Heating Operation (For Gas Units) - Standard Economizer; Ignition Module Low, Medium And High; Heat; Two-Speed Indoor Fan Control - Trane Foundation GCC 090-150 Installation, Operation And Maintenance Manual

When the W2 contacts close, the second stage electric
heat contactor (BH or BH and DH) is energized, if
applicable. The thermostat cycles both the first and second
stages of heat "On" and "Off" as required to maintain the
zone temperature setpoint.
Heating Operation (for Gas Units) -
Standard Economizer
When the system switch is set to the "Heat" position and
the zone temperature falls below the heating setpoint, the
Ignition module (IGN) initiates a heat cycle.

Ignition Module Low, Medium and High

Heat

Two-stage (IGN) runs self-check (including verification that
the gas valve is de-energized). (IGN) checks the high-limit
switches (TC01 and TC01) for normally closed contacts,
the pressure switch (PS) for normally open contacts, and
the flame rollout (FR) switch for continuity. (IGN) energizes
inducer blower on high speed to check pressure switch
closure. If the pressure switch is closed, the inducer blower
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 cannot 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
and 90 second indoor blower delay off at current speed.
The (IGN) de-energizes the inducer blower at the end of
the post purge. The (IGN) de-energizes the indoor blower
at the end of the selected indoor blower delay off.
Table 8. Ignition module diagnostics
Normal, call for heat.
Slow Flash
System lockout (failure to detect or sustain
Two blinks
flame).
Pressure switch problem detected.
Three blinks
High Limit Switch protection device open.
Four blinks
Flame sensed and Gas Valve not energized
Five blinks
or flame sensed and no 'W' signal.
RT-SVX069D-EN
Table 8. Ignition module diagnostics (continued)
Flame Rollout Switch open.
Six blinks
Switch open (W1 andW2 swapped).
Seven blinks

Two-Speed Indoor Fan Control

For units equipped with two-speed indoor fan control,
standard unit operation for cooling and heating will
continue and all unit functions will operate normally, except
for the control of the indoor fan speed. All units configured
with any type of heating will heat the supply air and space
as normal utilizing full speed indoor fan by energizing the
appropriate outputs. The two-speed indoor fan unit will only
utilize two speeds during the cooling operation modes
described below.

Cooling Operation

For cooling operation, the unit will operate at Low Fan
Speed during Fan Only, Economizer Only, and the first
stage of compressor unit modes by Default. When the unit
receives a call for cooling, if the economizer is enabled, the
unit will energize the associated Low Speed output and
begin to modulate the OA Damper open above minimum
position up to 100% as necessary. By default, the supply
fan will remain at low speed for the duration of Economizer-
Only cooling. If the supply fan is on when the first stage
compressor is energized, it will remain energized or
energize at low speed for the duration of Cool 1.
When there is a call for Cool 2, the second compressor is
energized and the Supply Fan will switch to High Speed.
The unit will stage down compressors for cooling in reverse
order that they were staged and the supply fan will follow
the unit mode transitions. Once it is determined through
normal cooling control that the second compressor is no
longer necessary to meet cooling demand, the second
compressor will be staged back and the supply fan will
switch to Low Speed until the unit stages all cooling off or
receives a call for Cool 2 again. Once the Supply Fan is no
longer requested ON after a Cooling call is cleared, the
Supply Fan will remain energized at Low Speed for 60
seconds as on traditional units.
If the economizer is enabled and is being utilized as the
first stage of cooling (Y1 active), if the unit receives a Y2
request, the unit will energize the first compressor and will
switch the supply fan to high speed until the Y2 request is
cleared.

Low Pressure Cutout

The low pressure cutouts are wired in series with the high
pressure cutouts and the temperature discharge limits. If
this circuit is open before a compressor is started, the
compressor in that circuit will not be allowed to operate.
Anytime this circuit is opened, the compressor in that circuit
is turned off immediately.
Start Up
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