11 6 RT-SVX34C-EN
Sequence of Operation
Ignition Control Module
There is a green LED located on the ignition module. Any time the Ignition module is powered, the
LED will be on to provide status of the ignition system.
• Steady OFF - no power/ internal failure
• Steady ON - no diagnostic, no call for heat
• Slow flash rate ¾ second on, ¼ second off - normal call for heat
Error Code Flashes
• One flash - Communication loss between RTRM and IGN
• Two flashes - System lockout; failed to detect or sustain flame (3 tries, lockout after 3rd try)
• Three flashes - Not used
• Four flashes - High limit switch TCO1, TCO2, or TCO3 open (auto reset)
• Five flashes - Flame sensed and gas valve not energized; or flame sensed and no call for heat
(auto reset)
The pause between groups of flashes is approximately two seconds.
High Temperature Limit Operation and Location
All of the heater limit controls are automatic reset. The high limit cutouts (TCO1) and/or (TCO3)
protect against abnormally high supply air temperature. The fan failure limit (TCO2) protects
against abnormally high heat build up due to excessive high limit (TCO1) (TCO3) cycling if the
indoor fan motor (IDM) fails. If TCO1, TCO2, or TCO3 open during a heating call, the heat will shut
down and the supply fan will be forced to run. The heat will automatically restart should the TCO
circuit re-close during an active heating call. While the TCO circuit is open, a heat fail diagnostic
will be sent from the IGN to the RTRM.
The TCO1 and TCO3 is located in the bottom right corner of the burner assemblies on both
downflow and horizontal units. TCO2 is located on the IDM partition panel; below and to the right
of the blower housing on downflow units. On horizontal units, TCO2 is located on the IDM partition
panel above the blower housing.
Electric Heat Sequence Of Operation
Constant (CV). When heat is required and the Fan selection switch is in the “AUTO” position for
constant volume applications, the RTRM energizes the Supply Fan approximately one second
before energizing the first stage electric heat contactor (AH). A 10 second minimum "off" time delay
must elapse before the first stage heater is activated. When the heating cycle is completed, the
RTRM de-energizes the Fan and the heater contactor (AH) at the same time.
The RTRM cycles the first stage of heat as required to maintain zone temperature. If the first stage
cannot satisfy the heating requirement, the RTRM energizes the second stage electric heat
contactors (BH) and (CH) providing first stage has been on for at least 10 seconds or the second
stage has been off for at least 10 seconds. (CH contactor is used on 54KW and larger heaters.)
The RTRM cycles the second stage electric heat as required to maintain the zone temperature.
Variable Air Volume (VAV). During Unoccupied heating, Morning Warmup, or Daytime
Warmup, the VHR relay will be energized for at least 6 minutes and the IGV or VFD output will go
to 100%. The heaters will stage on and off to satisfy the zone temperature setpoint.
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