YORK YLAA — MP/HPCO Fault

The panel reads MP/HPCO Fault. The manual's fault table and its system-safety message list carry this name (printed in the manual's text as MP/HPCO FAULT), and the communications data map reports it through the fault code points of system 1 and system 2. Do not confuse it with the inhibit state of the same safety: while the unit is only waiting out its 30-minute timeout, the panel shows MP/HPCO INHIB (also printed MP/HP INHIBIT) instead, and that message does not mean a lockout.

MP/HPCO Fault means the MP/HPCO safety has locked the system out. The manual states the message is displayed only after 3 shutdowns in 90 min, indicating the system is locked out and will not restart. In the communications data map the name is defined as the Fault/inhibit code name in the Native BACnet, Modbus, and N2 communications data map (reported via the Sys 1 / Sys 2 Fault Code points); the numbers are the system numbers, 1 and 2.

The road to the fault: whenever the motor protector or the discharge sensor shuts down a compressor and the system, the compressor's internal contacts open for 30 min so that the motor or scroll temperatures have time to dissipate the heat and cool down. While the contacts are open — or when the HPCO is open — the inhibit message is displayed and the compressors will not be permitted to start; the microprocessor will not try to restart the compressors during this 30 min timeout. After 30 min the contacts close and the system is permitted to restart. Only a third shutdown within 90 min turns the message into the MP/HPCO Fault lockout.

• Three trips of the MP/HPCO safety inside 90 minutes — the manual states the fault message is displayed only after the third fault in 90 min, and from that point the system is locked out.
• What puts the safety into action: the manual names the motor protector or the discharge sensor shutting down a compressor and the system, which opens the compressor's internal contacts for the 30 min cool-down.

• 30 min — how long the internal compressor contacts stay open after the motor protector or discharge sensor shuts down a compressor and the system, so motor or scroll temperatures can dissipate heat; after 30 min the contacts close and the system is permitted to restart.
• 3 shutdowns in 90 min — the trip count and time window after which the panel displays MP/HPCO Fault, indicating the system is locked out and will not restart.