Sequence of Operation
RT-SVX26R-EN
43
actuator (ECA) to open the economizer damper. The RTRM
tries to cool the zone utilizing the economizer to slightly
below the zone temperature setpoint. If the mixed air
sensor (MAS) senses that the mixed air temperature is
below 53°F, the damper modulates toward the closed
position. If the zone temperature continues to rise above
the zone temperature setpoint controlband and the
economizer damper is fully open, the RTRM energizes the
first stage compressor contactor (CC1). If the zone
temperature continues to rise above the zone temperature
setpoint controlband and the economizer damper is fully
open, the RTRM energizes the second stage compressor
contactor (CC2). The ECA continues to modulate the
economizer damper open/closed to keep the mixed air
temperature that is calculated by the RTRM. If
economizing is not possible, the ECA drives the damper to
the minimum position setpoint when the indoor fan relay
(F) is energized and allows mechanical cooling operation.
When the unit is equipped with the optional fan failure
switch (FFS), wired to the RTOM, the RTRM will stop all
cooling functions and produce an analog output if the fan
failure switch (FFS) does not open within 40 seconds after
a request for fan operation. When the system is connected
to a remote panel, the “SERVICE” LED will flash when this
failure occurs.
Economizer Set-Up
Adjusting the minimum position potentiometer located on
the unit economizer actuator (ECA) sets the required
amount of ventilation air.
Two of the three methods for determining the suitability of
the outside air can be selected utilizing the enthalpy
potentiometer on the ECA, as described below:
1. Ambient Temperature-Controlling the economizing
cycle by sensing the outside air dry bulb temperature.
lists the selectable dry bulb values by
potentiometer setting.
2. Reference Enthalpy-Controlling the economizer cycle
by sensing the outdoor air humidity. Table 10 lists the
selectable enthalpy values by potentiometer setting. If
the outside air enthalpy value is less than the selected
value, the economizer is allowed to operate.
3. Comparative Enthalpy-By utilizing a humidity sensor
and a temperature sensor in both the return air stream
and the outdoor air stream, the unit control processor
(RTRM) will be able to establish which conditions are
best suited for maintaining the zone temperature, i.e.
indoor conditions or outdoor conditions.
The potentiometer located on the ECA is non-functional
when both the temperature and humidity sensors are
installed.
ReliaTel Control Heating Operation for Gas
Units
When the system switch is set to the “Heat” position and
the zone temperature falls below the heating setpoint
controlband, a heat cycle is initiated when the RTRM
communicates ignition information to the Ignition module
(IGN).
Modulating Gas Heat 2.5:1
Turndown, in a modulating heat unit, when a call for heat
is received, the burner will light at full fire (100%). After the
burner is lit, the unit controls will monitor the discharge air
temperature and modulate the input rate down to match
the load.
Ignition Control Module
Two-Stage (IGN) runs self-check (including verification
that the gas valve is de-energized). IGN checks the high-
limit switches (TC01 and TC02) for normally closed
contacts. With power supplied to the ignition module
(IGN), the hot surface ignition probe (IP) is Preheated. The
gas valve (GV) is energized for a few seconds for trial for
ignition, to ignite the burner. Once the burner is ignited,
the hot surface ignition probe (IP) is de-energized by the
ignition module (IGN) and functions as the flame sensing
device. If the burner fails to ignite, the ignition module will
attempt two retries before locking out. The green LED will
indicate a lockout by two fast flashes. An ignition lockout
can be reset by:
1. Opening for 3 seconds and closing the main power
disconnect switch.
2. By 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
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
Table 17. Potentiometer settings
Potentiometer
Setting
Dry Bulb
Enthalpy
A
27 Btu/lb (63 kJ/kg)
73°F(22.8°C)
B
25 Btu/lb (58 kJ/kg)
70°F (21.1°C)
C
(a)
(a) Factory setting
23 Btu/lb (53 kJ/kg)
67°F (19.4°C)
D
22 Btu/lb (51 kJ/kg)
63°F (17.2°C)
E
19 Btu/lb (44 kJ/kg)
55°F (12.8°C)
