Sterling RT - Manual (Page 15)

15
Six Stage Units: Triple duct furnace models only. Each
duct furnace is equipped with two stage heating but fi red
independently giving six stages. Each stage is 16.5% of
the units full input rate. Duct furnace one will always light
fi rst and disengage last.
Electronic Modulation Units: These units are equipped
with a electronic modulating control which provides unit
fi ring capabilities of 40 to 100% of the units full input
rate. This control is found in the gas train downstream
of the gas valve and allows main burner ignition only at
the maximum rate. A thermostat with remote setpoint
adjustment modulates the gas input.
Multi-Stage w/ Electronic Modulation Units: These
dual and triple duct furnace models are equipped with
an electronic modulating control on duct furnace one
and single or two stage heating on each successive
duct furnace. Furnace one (modulated) will fi re fi rst and
disengage last. Additional stages of heat will engage after
furnace one has fi red at maximum modulation capability
for the duration of the delay setting. The amount of
modulation and each stage size depends upon unit size
and the number of stages. See following chart.
Modulation Stage
Number Capabilities Size
of Stages (% of full input) (% of full input)
2 25 - 50 50
3 16.5 - 33 33
4 25 -50 25
6 16.5 - 33 16.5
AIR HANDLING REQUIREMENTS
AND ADJUSTMENTS
Remove wooden shipping support
from beneath blower housing of Blower Section
to prevent possible unit damage or improper unit
operation (if applicable).
Static Pressure through the unit should never exceed
2.0 inch W.C. (0.50 kPa). The standard unit is operated
at a temperature rise range of 20 to 60°F (11 to 33°C).
The high temperature rise model is operated at a
temperature rise range of 60 to 90°F (33 to 50°C).
NOTICE: It is important that the fi nal temperature
leaving the unit does not exceed 160°F (71°C). When
fi nal air throughput adjustments are being made, a
check of the discharge air temperature should be
made after unit has operated for 15 to 20 minutes.
A unit should never be allowed to cycle
on the primary limit for a prolonged period of time. It
is a safety control to prevent a fi re. If cycling on the
primary limit is noted, corrective measures should
be taken immediately. Failure to do so could result
in unit damage or a fi re.
NOTICE: At initial unit installation, unit should be
started momentarily to confi rm proper blower wheel
rotation as the unit will deliver some air with the
blower wheel running backwards.
Two basic air control systems can be used to deliver
conditioned air to the occupied space: intermittent or
constant fan operation.
Intermittent Fan Operation: The unit employs an air
control system which utilizes a fan time delay relay to
operate the fan while heating and the thermostat while
cooling. Refer to unit wiring diagram.
Constant Fan Operation: The unit can be wired to give
an air control system which constantly circulates air
through the unit and occupied space with constant fan
operation. Refer to unit wiring diagram.
NOTICE: Check blower belt tension. Proper belt
tension is important to the long life of the belt and
motor. Proper belt tension will allow the belt to be
depressed 1⁄2 inch to 3⁄4 inch.
It is important that the blower motor and the blower wheel
pulleys be in good alignment, with the motor and blower
shafts parallel.
Belt tension must be adjusted to give approximately 3/4
inch defl ection of the belt when fi nger pressure is applied
to the middle of the belt (See Figure 13). Small changes
in this tension may be necessary for optimum operation.
Belts will stretch over a period of time, requiring an
adjustment to this tension. See MAINTENANCE section
for belt and pulley adjustments.