35
g. Replace orifice with correct size if required by Table
12 or 13. Use only factory--supplied orifices. See
EXAMPLE 2.
EXAMPLE 2: (0--2000 ft. altitude)
For 22,000 Btuh per burner application use Table 12.
Heating value = 1000 Btuh/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 43*
Manifold pressure: 3.7--in. wc
*Furnace is shipped with No. 43 orifices. In this example all main
burner orifices are the correct size and do not need to be changed
to obtain proper input rate.
3. Adjust manifold pressure to obtain correct input rate.
a. Turn gas valve ON/OFF switch to OFF.
b. Remove manifold pressure tap plug from gas valve.
(See Fig. 47.)
c. Connect a water column manometer or similar device
to manifold pressure tap.
d. Turn gas valve ON/OFF switch to ON.
e. Manually close blower door switch.
f. Set thermostat to call for heat.
g. Jumper R and W thermostat connections on furnace
control board to start furnace.
h. Remove regulator seal cap and turn regulator adjusting
screw counterclockwise (out) to decrease input rate of
clockwise (in) to increase input rate.
i. Install regulator seal cap.
j. Leave manometer or similar device connected and
proceed to Step 4.
NOTE
: DO NOT set manifold pressure less than 3.2--in wc or
more than 3.8--in. wc for natural gas at sea level. If manifold
pressure is outside this range, change main burner orifices or refer
Table 12 or 13.
NOTE
: If orifice hole appears damaged or it is suspected to have
been redrilled, check orifice hole with a numbered drill bit of
correct size. Never redrill an orifice. A burr--free and squarely
aligned orifice hole is essential for proper flame characteristics.
4. Verify natural gas input rate by clocking meter.
NOTE
: Gas valve regulator adjustment cap must be in place for
proper input to be clocked.
a. Turn off all other gas appliances and pilots served by
the meter.
b. Run furnace for 3 minutes in heating operation.
c. Measure time (in sec) for gas meter to complete 1 re-
volution and note reading. The 2 or 5 cubic feet dial
provides a more accurate measurement of gas flow.
d. Refer to Table 10 for cubic ft. of gas per hr.
e. Multiply gas rate (cu ft./hr) by heating value (Btu/cu
ft.) to obtain input.
If clocked rate does not match required input from Step 1,
increase manifold pressure to increase input or decrease manifold
pressure to decrease input. Repeat steps b through e until correct
input is achieved. Reinstall regulator seal cap on gas valve.
5. Set temperature rise. The furnace must operate within the
temperature rise ranges specified on the furnace rating
plate. Do not exceed temperature rise range specified on
unit rating plate. Determine the temperature rise as fol-
lows:
NOTE
: Blower access door must be installed when taking
temperature rise reading. Leaving blower access door off will
result in incorrect temperature measurements.
a. Place thermometers in return and supply ducts as close
to furnace as possible. Be sure thermometers do not
see radiant heat from heat exchangers. Radiant heat
affects temperature rise readings. This practice is par-
ticularly important with straight--run ducts.
b. When thermometer readings stabilize, subtract return--
air temperature from supply--air temperature to determ-
ine air temperature rise.
NOTE
:
Blower access door must be installed for proper
temperature rise measurement.
NOTE
: If the temperature rise is outside this range, first check:
1.) Gas input for heating operation.
2.) Derate for altitude if applicable.
3.) Return and supply ducts for excessive restrictions causing
static pressures greater than 0.50--in. wc.
4.) Dirty filter.
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or death.
Disconnect 115--v electrical power before changing speed
tap.
!
WARNING
c. Adjust air temperature rise by adjusting blower speed.
Increase blower speed to reduce temperature rise.
Decrease blower speed to increase temperature rise.
d. Turn thermostat down below room temperature and
remove blower access door.
e. To change motor speed selection for heating, remove
blower motor lead from control HEAT terminal (See
Fig. 25.) Select desired blower motor speed lead from
one of the other terminals and relocate it to the HEAT
terminal (See Table 9 for lead color identification).
Reconnect original lead to SPARE terminal.
TABLE 9—SPEED SELECTION
COLOR
SPEED
AS SHIPPED
White
Common
BLW
Black
High
COOL
Yellow
{
Med---High
SPARE
Blue*
Med---Low
SPARE
Red*
Low
HEAT
* 1/5 HP motor models: BLUE to HEAT, RED to SPARE
{
Not available on 1/5 HP motors.
NOTE:
Continuous blower is the HEAT speed.
f. Repeat steps a through e.
g. When correct input rate and temperature rise is
achieved, turn gas valve ON/OFF switch to OFF.
h. Remove manometer or similar device from gas valve.
i. Reinstall manifold pressure tap plug in gas valve.
FIRE HAZARD
Failure to follow this warning could result in personal
injury, death and/or property damage.
Reinstall manifold pressure tap plug in gas valve to
prevent gas leak.
!
WARNING
j. Reinstall blower access door if removed.
k. Turn gas valve ON/OFF switch to ON.
PG
8J
/M
