American Standard UV05 Cool Mode Super State, Low Limit State State E, Cant Heat State State B

Description of Operation

Note – The OAD is considered to be in “alarm” when the OAD is forced below the active minimum position in the Low Limit state. This is not an actual unit “alarm” or “fault” condition, but only a condition used for the purpose of transition arguments.

Low Limit State (State E)

The Low Limit state is a “non-normal” state the UVC can go into while Heat mode is active when the unit reaches 100% heating and still cannot meet the current DATS (see “Discharge Air Temperature Control” on page 29) required to maintain the effective heating set point (see “Space Temperature Set Points” on page 26). This is likely to occur only if the OA temperature is very cold, the OA damper minimum position is set too high, the unit ventilator is oversized for the application, or if the electric heating has failed, or is set incorrectly.

When the Low Limit state becomes active, the Low Limit PI-loop can override the OA damper position (see “Outdoor Air Damper Operation” on page 32) and adjust the OA damper toward closed as necessary to maintain the current DATS (see “Discharge Air Temperature Control” on page 29).

Cant Heat State (State B)

The Cant Heat state is a “non-normal” state the UVC can go to when Heat mode is active. An

IAT or DAT sensor fault during the Heat mode causes the UVC to make this state active.

When the Cant Heat state becomes active, no heating or ventilation takes place. The OA damper goes to the minimum position unless it is forced closed by other functions such as freezestat (T6) or morning warm-up.

Cool Mode (Super State)

When in Cool mode the UVC uses primary cooling (economizer) and secondary cooling (mechanical, DX) as needed to maintain the effective cooling set point (see “Space Temperature Set Points” on page 26). The keypad/display or network connection can be used to force the unit into the Cool mode. When the UVC is in Auto mode, it is “normal” for the UVC to “idle” in Cool mode when there is no need to switch to another mode. The Cool mode super state consists of the following UVC states: Econ Mech [1], Mech [2], Econ [3], DA Heat [4], Low Limit [F], and Cant Cool [C].

When the Cool mode super state becomes active, the UVC will automatically determine which

UVC state to make active based upon the transitions for each state.

If the space temperature drops below EHS, and the Emergency Heat function is enabled, the

UVC will be forced into the Emergency Heat mode (see “Emergency Heat Mode (Super

State)” on page 16).

18 McQuay OM 751