292278-UIM-A-0108
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Unitary Products Group
Delay Taps Selection
The set of jumper pins on the control board labeled "DELAY" are used
to set the delay profiles for the furnace. These can be chosen so as to
maximize the comfort and sound levels for various regions of the coun-
try.
Tap A
is the default profile. It provides a 30-second ramp-up from zero
airflow to full capacity and a 30-second ramp-down from full capacity
back to zero airflow. Whenever there is a change in airflow mode, such
as from low heat to high heat, the motor will take 30 seconds to ramp
from one speed to the other.
Tap B
is the humid profile. This profile is best-suited for installations
where the humidity is frequently very high during cooling season, such
as in the southern part of the country. On a call for cooling, the blower
will ramp up to 50% of full capacity and will stay there for two minutes,
then will ramp up to 82% of full capacity and will stay there for five min-
utes, and then will ramp up to full capacity, where it will stay until the
wall thermostat is satisfied. In every case, it will take the motor 30 sec-
onds to ramp from one speed to another.
Tap C
is the dry profile. This profile is best suited to parts of the country
where excessive humidity is not generally a problem, where the sum-
mer months are usually dry. On a call for cooling the motor will ramp up
to full capacity and will stay there until the thermostat is satisfied. At the
end of the cooling cycle, the blower will ramp down to 50% of full capac-
ity where it will stay for 60 seconds. Then it will ramp down to zero. In
every case, it will take the motor 30 seconds to ramp from one speed to
another.
Tap D
is the normal profile, best suited for most of the country, where
neither excessive humidity nor extremely dry conditions are the norm.
On a call for cooling, the motor will ramp up to 63% of full capacity and
will stay there for 90 seconds, then will ramp up to full capacity. At the
end of the cooling cycle, the motor will ramp down to 63% of full capac-
ity and will stay there for 30 seconds, then will ramp down to zero. In
every case, it will take the motor 30 seconds to ramp from one speed to
another.
Humidistat
When a humidistat is installed in the system, the “Humidistat con-
nected?” jumper on the control board should be moved to the “YES”
position. The cooling airflow will then be reduced by 15% whenever the
humidistat indicates high humidity.
SECTION XI: NORMAL OPERATION AND
DIAGNOSTICS
NORMAL OPERATION SEQUENCE
The furnace control calculates the optimum firing rate each time the
wall thermostat R and W contacts close or open (at the beginning and
at the end of each call for heat) based on information from the thermo-
stat and past demand. UNLIKE CONVENTIONAL SYSTEMS, THE
WALL THERMOSTAT DOES NOT SIMPLY TURN THE FURNACE ON
AND OFF. THE FURNACE CONTROL CALCULATES THE DEMAND
AND MAY CONTINUE TO FIRE THE FURNACE DURING PORTIONS
OF THE THERMOSTAT "OFF" CYCLE.
When the wall thermostat R and W contacts close, indicating a call for
heat, the following sequence occurs:
1.
The inducer is energized and ramps up its speed until airflow is
proven by the pressure switch and by the pressure sensor on the
control board.
2.
The hot surface ignitor is energized.
3.
After a 17-20 second igniter heatup, the gas valve opens and the
burners light.
4.
When the control senses that flame is present, the circulating
blower starts at low speed.
5.
The furnace fires at 70% of full rate for 30-45 seconds, then drops
to the minimum (35%) firing rate.
6.
The firing rate is automatically adjusted to meet demand, increas-
ing gradually to maximum (100%) firing rate if the thermostat is not
satisfied within a defined time.
7.
When the thermostat R and W contacts open (thermostat is satis-
fied) the furnace control recalculates the demand and a new firing
rate.
a.
If demand exceeds the minimum firing rate, the burners will
continue to fire at a recalculated reduced firing rate, decreas-
ing if the thermostat remains off for a defined time.
b.
If demand does not exceed the minimum firing rate, the burn-
ers will shut off immediately.
8.
After the burners shut off, the circulating blower will continue to run
until the temperature sensor detects that the supply air tempera-
ture has dropped to the desired level, which should take from 30 to
90 seconds.
FURNACE CONTROL DIAGNOSTICS
This furnace has built-in self-diagnostic capability. If a system problem
occurs, a flashing LED shows a fault code. The LED can flash red,
green or amber to indicate various conditions. The LED is located on
the furnace control board and can be seen through the clear view port
in the lower door of the furnace. To indicate an error condition, the LED
will turn on for 1/4 second and off for 1/4 second. The pattern will be
repeated the number of times equal to the flash code. For instance, a
"six flash code" will be indicated by the LED turning on and off six times.
There will be a two second off period between each set of flashes. The
flash codes and an indication of their likely causes are listed below:
STEADY OFF -
No 24V power to board. Check the 24 volt control cir-
cuit fuse on the board. Check the circuit breaker or fuse on the 115 volt
supply power to the furnace. Check that the 24 volt transformer.
One Green Flash -
Normal Operation with no call for heat.
Two Green Flashes -
Indicator for "No error codes in memory". See
Diagnostic Fault Code Storage and Retrieval section below.
Three Green Flashes -
Indicator for "Error codes cleared from mem-
ory". See Diagnostic Fault Code Storage and Retrieval section below.
Rapid Green Flash -
Control is in "Factory Speedup" mode. This mode
is used only during factory run-testing of the furnace. To stop this mode,
cycle power to the furnace off and then back on.
One Amber Flash -
Normal operation with call for cooling.
Two Amber Flashes -
Normal operation with call for heat.
Three Amber Flashes -
Normal operation, burner is on at end of heat-
ing cycle after wall thermostat has been satisfied.
Four Amber Flashes -
Heating capacity is reduced due to restriction in
the circulating air system. Check for dirty filter or closed registers.
Five Amber Flashes -
Heating capacity is reduced due to restriction in
the combustion air or vent system. Check for blocked vent/air pipe or
clogged condensate drain. Above 4,000 feet altitude, this may also indi-
cate automatic, normal derating for altitude. See page 7 for additional
high altitude information.
Rapid Amber Flash -
Low flame sense current. Check for dirty or mis-
located flame sensor rod.
One Red Flash -
Flame is present with no power being supplied to gas
valve. This can be caused by a gas valve that is slow to close or that
leaks gas through to the burners.
Two Red Flashes -
Stuck closed pressure switch. The control confirms
that the pressure switch contacts are open at the beginning of each
cycle. This could be caused by a faulty pressure switch or by mis-wiring
of the pressure switch.
Three Red Flashes -
Stuck open pressure switch. This indicates that
the pressure switch is open when it should be closed. This could be
caused by a faulty combustion air blower, blocked vent pipe, blocked air
intake pipe, blocked condensate drain, faulty pressure switch hose or a
faulty pressure switch.
