18
RT-SVF25C-EN
Sequence of Operation
starts a 20-second pre-purge (15 seconds on high speed
followed by 5 seconds on low speed). If the pressure
switch (PS) is still open, the inducer blower will continue to
be energized on high speed until pressure switch closure.
After pre-purge completes, the (IGN) energizes the first
stage of the gas valve, initiates spark for 2 seconds
minimum, 7 seconds maximum (ignition trial) and detects
flame and de-energizes spark. From this point, a fixed 45
second indoor blower delay on timing starts. After the
indoor blower delay on is completed, the (IGN) energizes
the indoor blower. The (IGN) enters a normal operating
loop where all inputs are continuously monitored. If the
first stage of gas heat can not satisfy the heating
requirement, the thermostat closes W2. The (IGN)
energizes the second stage of the gas valve and the second
stage of inducer blower. When the zone thermostat is
satisfied, the (IGN) de-energizes the gas valve. The (IGN)
senses loss of flame.The (IGN) initiates a 5 second inducer
blower post purge. The (RTRM) initiates a second indoor
blower delay off.
If the burner fails to ignite, the ignition module will attempt
two retries before locking out.The green LED will indicate
a lock out by two fast flashes. An ignition lockout can be
reset by;
1.
Opening for 3 seconds and closing the main power
disconnect switch.
2. Switching the “Mode” switch on the zone sensor to
“OFF” and then to the desired position.
3. Allowing the ignition control module to reset
automatically after one hour. Refer to the “Ignition
Control Module Diagnostics” section for the LED
diagnostic definitions.
When the fan selection switch is set to the “Auto” position,
the RTRM energizes the indoor fan relay (F) coil
approximately 30 second after initiating the heating cycle
to start the indoor fan motor (IDM).
Drain Pan Condensate Overflow Switch
(Optional)
This input incorporates the Condensate Overflow Switch
(COF) mounted on the drain pan and the ReliaTel Options
Module (RTOM). When the condensate level reaches the
trip point for 6 continuous seconds, the RTOM will shut
down all unit function until the overflow condition has
cleared. The unit will return to normal operation after 6
continuous seconds with the COF in a non-tripped
condition. If the condensate level causes the unit to
shutdown more than 2 times in a 3 day period, the unit will
be locked-out of operation. A manual reset of the
diagnostic system through the zone sensor or Building
Automation System (BAS) will be required. Cycling unit
power will also clear the fault.
Electromechanical Controls
These units are offered with two control options,
electromechanical and ReliaTel controls. The ReliaTel
controls is a microelectronic control feature, which
provides operating functions that are significantly
different than conventional electromechanical units.
Electromechanical Control Cooling
without an Economizer
When the thermostat switch is set to the “Cool” position
and the zone temperature rises above the cooling setpoint,
the thermostat Y 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) start. If the first stage of cooling can not
satisfy the cooling requirement, the thermostat closesY2.
The compressor contactor (CC2) coil is energized provided
the low pressure control (LPC2), high pressure control
(HPC2) and discharge line thermostat (TDL 2) are closed.
When the (CC2) contacts close, compressor (CPR2) starts.
Electromechanical Control Evaporator Fan
Operation (for Gas Units)
When the thermostat fan selection switch is set to the
“Auto” position, the Ignition Module (IGN) energizes the
indoor fan relay (F) approximately 1 second after
energizing the compressor contactor coil (CC1) in the
cooling mode. In the heating mode, the Ignition Module
(IGN) energizes the indoor fan relay (F) coil approximately
45 second after gas ignition. Closing indoor fan relay (F)
coil starts the indoor fan motor (IDM). The (IGN) de-
energizes the fan relay (F) approximately 80 seconds after
the cooling requirement has been satisfied to enhance unit
efficiency.
When the heating cycle is terminated, the indoor fan relay
(F) coil is de-energized approximately 90 seconds after the
heating requirement.
Table 21.
Ignition module diagnostics
Steady light
Module is powered up, but no active call for
heat.
Blinking at
continuous
steady rate
Active call for heat.
One blink
Loss of communication.
Two blinks
System lockout (failure to ignite, no spark, low/
no gas pressure, etc.)
Three blinks
Pressure switch (no vent air flow, bad CBM,
closed at initial call for heat). Auto reset.
Four blinks
High limit (excessive heat in combustion
chamber, low airflow). Auto reset.
Five blinks
Flame sensed and gas valve not energized or
flame sensed and no call for heat.
Six blinks
Flame rollout (CBM failure, incorrect gas
pressure, incorrect primary air). Requires
manual reset of the switch.
Seven blinks
ReliaTel module will communicate a heat fail
diagnostic back to the RTRM.
