41
Table 9 – Blower Off Delay Setup Switch
DESIRED HEATING MODE
BLOWER OFF DELAY (SEC.)
SETUP SWITCH (SW --- 7 AND
--- 8) POSITION
SW1--- 7 S W 1 --- 8
90 OFF OFF
120 ON OFF
150 OFF ON
180 ON ON
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 for high-- heat
1.6--in. wc for low-- heat
* Furnace is shipped with No. 43 orifices. In this exam-
ple
all main burner orifices are the correct size and do not
need
to be changed to obtain proper input rate.
2. Adju st manifold pressure to obtain low fire input rate. (See
Fig. 53.)
a. Turn g as valve ON/OFF switch to OFF.
b. Remove manifold pressure tap plug from gas valve.
c. Connect a water column manometer or similar device
to manifold pressure tap.
d. Turn gas valve ON/OFF switch to ON.
e. Move setup SW1—2 on furnace control to ON
position to lock furnace in low--heat operation. (See
Table 8 and Fig. 25.)
f. Manually close blower door switch.
g. Jumper R and W/W1 thermostat connections on
control to start furnace. (See Fig. 25.)
h. Remove regulator adjustment cap from low heat gas
valve pressu re regulator (See Fig. 53.) and turn
low--heat adjusting screw (3/16 or smaller flat--tipped
screwdriver) counterclockwise (out) to decrease input
rate or clockwise (in) to increase input rate.
NOTE: DO NOT set low-- heat manifold pressure less than
1.4--in wc or more than 1.7--in. wc for natural gas. If manifold
pressure is outside this range, change main burner orifices.
i. Install low--heat regulator adjustment cap.
j. Leave manometer or similar device connected and
proceed to Step 4.
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.
3. Verify natural gas low-- heat input rate by clocking meter.
NOTE: Gas valve regulator adjustment caps 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 low--heat operation.
c. Measure time (in sec) for gas meter to complete 1
revolution 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 (Btuh/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
low-- heat input is achieved. Re--install lowheat
regulator seal cap on gas valve.
4. Set low heat temperature rise. The furnace must operate
within the temperature rise ranges specified on the furnace
rating plate. Do not exceed temperature rise ranges
specified on furnace rating plate for high--and low--fire.
Determine the temperature rise as follows:
NOTE: Blower access door must be installed when taking
temperature rise reading. Leaving blower access door off will
result in incorrect temperature measurements.
a. Verify unit is running in low-- heat per Step 4. 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 particularly
important with straight-- run ducts.
b. When thermometer readings stabilize, subtract
return--air temperature from supply --air temperature to
determine air temperature rise.
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
315A
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