YORK YLAA — Pump Fail Make Flow

When the unit locks out, the panel shows UNIT FAULT: PUMP FAIL MAKE FLOW. In the fault/inhibit code name tables — the Native BACnet, Modbus, and N2 communications data map — the same trip is carried under the name Pump Fail Make Flow, and that is the only form the manuals print for it. The name also appears among the unit's listed data points.

Pump Fail Make Flow is a unit lockout: the control started a pump, the flow switch never closed to prove flow, so the pump was stopped and the unit was locked out. The name itself is the fault/inhibit code name carried in the Native BACnet, Modbus, and N2 communications data map, reported through the fault code points of system 1 and system 2 — the number after Sys is the system number.

The manual describes the sequence: after the 30 second stop-to-start timer has timed out, a pump is started if there is a Leaving Liquid Temperature Cut-out, or any of the compressors are running, or the daily schedule is not calling for a shutdown while the unit switch is ON and the remote stop/start input is closed. The control then waits for the flow switch to close. If the flow switch does not close within 10 seconds, the unit locks out on UNIT FAULT: PUMP FAIL MAKE FLOW and the pump is stopped. On units with two pumps, duty and standby, the running pump is stopped and the standby pump is started if the flow switch does not close within 10 seconds; if the flow switch still does not close in a further 10 seconds, the unit locks out on UNIT FAULT: PUMP FAIL MAKE FLOW and the running pump is stopped.

• The flow switch did not close within the 10 seconds allowed after a pump was started, so flow was never made.
• On units with two pumps, duty and standby: the duty pump failed to make flow and the standby pump then also failed to make flow within its further 10 seconds.
• A manual motor starter protecting one of the pumps has tripped — the manual names the pump motor starters as what to check when attempting to clear this fault.

1. Check that one of the manual motor starters protecting the pumps has not tripped; the manual gives this as the step to take in attempting to clear the fault.
2. Reset the trip by setting the unit switch to OFF, then back to ON.
3. Let the unit call the pump again and confirm the flow switch closes within 10 seconds of the pump starting; on two-pump units the control will stop the running pump and start the standby pump if flow is not made in that first 10 seconds.

• 10 seconds — the time a pump has after it is started for the flow switch to close before the pump is stopped and the unit locks out.
• A further 10 seconds — on units with two pumps, duty and standby, the time the standby pump is given before the unit locks out.
• 30 seconds — the pump stop-to-start timer that must time out before a pump is started.

The reset is the same for both forms of the trip, with one pump or with two: Setting the unit switch to OFF then back to ON resets the trip. The manual pairs this reset with the reminder to check that a manual motor starter protecting the pumps has not tripped before attempting to clear the fault. This is a lockout, so the unit stays tripped until the unit switch cycle is made.