YORK YMC2 — VSD - HIGH INTERNAL AMBIENT TEMPERATURE

The panel reads VSD - HIGH INTERNAL AMBIENT TEMPERATURE. The manuals print the message in this single wording only, with no other variants. It belongs to the variable speed drive (VSD) fault messages of the YMC2 and is grouped with the cycling shutdown messages.

The variable speed drive contains two temperature sensors that monitor the unit's internal ambient temperature; the VSD logic board carries the two inputs from these sensors. The shutdown is generated when the higher of the two ambient temperatures exceeds a high limit of 158°F (70°C). The fault table summarises the condition as VSD enclosure ambient overtemperature — the air inside the drive enclosure has become too hot, so the unit is shut down.

• Internal VSD fan failure.
• VSD water pump failure — the control center manual names the same item the VSD coolant pump.
• Entering condenser water temperature higher than design.
• Condenser water flow lower than required.
• Fouled VSD heat exchanger.
• Restriction of condenser water to the VSD.

Work through the potential causes the manual lists for this shutdown, in the order given:

1. Check the internal VSD fan for failure.
2. Check the VSD water pump (called the VSD coolant pump in the control center manual) for failure.
3. Check whether the entering condenser water temperature is higher than design.
4. Check whether the condenser water flow is lower than required.
5. Check the VSD heat exchanger for fouling.
6. Check for any restriction of condenser water to the VSD.

• Trip limit: high limit of 158°F (70°C) on the higher of the two internal ambient temperature inputs.
• Recovery limit: 148°F (64°C) — below this internal temperature the unit's fan(s) and water pump(s) are de-energized and the fault can be cleared.
• Fault classification: a Cycling Fault; 3 occurrences within a 90 minute period turn it into a Safety Fault.

Clearing is tied to temperature recovery rather than a reset command: the unit's fan(s) and water pump(s) remain energized until the internal temperature drops below 148°F (64°C), after which they shall be de-energized and the fault can be cleared. As a single occurrence it is a Cycling Fault that can be cleared once the enclosure has cooled below 148°F (64°C). If 3 occur within a 90 minute period it becomes a Safety Fault, which requires user intervention and a manual clearing of the Fault Button. The manuals note this behaviour was changed at the request of Field and PTS; previously the condition required a manual reset.