American Standard UV05 User's Manual | Page 16

American Standard Air Conditioners User's Manual - UV05.
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16

McQuay OM 751

Description of Operation

Emergency Heat Mode (Super State)

The Emergency Heat mode is provided for situations where the UVC is in a mode that does 
not normally allow heating, such as OFF, Cool, Night Purge, or Fan Only. If Emergency Heat 
mode is enabled, the UVC can automatically force itself into the Emergency Heat mode from 
OFF, Cool, Night Purge, Fan Only, Purge, Pressurize, De-pressurize, and Shutdown. 
Emergency Heat mode consists of UVC states: Full Heat [7] and Cant Heat [D].

Software model 05 does not have the primary or secondary heating devices. The UVC uses 
auxiliary heat (if field provided and field connected) when emergency heat is required.

When the Emergency Heat mode becomes active, the UVC automatically determines which 
state to make active, Full Heat [7], or Cant Heat [D], based on the transitions for each of those 
states.

Figure 10: Emergency heat state diagram

Full Heat State (State 7)

The Full Heat [7] state is the “normal” state that the UVC goes into when Emergency Heat 
mode is active. It is activated when the space temperature is lower than the EHS.

When Emergency Heat mode becomes active, the UVC goes into 100% heating until the space 
temperature raises to the EHS plus a fixed differential (5.4°F/3°C). In the Emergency Heat 
mode, the space fan is set to high speed, and the OA damper operates normally.

If the UVC automatically forces itself into the Emergency Heat mode from another mode 
(e.g., Cool, Fan Only, etc.), then the UVC returns to the appropriate unit mode once the space 
temperature rises to the EHS plus a fixed differential (5.4°F/3°C).

The UVC monitors the DAT to ensure it does not exceed DAHL. If the DAT does exceed 
DAHL, then heating is set to 0% for a minimum of 2-minutes (fixed) and until the DAT drops 
36°F (20°C) fixed differential below DAHL.

Cant Heat State (State D)

The Cant Heat [D] state is a “non-normal” state that the UVC can go into when Emergency 
Heat mode is active. An IAT or DAT sensor fault during Emergency Heat mode causes the 
UVC to make this state active.

When the Cant Heat state becomes active, the space fan remains at high speed as set during 
the Full Heat state.

The UVC will remain in the Cant Heat state until heat becomes available.

Full Heat

Cant Heat

7

D

UVC Mode 

≠ 

Emergency Heat

UVC Mode 

Emergency Heat

Transition 

point

Heat 

≠ 

Available

Heat 

Available

Emergency Heat Mode 

Super State

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