Alarm Control; Faults - McQuay MicroTech II Operation Manual

Alarm Control

The following are descriptions of the various alarms that can
occur in zone (or space comfort) control rooftop units.
Note: The cause of a manual reset alarm should be inves-
tigated and eliminated before the unit or any dis-
abled equipment in it is placed back into service.

Faults

Freeze
When a unit is equipped with a chilled water, hot water, or
steam coil, the Freeze fault occurs when the optional freez-
estat (FS1) contacts open (binary input MCB-BI7 off) as a
result of detecting an abnormally low water or steam coil
temperature while the fans are running.
When the Freeze fault occurs, the controller shuts down the
fans, closes the outdoor air dampers, opens the chilled water
and heating valves and set a 10-minute timer.
When the 10-minute timer expires, the controller checks the
freezestat input again. If the freezestat contacts are closed
(binary input MCB-BI7 on), the valves close. If the freez-
estat contacts are still open (binary input MCB-BI7 off), the
valves remain open, and the 10-minute timer resets. This
continues until the fault is manually cleared through the unit
keypad or via a network signal.
Smoke
The Smoke fault occurs when the contacts of either optional
discharge or return air smoke detector (SD1 or SD2) open
(binary input MCB-BI8 off).
When the Smoke fault occurs, the unit is immediately shut
down. The unit remains shut down until the smoke detector
is manually reset and the Smoke fault is manually cleared
through the unit keypad or via a network signal.
Note: The smoke detector can be reset by momentarily
removing power form the device. This can be
accomplishes by cycling control power (S1 switch).
Space Sensor
If the optional space temperature sensor (ZNT1) fails (ana-
log input MCB-AI1 open or short-circuited) while it is acting
as the "Control Temperature" (CtrlTemp Src= parameter is
set to "Space") and the unit has no return air sensor, the
Space Sensor fault occurs.
When the Space Sensor fault occurs, the unit is shut down. It
remains shut down until the Space Sensor fault is manually
cleared through the unit keypad or via a network signal.
Return Sensor
If the unit is equipped with a return air temperature sensor
(RAT) and it fails (analog input MCB-AI4 open or short-cir-
cuited) while it is acting as the "Control Temperature" (Ctr-
lTemp Src= parameter is set to "Return"), the Return Sensor
fault occurs.
OM 138
When the Return Sensor fault occurs, the unit is shut down.
It remains shut down until the Return Sensor fault is manu-
ally cleared through the unit keypad or via a network signal.
Disch Sensor
If the discharge air temperature sensor (DAT) fails (analog
input MCB-AI3 open or short-circuited), the Disch Sensor
fault occurs.
When the Disch Sensor fault occurs, the unit is shut down. It
remains shut down until the Disch Sensor fault is manually
cleared through the unit keypad or via a network signal.
Hi Return Tmp
If the unit is equipped with a return air temperature sensor
and the Return Air= parameter value exceeds the Hi Return
Alm= value in the Alarm Limits menu, while the unit is
operational, the Hi Return Tmp fault occurs.
When the Hi Return Tmp fault occurs, the unit is shut down.
It remains shut down until the Hi Return Tmp fault is manu-
ally cleared through the unit keypad or via a network signal.
Hi Disch Tmp
If the Disch Air= parameter value exceeds the Hi Disch
Alm= setting in the Alarm Limits menu, while the unit is
operational, the Hi Disch Tmp fault occurs.
When the Hi Disch Tmp fault occurs, the unit is shut down.
It remains shut down until the Hi Disch Tmp fault is manu-
ally cleared through the unit keypad or via a network signal.
Lo Disch Tmp
If the Disch Air= parameter value drops below the Lo Disch
Alm= setting in the Alarm Limits menu while the unit is
operational, the Lo Disch Tmp fault occurs.
When the Lo Disch Tmp fault occurs, the unit is shut down.
It remains shut down until the Lo Disch Tmp fault is manu-
ally cleared through the unit keypad or via a network signal.
Note: The Lo Disch Tmp fault is ignored when the unit
leaves the Startup operating state for a time period
defined by the Low DAT= parameter in the Timer
Settings menu and when the unit is in the Cooling
operating state.
Fan Fail
If differential pressure switch PC7 fails to detect airflow
(binary input MCB-BI6 off) within two minutes after the
unit leaves the Startup operating state or any time afterward,
while the unit is running, the Fan Fail fault occurs.
When the Fan Fail fault occurs, the unit is shut down. It
remains shut down until the Fan Fail fault is manually
cleared through the unit keypad or via a network signal.
OA Dmpr Stuck
On units equipped with a 100% outdoor air hood, the out-
door air dampers are driven fully open during the Startup
operating state before the discharge fan is started. If the OA
Damper Pos= parameter in the OA Damper menu does not
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