McQuay MicroTech III RAH User Manual

64 McQuay OM 920-1
Operator’s Guide
OFF Fan Retry
The unit operating state is Off Fan Retry when The Fan Retry conditions below indicate that
the unit should be shutdown and restarted after airflow is lost.
• The supply fan is controlled by a VFD
• The airflow switch (PC7) is open AND the duct static pressure is less than ½ the duct static
pressure setpoint
• There are no active faults that would shut down the unit.
Note – The unit may also be in the off operating state if any of the following are true:
• The unit is not enabled
• The unit is in the unoccupied mode and not configured for or requiring unoccupied
operation.
Start Up Operating State
When a unit is commanded to start it will always enter the Startup operating state from the Off
operating state. The unit remains in the Startup operating state for an adjustable time period
(default 180 seconds) before entering the Recirculating operating state. The parameter is
adjustable via the following path: Extended Menus/Timer Settings/Start Up.
During the Start up operating state the fans remain off, the outdoor air dampers are driven
closed, and VFD's remain at 0%. Cooling and heating are disabled.
Recirculating Operating State
Units with return air always enter the Recirculating operating state after the completion of the
Startup operating state. In the Recirculating operating state fans are started and operate while
the outdoor air dampers remain closed. This allows temperature conditions throughout the unit
and space to equalize before temperature control begins. Cooling and heating remain disabled.
The unit remains in the Recirculating operating state until the Recirculate State Timer (default
180 seconds) expires. This timer is adjustable from 0 to 30 minutes via the following path:
Extended Menus/Timer Settings/Recirculate.
Note – 100% outdoor air units do not transition through the Recirculating operating state.
Fan Only
The unit enters the Fan Only operating state after the recirculation timer expires. Units
configured for 100% outside air operation will transition directly from the Start up operating
state into the Fan Only operating state. Once entering the Fan Only state of operation the unit
will then, based on sensor inputs transition into any of the 4 remaining states of operation -
heating, cooling, economizer, or minimum discharge air heating.
Min DAT
If heating is enabled and there is no heating load (normally FanOnly operating state), the
controller activates the units heating equipment as required to prevent the discharge air
temperature from becoming too cool if the Min DAT Control Flag is set to yes via the Heating
menu (Standard Menus/Heating/Min DAT Ctrl). The unit enters the Min DAT operating state
during occupied operation when neither cooling nor heating is required based on the heat/cool
changeover function but the discharge temperature falls below a minimum discharge
temperature limit. If the discharge air temperature falls below the this minimum discharge
temperature limit by more than half the discharge heating deadband, the unit operating state
changes from Fan Only to Min DAT.
Note – On VAV or CAV discharge control units, the DAT cooling setpoint parameter in the Cooling
menu acts as the minimum discharge temperature limit. On CAV zone control units the Min
DAT Limit parameter in the Heating menu acts as the minimum discharge temperature
limit.

McQuay MicroTech III RAH Specifications

General

Brand	McQuay
Model	MicroTech III RAH
Category	Controller
Language	English