

The micro panel shows LOW SUCTION PRESSURE FAULTS CAUSED BY A DEFECTIVE FEED OR DRAIN VALVE. The manual prints the message only in this wording; there are no variants. It is one of the low suction pressure fault messages for the YCAV, and it names the feed valve or the drain valve as the suspected source of the low suction condition.

This message covers two distinct valve failures with two distinct signatures. A defective feed valve is usually accompanied by a legitimate 0% (empty) flash tank level, or a very low actual flash tank level percentage, resulting from lack of refrigerant flow; when the feed valve percentage is viewed, that valve also appears to be opening appreciably more than the feed valves of the other system(s) on the chiller. A defective drain valve behaves differently: it often appears to be open near the 100% point while starving the evaporator. The manual adds an important caveat: a low suction fault with the drain valve position near 100% and the micro panel displaying more than about 5% level in the flash tank is often caused by a defective level sensor outputting a higher than actual level, rather than by a bad drain valve.

• A defective feed valve — the lack of refrigerant flow drives the flash tank level to 0% (empty) or very low, while the valve opens appreciably more than on the other system(s) on the chiller.
• A defective drain valve that appears open near the 100% point and starves the evaporator.
• A defective level sensor outputting a higher than actual flash tank level, which mimics a bad drain valve when the drain valve sits near 100% and the displayed level is more than about 5%.
• A bad connection or corrosion on the pins in the plugs between the valve and the valve controller, or between the chiller microprocessor board and the valve controller — this causes problems with valve operation and can make the valve lose steps.

1. Operate the suspect valve in the SERVICE mode (the IOM gives the instructions for using this mode).
2. Assure the valve is operating by viewing the valve sight glass while running it from 0% to 100% and from 100% to 0%; the valve should visibly open and close smoothly.
3. On some old style valves without integral sight glasses, the only possible tests are audibly listening for valve motor operation or touching the valve to feel possible internal movement — this only assures the motor is operating and does not allow diagnosis of a valve that is sticking or uncoupled/broken from the drive motor.
4. Check any plugs in the wiring between the valve and the valve controller, as well as between the chiller microprocessor board and the valve controller, since a bad connection or corrosion on the pins causes valve problems and possible loss of steps.
5. Check the valve wiring only after a controlled shutdown, with power off.
6. If the faults occurred while the drain valve was between 90 and 100% open and the liquid line sight glass shows a solid column of liquid when the chiller is fully loaded, run the manual's test to verify the accuracy of the level sensor and whether it is causing the problem. The test requires a solid column of liquid in the sight glass; if there are bubbles, measure subcooling and assure it is between 7 and 12°F fully loaded first. Bubbles together with high subcooling mean non-condensables are likely in the system.
7. Contact Product Technical Support before changing a feed or drain valve — in almost all cases, drain and feed valves that are replaced are not defective.

• Flash tank level: a legitimate 0% (empty) or very low actual level points to the feed valve; more than about 5% displayed with the drain valve near 100% points to the level sensor instead.
• Drain valve position: a defective drain valve shows open near the 100% point; the manual cites faults occurring with the drain valve between 90 and 100% open.
• Valve test travel: run the valve from 0% to 100% and back to 0%, and finish with the valve closed at the 0% position.
• Subcooling precondition for the level sensor verification: between 7 and 12°F fully loaded.

The manual gives one closing action after the valve test: When the test is complete, be sure to close the valve to the 0% position and recycle power to the system. No other reset procedure is described for this message.