Safety Controls; Normal Sequence Of Operation - Trane Performance Climate Changer CSAA Series Installation, Operation And Maintenance Manual

Start-Up — Indirect Gas-Fired Heating

Safety Controls

Figure 11. Component locations
Air Proving
Switch
Ignition
Controllers
Rollout
Switch
High Limit
Switch
Manifolder Gas
Modulating Valve Inlet
• Inducer Air Proving Switch:
An air pressure switch is provided as part of the control
system to verify airflow through draft inducer by
monitoring the difference in pressure between the
draft inducer and the atmosphere. If sufficient negative
pressure is not present, indicating lack of proper air
movement through heat exchanger, the switch opens
shutting off gas supply though the ignition control
module. On units with two speed draft inducer
operation, a dual air pressure switch is used,
monitoring high and low speed pressures. The air
pressure switches have fixed settings and are not
adjustable.
• Rollout Switch (Manual Reset):
The furnace module is equipped with manual reset
rollout switch(es) in the event of burner flame rollout.
The switch will open on temperature rise and shut-off
gas supply through the ignition control module. Flame
rollout can be caused by insufficient airflow for the
burner firing rate (high gas pressure), blockage of the
vent system or in the heat exchanger. The furnace
module should not be placed back in operation until
the cause of rollout condition is identified and
corrected. The rollout switch can be reset by pressing
the button on top of the switch.
• High Limit Switch:
The furnace module is equipped with one or two fixed
temperature high limit switches mounted on the
vestibule panel that shuts off gas to the heater through
the ignition control module in the event of reduced
airflow over the heat exchanger tubes. Reduced airflow
can be caused by indoor fan failure, dirty or blocked
filters, or restriction of the air inlet or outlet to the unit.
22
Modulating
Gas Valve
Pressure Tap
Pressure Tap
On/Off Gas Valve
Component locations are approximate.
Inducer Blower
Inducer Motor
Flame
Sensor
Minimum/Maximum
Inlet Pressure =
7 in w.c./14 in w.c.
The high limit switch will automatically reset when the
air temperature drops to approximately 50°F below the
limit setpoint. Determine the cause of the reduced air
flow and correct.
• Supply Fan Air Proving Switch:
A supply fan air proving switch is provided as a part of
the gas heat control system to verify air handling unit
supply fan air flow across the heat exchanger by
monitoring the difference in pressure between the gas
heat plenum section and the atmosphere. If sufficient
positive pressure is present, the switch will be closed.
The air proving switch has fixed settings and is not
adjustable.

Normal Sequence of Operation

The gas heat module/section goes through the following
routine every time it is started. The air handler fan must be
running.
1. A call for heat is initiated by the AHU unit control
through a 0-10V analog signal.
2. The 1285 control will then go through a system check
to ensure that the high temperature limit and rollout
switches are closed, the air pressure switch is open,
and the modulating valve is positioned correctly.
3. The control will then enter the pre-purge cycle, where
the inducer will run at the programmed purge
pressure. During this cycle, the control will look for the
air pressure switch to close and open at the correct
settings.
Condensate Drain
(Typ 2)
Rollout Switch
Maximum Inlet
Pressure = 14 in w.c.
On/Off Gas Valve
Manifolder Gas
Pressure Tap
CLCH-SVX014B-EN