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14 McQuay OM 751
Description of Operation
Table 8: UVC state names and numbers
OFF Mode (State 9)
Off mode is provided so that the UVC can be forced into a powered OFF condition. OFF mode
is a “stop” state for the unit ventilator; it is not a power off state. OFF mode consists of a
single UVC state: OFF [9].
When OFF mode becomes active, the UVC stops all normal heating, cooling, and ventilation
(OA damper is closed), and fan operation ends. The UVC continues to monitor space
conditions, indicate faults, and provide network communications (if connected to a network)
in the OFF mode while power is maintained to the unit.
While in OFF mode, the UVC does not maintain DA temperatures. If the space temperature
drops below EHS while in the OFF mode, the UVC is forced into the Emergency Heat mode
(see “Emergency Heat Mode (Super State)” on page 16).
The space lighting output continues to operate based upon the current occupancy mode.
Note – Special purpose unit modes such as Purge, Pressurize, and De-pressurize can force the
UVC to perform “special” functions during which the display appears to be in the OFF
mode.
Figure 7: Off state diagram
Normal UVC modes State names
State numbers
Decimal ASCII Hex
OFF OFF 9 9 57
Night purge Night Purge 8 8 56
Fan only Fan Only 10 A 65
Emergency heat
Full Heat 7 7 55
Cant Heat 13 D 68
Auto
Heat
Heat 5 5 53
Cant Heat 11 B 66
Low Limit 14 E 69
Cool
EconMech 1 1 49
Mech 2 2 50
Econ 3 3 51
DA Heat 4 4 52
Cant Cool 12 C 67
Low Limit 15 F 70
WARNING
Off mode is a “stop” state for the unit ventilator. It is not a “power
off” state. Power may still be provided to the unit.
OFF
9
UVC Mode
≠
OFF
UVC Mode
=
OF
F
Transition
point