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RT-SVX23M-EN
Sequence of Operation - Heat Pumps
Heating Operation
When the system switch is set to the “Heat” MODE, the
RTRM energizes relay (K3). When the normally open (K3)
contacts open, the switch over valves (SOV1 & 2) are de-
energized. When the zone temperature falls below the
heating setpoint controlband, the RTRM energizes the (K9)
& (K10) relay coils on the RTRM. When the (K9) relay
contacts close, the compressor contactor (CC1) coil is
energized provided the low pressure control (LPC1), high
pressure control (HPC1) and discharge line thermostat
(TDL 1) are closed. When the CC1 contacts close,
compressor (CPR1) and the outdoor fan motor (ODM)
starts provided the normally open (ODF) relay contacts are
closed.
The RTRM “Smart Recovery” function monitors the rate at
which the zone temperature is changing every 9 minutes
during the operating heating cycle. If the zone temperature
is rising at a rate greater than 6ºF per hour, no additional
heat is requested (auxiliary heat). If not, the RTRM
energizes the first stage auxiliary heat. A minimum of 10
seconds “Off” time must have elapsed between heater
cycles. If mechanical heat and first stage auxiliary heat
cannot provide the 6 F recovery rate, the RTRM energizes
second stage auxiliary heat, if applicable. The RTRM
continues to monitor the rate of change and stages the
electric heat “Off” as it determines that the mechanical
heat (compressor operation) is sufficient.
Demand Defrost
Demand defrost is a standard feature which permits
defrost whenever coil icing conditions begin to
significantly reduce unit capacity. To permit defrost, the
outdoor temperature must be below 52ºF, coil temperature
must be below 33ºF, and the delta temperature F must
exceed a RTRM calculated value. After 30 minutes of run
time under defrost permit conditions, the RTRM initiates a
defrost cycle. Upon termination of this cycle, the RTRM
monitors the outdoor temperature (ODT) and the coil
temperature (CT) and calculates the delta temperature F
(ODT - CT). This value is stored in memory and the RTRM
calculates a defrost initiate value. The RTRM continually
compares the delta temperature F to the defrost initiate
value. Once the delta tee reaches the initiate value, a
defrost cycle is initiated.
During the defrost cycle, the RTRM energizes the relay
(K3), which energizes the switch over valves (SOV1 & 2)
through the normally open K3 relay contacts. Then turns
the outdoor fan motor (ODM) “Off” by de-energizing the
(K8) relay, which de-energizes the (ODF) relay. The RTRM
energizes the auxiliary electric heat contactor (AH) and
(BH) (if applicable) if they are not operating, while
maintaining compressor (CPR1) operation.
The defrost cycle is terminated based on the RTRM
termination temperature calculation using the outdoor
temperature (ODT) + 27ºF. The defrost termination
temperature (DTT) will typically be between 37ºF and 52ºF.
Emergency Heat Operation
When the system selection switch is in the “EM HEAT”
MODE, and the zone temperature falls below the heating
setpoint controlband, the RTRM bypasses compressor
and outdoor fan operation and energizes auxiliary heat.
For gas heat, the RTRM communicates the gas heat
staging request to the gas ignition module which initiates
an ignition cycle corresponding to the requested stage.
The gas ignition module controls the spark ignition, valve
control, combustion blower and safety controls. When K1
relay contacts close, the first stage auxiliary electric heat
contactor (AH or AH and CH) is energized. If the first stage
of auxiliary electric heat can not satisfy the heating
requirement, the RTRM energizes the K2 relay coil located
on the RTRM. When the K2 relay contacts close, the second
stage auxiliary electric heat contactor (BH) is energized.
The RTRM cycles both the first and second stages of heat
“On” and “Off” as required to maintain the zone
temperature setpoint.
Verifying Proper Air Flow
Units with 5-Tap Direct Drive Indoor Fan
Much of the systems performance and reliability is closely
associated with, and dependent upon having the proper
airflow supplied both to the space that is being
conditioned and across the evaporator coil.
The indoor fan motor is factory wired to operate on speed
tap 1 in the cooling and heating mode for electric/electric
units. For gas/electric, heat pump units, the motor is
factory wired to operate on speed tap 1 during cooling. For
3 & 4 ton Gas/Electric units operating in heat mode, the
minimum setting is Tap 4.
For these units, a separate tap terminal is provided to
change speeds automatically between heating and
cooling. The motor can be rewired for different speed
settings should the application require it. Refer to the
wiring diagram that shipped in the unit and the unit fan
performance tables in the Service Facts.
WARNING
Live Electrical Components!
Failure to follow all electrical safety precautions when
exposed to live electrical components could result in
death or serious injury. When necessary to work with
live electrical components, have a qualified licensed
electrician or other individual who has been properly
trained in handling live electrical components perform
these tasks.
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