Control Timer Settings - McQuay MicroTech II Operation Manual

Control Timer Settings

Table 26: Programmable Parameters
Keypad/Display ID
Menu Name Item Name
Service= 0 min
Recirculate= 3 min
Low DAT= 3 min
Max MWU= 90 min
Timer Settings
Bypass= 120 min
Start Init= 120 min
Min Exh On= 120 sec
Min Exh Off= 120 sec
Several MicroTech II internal control timers can be adjusted
via the keypad/display Timer Settings menu. The following
sections describe these timers.
Service
Many of the internal control timers can be temporarily sped
up by using the Fast Service Timer. When set to a time value,
the Fast Service Timer begins counting down. While this
parameter is counting down the following normal unit timers
are set to 20 seconds:
Startup Initialization Timer
l
Post Heat Timer
l
Cooling Interstage Timer
l
Heating Interstage Timer
l
These timers return to their normal settings if the Fast Ser-
vice Timer is manually set to 0 or when it counts down to 0.
Caution: This fast timers feature is meant to be used only
by a knowledgeable service technician to facili-
tate testing the unit.
Recirculate
The Recirculate State Timer defines the duration of the
Recirc operating state applicable on units with return air
(100% OA units have no Recirc operating state). Whenever
a unit with return air is started or restarted, it always transi-
tions through a "start sequence" which includes the Startup,
followed by the Recirc operating state. During the Recirc
operating state, the unit fans run while the outdoor air damp-
ers remain closed. Heating and cooling operation are dis-
abled during the Recirc operating state to allow the "system"
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air temperature conditions to equalize before temperature
control begins. Once in the Recirc operating state, the unit
remains there until the Recirculate State Timer expires.
Low DAT
Parameter Name
The Low Discharge Temperature Ignore Timer sets the dura-
Fast Service Timer
tion of a time period after unit start up during which the Lo
Recirculate State
Disch Tmp fault is ignored. This may be particularly impor-
Timer
tant in colder climates when a unit has been off for a signifi-
Low Discharge Tem-
cant time period during which the unit, including the
perature Ignore Timer
discharge air temperature sensor, has become very cold. This
Maximum Morning
Warm-up Timer
time period allows the unit to run long enough to warm the
Bypass Time Incre-
discharge sensor above the alarm limit, preventing nuisance
ment
unit alarm shutdown. For detailed information regarding the
Startup Initialization
Lo Disch Tmp fault refer to "Alarm Control" on page 91.
Timer
Minimum Exhaust
Max MWU
Fan On Timer
Minimum Exhaust
The Maximum Morning Warm-up Timer sets a maximum
Fan Off Timer
duration for the MWU operating state applicable on units
with return air (100% OA units have no MWU operating
state). Whenever a unit with return air leaves the Recirc
operating state, it enters the MWU operating state if the Ctrl
Temp= parameter value is cold. The unit remains in the
MWU operating state until either the Ctrl Temp= parameter
value warms up or until the Maximum Morning Warm-up
Timer expires. For detailed information regarding MWU
operation, refer to "Heating: Multistage" on page 78, or
"Heating: Modulating" on page 80, as applicable.
Bypass
The Bypass Time Increment sets the time period for which
the unit operates each time the tenant override button on the
optional space temperature sensor is pressed or the Occ
Mode= parameter is set to "Bypass." The Bypass Time=
parameter in the Occupancy menu is set or reset to this value
when the tenant override button is pressed or the Occ Mode=
parameter is set to "Bypass." The unit then operates until the
Bypass Timer= parameter counts down to 0. For detailed
information regarding bypass operation, refer to "Bypass
Time (Tenant Override)" on page 48.
Start Init
The Startup Initialization Timer defines the duration of the
Startup operating state. When a unit is started or restarted, it
always transitions through a "start sequence" that begins
with the Startup operating state. During the Startup operating
state, the unit fans remain off and heating and cooling are
disabled. On units equipped with return air, the outdoor air
damper actuator is driven closed. On units equipped with
100% outdoor air hoods, the outdoor air dampers are driven
fully open. Return fan inlet vane actuators (if present) are
driven to a 17% minimum startup position. Refer to "Operat-
ing States and Sequences" on page 61.
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