48VLU-E, 48VLU-F Ultra Low NOx: Product Data
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
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Controls
Operating sequence
Heating Sequence of Operation (Ultra Low NOx Single
and Three Phase Models)
On a call for heating, terminal W of the thermostat is energized, starting
the induced-draft motor for a 30 second pre-purge at normal ignition
speed. When the pressure switch senses that the induced-draft motor is
moving sufficient combustion air, the burner sequence begins. This
function is controlled by the integrated gas unit controller (IGC).
After 30 sec of pre purge is complete, the pressure switch checks for
sufficient combustion. Then, the gas valve energizes and the system
attempts to ignite with igniter being energized. The igniter energizes for
5 sec and integrated gas controller (IGC) allows system to sense flame
for 2 sec at the end of 5 sec of ignition trial. On first successful ignition,
system stays at the ignittion speed for 10 sec and ramps up to an
intermediate speed for approximately 10 sec and gradually ramps up to
the steady state speed. The system uses the same logic for 2nd and 3rd
ignition trials. In case the 4th attempt fails, the system will lock out for 1
hr. After 1 hr. lock out period, the system starts with normal operating
sequence. Once flame is established and proven successfully, indoor
(evaporator) fan motor is energized after 30 seconds. When the
thermostat is satisfied and W is de-energized, the pre-mix burner will
stop firing and the indoor (evaporator) fan motor shuts off after a 90
second time-off delay. Please note that the IGC has the capability to
automatically decrease the indoor (evaporator) fan motor "ON" delay
and increase the indoor (evaporator) fan motor "OFF" delay in the event
of high duct static and/or partially-clogged filter.
Cooling Sequence of Operation
With the room thermostat SYSTEM switch in the COOL position and
the FAN switch in the AUTO position, the cooling sequence of
operation is as follows:
1. When the room temperature rises to a point that is slightly above
the cooling control setting of the thermostat, the thermostat
completes the circuit between thermostat terminal R to terminals Y
and G.
2. The normally open contacts of energized contactor (C) close and
complete the circuit through compressor motor (COMP) to
condenser (outdoor) fan motor (OFM). Both motors start instantly.
3. The set of normally open contacts on the interface fan board (IFB)
are closed which energizes a circuit to the indoor fan motor (IFM).
NOTE:
Once the compressor has started and then stopped, it should not
be started again until 5 minutes have elapsed. The cooling cycle remains
on until the room temperature drops to a point that is slightly below the
cooling control setting of the room thermostat. At this point, the
thermostat breaks the circuit between thermostat terminal R to terminals
Y and G. These open circuits deenergize contactor coil C. The condenser
and compressor motors stop. After a 60-sec. delay, the blower motor
stops. The unit is in a standby condition, waiting for the next call for
cooling from the room thermostat.
