Sterling RT - Manual (Page 16)

16
Figure 13 - Belt Tension Guide
These units are set at the factory for the RPM required to
meet the air volume (CFM) and external static pressure
ordered. If the estimated external static is incorrect, or
changes were made to the duct system, the blower RPM
may need to be changed.
Both the Standard and High CFM Blowers use motors
which are equipped with adjustable pitch pulleys. After
removing belt(s), loosen the pulley set screw and remove
the key, turn adjustable half of a pulley clockwise to
increase RPM, or counter-clockwise to decrease RPM.
Insert key, tighten set screw and replace belt(s). Adjust
belt tension to give 1⁄2 inch to 3⁄4 inch belt play when
depressed.
Blower motor full load amps should
never be exceeded. Improper unit operation or motor
failure could result.
After changing blower RPM, confi rm blower motor full load
amps have not been exceeded. See motor data plate for
maximum full load amps.
LIGHTING
(Refer to Outdoor Duct Furnace Manual for all heating
functions - general comments are as follows.) Purge the
gas line to the unit of air before attempting to light the
pilot. Check for gas leaks.
Never use an open fl ame to detect
gas leaks. Explosive conditions may exist which
could result in personal injury or death.
This unit is equipped with an intermittent ignition system.
A lighting instruction is attached to the unit. To set the
intermittent ignition system into operation proceed as
follows:
1. Turn on the gas valve(s) main manual valve.
2. Turn on electrical power. The unit is now under
thermostat control.
3. Set thermostat to highest level. This will initiate the
sequence of operation detailed in the Gas Control
System section. Check main burners for operation.
4. Set thermostat to lowest level. This will interrupt power
to the ignition control and shut off gas. Confi rm pilot
and main burners have been extinguished.
5. Set the thermostat to the desired setting.
For complete unit shutdown, proceed as follows:
1. Turn off the gas valve(s) main manual valve.
2. Set thermostat to lowest setting.
3. Shut off all electric power.
GAS INPUT ADJUSTMENT
When shipped from the factory, all units are equipped
for the average heat content of the gas which is stamped
on the unit rating plate.
Since the heat content of gas varies by
locality, the input must be checked after installation
of the unit. If the unit is overfi red it will shorten the
life of the heat exchanger. Never exceed the input on
the rating plate.
For an accurate input rate measurement the following
meter method should be used to determine unit input rate.
If the meter method is not possible, a manifold pressure
check should be made.
Meter Method of Checking Input Rate
1. Obtain the heating value of the gas from the local
utility or gas dealer. This should be in units of Btu/ft 3
(MJ/m 3 ).
2. Determine the gas fl ow rate as shown in the following
example. EXAMPLE: Assume this unit has a input rate
of 250,000 Btu/hr (73.2 kW) and the heating value of
the gas is 1000 Btu/ft
3 (37.3 MJ/m 3 ).
Gas 250,000 Btu/hr (73.2 kW)
Flow =
Rate
1000 Btu/ft 3 (37.3 MJ/m 3 ) x 60 min/hr
= 4.17 ft 3 /min (1.974 L/s)
3. Before determining the gas fl ow rate to the unit, all
other gas appliances connected to the same meter
must be turned off.
4. Fire unit according to instructions.
5. After approximately 15 minutes of unit operation,
determine volume of gas used in fi ve minutes of unit
operation. For the Example above the unit should
use 4.17 ft
3 /min x 5 min or 20.8 ft 3 (1.97 L/s x 5 min x
60 s/min = 591L) of gas. Minor input adjustments
can be made by removing pressure regulator cap
and turning regulator clockwise to increase input or
counter clockwise to decrease input. Any appreciable
adjustment in input rate should be made by reorifi cing.
1/2" TO 3/4"