User`s manual

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23
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Table 7 — Altitude Compensation*
*As the height above sea level increases, there is less oxygen per
cubic foot of air. Therefore, heat input rate should be reduced at higher
altitudes.
†Orifices available through your local distributor.
Measuring Manifold Pressure — LP Gas Units
The main burner orifices on an LP gas unit are sized for the
unit rated input when the manifold pressure is 3.5 in. wg.
Proceed as follows to adjust gas input on an LP gas unit:
1. Turn off gas to unit.
2. Remove pipe plug on outlet of gas valve or on
manifold.
3. Connect manometer.
4. Turn on gas to unit and ensure gas valve operation in
second stage.
5. Remove cover screw over regulator adjustment screw
on gas valve. See Fig. 45.
6. Adjust regulator adjustment screw for a manifold
pressure reading of 3.5 in. wg (when observed under
high fire on 2-stage units). Turn adjusting screw
clockwise to increase manifold pressure, or counter-
clockwise to decrease manifold pressure.
7. Replace cover screw.
8. Turn off gas to unit.
9. Remove manometer from pressure tap.
10. Replace pipe plug on gas valve or manifold.
11. Turn on gas to unit.
12. Check for leaks.
D. Check Burner Flame
Observe the unit heating operation, and watch the burner
flames through the access door to see if they are light blue in
appearance, and that the flames are approximately the same
for each burner. See Fig. 46.
E. Airflow and Temperature Rise
The heating section of each side of the unit is designed and
approved for heating operation within the temperature rise
range stamped on the unit rating plate. Temperature rise
range is also found in Table 1.
The heating operation airflow must produce a temperature
rise that falls within the approved range.
Refer to Section III, Indoor Airflow and Airflow Adjustments
on page 26 of this section to adjust heating airflow.
F. Safety Check of Limit Control
Limit control is located on the deck next to the indoor-air
blower. The control shuts off the gas supply if the unit
overheats.
The recommended method of checking this limit control is to
gradually block off the return air after the unit has been
operating in heating for a period of at least 5 minutes. As
soon as the limit control functions, the return-air opening
should be unblocked to permit normal air circulation. By
using this method to check the limit control, it can be estab-
lished that the limit is functioning properly and the unit will
‘‘fail-safe’’ if there is a restricted circulating-air supply or
motor failure. If the limit control does not function during
this test, the cause must be determined and corrected.
G. Heating Sequence of Operation
Heating, Units Without Economizer
When the thermostat calls for heating, terminal W1 is ener-
gized. In order to prevent thermostat short-cycling, the unit
is locked into the Heating mode for at least one minute when
W1 is energized. The induced-draft motor is energized and
the burner ignition sequence begins. The indoor (evaporator)
fan motor (IFM) is energized 45 seconds after a flame is
ignited. On units equipped for two stages of heat, when addi-
tional heat is needed, W2 is energized and the high-fire sole-
noid on the main gas valve (MGV) is energized. When the
thermostat is satisfied and W1 is deenergized, the IFM stops
after a 45-second time-off delay.
Heating, Units With Economizer
When the thermostat calls for heating, terminal W1 is ener-
gized. In order to prevent thermostat short-cycling, the unit
is locked into the Heating mode for at least one minute when
ELEVATION
(FT)
125,000, 180,000,
AND 220,000 BTUH
NOMINAL INPUT
250,000 BTUH
NOMINAL
INPUT
Natural
Gas
Orifice
Size†
Liquid
Propane
Orifice
Size†
Natural
Gas
Orifice
Size†
Liquid
Propane
Orifice
Size†
0-2,000
31 41 30 38
2,000
32 42 30 39
3,000
32 42 31 40
4,000
32 42 32 41
5,000
33 43 33 42
6,000
34 43 34 43
7,000
35 44 35 43
8,000
36 44 36 44
9,000
37 45 37 44
10,000
38 46 38 45
11,000
39 47 39 45
12,000
40 47 40 46
13,000
41 48 41 47
14,000
42 48 42 47
Fig. 45 — Burner Tray Details
Fig. 46 — Monoport Burners