Problems - McQuay MicroTech II Operation Manual

indicate 50% or greater when the unit leaves the Startup
operating state, the OA Dmpr Stuck fault occurs.
When the OA Dmpr Stuck fault occurs, the unit is shut
down. The unit remains shut down until the OA Dmpr Stuck
fault is manually cleared through the unit keypad or via a
network signal.

Problems

Freeze
When a unit is equipped with a chilled water, hot water, or
steam coil, the Freeze problem occurs when the optional
freezestat (FSl) contacts open (binary input MCB-B7 off) as
a result of detecting an abnormally low water or steam coil
temperature while the fans are off.
When the Freeze problem occurs, the controller 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 while the unit remains off.
Whenever the freezestat closes (binary input MCB-BI7 on),
the Freeze problem automatically clears. This feature pro-
tects the coil(s) and allows the system to start normally when
an occupied command is received.
OAT Sensor
If the outdoor air temperature sensor (OAT) fails (analog
input MCB-AI5 open or short-circuited) and it is not acting
as the "Control Temperature" (CtrlTemp Src= parameter is
not set to "OAT"), the OAT Sensor problem occurs.
When the OAT Sensor problem occurs, the unit continues to
operate with the following modifications:
1. Discharge temperature set point reset based on outdoor
air is unavailable.
2. Compressor low ambient lockout is disabled.
3. High ambient heating lockout is disabled.
4. Purge operation is disabled. Space Sensor
When the alarm condition is no longer present, the OAT Sen-
sor problem automatically clears.
Space Sensor
If the optional space temperature sensor ZNT1 fails (analog
input MCB-AI1 open or short-circuited) on a unit equipped
with a return air temperature sensor, the Space Sensor prob-
lem occurs as long as the Space Sensor= parameter in the
Unit Configuration menu is set to "Yes." If this parameter is
set to "No" the Space Sensor problem indication is disabled.
When the Space Sensor problem occurs, the unit continues
to operate with the following modifications:
1. Discharge temperature set point reset based on space
temperature is unavailable.
2. Purge operation is disabled.
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3. If the space temperature input is acting as the "Control
Temperature" (CtrlTemp Src= parameter is set to
"Space"), the controller automatically changes the Ctr-
lTemp Src= parameter to "Return".
When the Space Sensor problem occurs during an unoccu-
pied time period, the unit starts and runs continuously in the
UnocHtg operating state, using the return air temperature
sensor as the "Control Temperature" if all of the following
conditions are true:
1. The unit is equipped with a return air temperature sen-
sor.
2. The OA Temp= parameter value is below 40 °F.
3. The UnoccHtg Spt= parameter in the Zone Heating
menu is set higher than 0°F.
When the alarm condition is no longer present, the Space
Sensor problem automatically clears and normal unit opera-
tion resumes.
Return Sensor
If the return air temperature sensor (RAT) fails (analog input
MCB-AI4 open or short-circuited) while it is not acting as
the "Control Temperature" (CtrlTemp Src= parameter is not
set to "Return"), the Return Sensor problem occurs.
When the Return Sensor problem occurs, the unit continues
to operate with the following modifications:
1. Discharge temperature set point reset based on return
temperature is unavailable.
2. The Hi Return Tmp fault is disabled.
When the alarm condition is no longer present, the Return
Sensor problem automatically clears.
Ent Fan Sensor
If the unit is equipped with an entering fan air temperature
sensor (EFT) and it fails (analog input MCB-AI6 open or
short-circuited), the Ent Fan Sensor problem occurs as long
as the EFT Sensor= parameter in the Unit Configuration
menu is set to "Yes." If this parameter is set to "No" the Ent
Fan Sensor problem indication is disabled.
When the Ent Fan Sensor problem occurs, the unit continues
to operate with the following modifications.
1. The Low Airflow problem is disabled.
2. The function on gas or electric heat units that limits the
Eff Htg Spt= parameter in the Discharge Heating menu
based the maximum heat rise for the heat exchanger on
units equipped with gas or electric heat is disabled.
Refer to "Heating: Multistage" on page 78 (electric heat
units) or "Gas Heat" on page 82 (gas heat units).
When the alarm condition is no longer present, the Ent Fan
Sensor problem automatically clears.
Note: Note that the EFT sensor is only provided with units
that have gas or electric heat.
Heat Fail
If a unit is equipped with a gas furnace (one-stage or modu-
lating) and the burner flame safeguard (FSG) control enters
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