Sequence of Operation
50 RT-SVX25Q-EN
types, the Supply Fan will be controlled at maximum fan
speed during active heating operation as during Occupied
periods.
Electric Heat Control
The RTRM provides two heating outputs for 1st and 2nd
stages that will be controlled with at least a 10 seconds
delay between each stage. When the fan selection switch
is in the “AUTO” mode, the fan will start approximately 1
second before the 1st heater stage is activated. The fan
and heater will cycle off after the heating setpoint has been
satisfied. Once the Zone Heating requirements have been
satisfied, the fan and heat outputs will be controlled off.
Constant Volume or Variable Air
Volume Applications (SZVAV or
Traditional)
Clogged Filter Option
The unit mounted clogged filter switch monitors the
pressure differential across the return air filters. It is
mounted in the indoor section and is connected to the
RTOM. The clogged filter switch is normally open and will
automatically close when the pressure differential across
the filters falls below the clogged filter setpoint. The RTOM
will generate a SERVICE diagnostic that will be sent to the
zone sensor or remote panel when the clogged filter switch
has been closed for at least 2 minutes during supply fan
operation. The system will continue to operate regardless
of the status of the clogged filter switch.
Ventilation Override
Note: Applying 24 volts to one of the three Ventilation
Override Inputs manually activates ventilation
override. One input is provided to request the
Pressurize Mode, the second input the Purge Mode,
and the third input the Exhaust Mode.
When the Pressurize Mode is selected, ac
tivating
Ventilation Override will cause the supply fan to run, the
economizer to open to 100%, the exhaust fan to turn
(remain) off, or the VFD to run at full speed (SZ VAV and
Traditional VAV), and the VAV boxes to fully open.
When Purge is selected, activating Ventilation Override
wi
ll caus
e the supply fan to run, the economizer to open to
100%, the exhaust fan to run, or the VFD to run at full speed
(SZ VAV or Traditional VAV), and the VAV boxes to fully
open.
When Exhaust is selected, activating Ventilation Override
wi
ll cause the supply fan to turn off, the economizer to
close to 0%, the exhaust fan to run (exhaust damper at
100% if configured for Statitrac), or the VFD to stop, and
the VAV boxes to operate normally.
If more than one mode is requested at the same time, the
Pr
essurize request will
have priority followed by Purge.
When any Ventilation Override Mode is active, all heating
and cooling is turned off. For the case where the unit is
required to turn off, the Emergency Stop input is used. The
ICS can also initiate any ventilation override mode.
Table 17 lists the sequence of events within the system
for
each venti
lation mode. Refer to the unit wiring diagram for
contact switching and wiring.
Note: Fr
esh air tracking will not work with
VOM.
Table 17. Ventilation override sequence
Mode and Priority
Affected
Function Pressurize Purge Exhaust
(a)
(a) Exhaust mode 3 is not available with the tracking power exhaust
option.
1 2 3
Heat/Cool off off off
VFD full speed full speed full speed
Supply Fan on on off
Exhaust Fan off on
(b)
(b) For units configured with the Statitrac option, the Exhaust Damper
will open during Ventilation Override modes that request the ex-
haust fan to operate.
on
Economizer open open closed
VAV Boxes forced open forced open
normal
operation
Emergency Stop
When this binary input is opened, all outputs are
immediately turned off and the system will not be allowed
to restart until the binary input is closed for approximately
5 seconds minimum. The shutdown is communicated to
Tracer™ if applicable and the Heat and Cool LED outputs
(RTRM J6-7 and J6-8) will blink at a nominal rate of 1 blink
per second.
Phase Monitor
The Phase Monitor is a 3 phase line monitor module that
protects against phase loss, phase reversal and phase
unbalance. It is intended to protect compressors from
reverse rotation. It has an operating input voltage range of
190-600 VAC, and LED indicators for ON and FAULT. There
are no field adjustments and the module will automatically
reset from a fault condition.
Low Pressure Control
This input incorporates the low pressure cutout of each
refrigeration circuit and can be activated by opening a field
supplied contact.
If this circuit is open before a compressor(s) is started,
neither compressor
in that circuit will
be allowed to
operate.
Anytime this circuit is opened for 5 continuous seconds,
the compressor(s) in that c
ircuit are turned off
immediately. The compressor(s) will not be allowed to
restart for a minimum of 3 minutes.
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