47
NOTE
: Clocking gas input rate MUST always be performed
with the burner box cover INSTALLED.
c. Check that gas valve adjustment caps are in place for
proper input to be clocked.
d. Obtain average heat value (at altitude) from local gas
supplier.
NOTE
: Be sure heating value of gas used for calculations is
correct for your altitude. Consult local gas utility for altitude
adjustment of gas heating value.
e. Check and verify orifice size in furnace. NEVER
ASSUME THE ORIFICE SIZE. ALWAYS CHECK
AND VERIFY.
f. Turn off all other gas appliances and pilots.
g. Move setup switch SW1--2 to ON position. (See Fig.
33.) This keeps furnace locked in low--heat operation.
;;
;;
BURNER FLAME
BURNER
MANIFOLD
A89020
Fig. 53
---
Burner Flame
TABLE 12—ALTITUDE DERATE MULTIPLIER FOR
U.S.A.
ALTITUDE
(FT)
% OF
DERATE
DERATE MULTIPLIER
FACTOR FOR U.S.A.*
0—2000
0
1.00
2001—3000
4—6
0.95
3001—4000
6—8
0.93
4001—5000
8—10
0.91
5001—6000
10—12
0.89
6001—7000
12—14
0.87
7001—8000
14—16
0.85
8001—9000
16—18
0.83
9001—10,000
18—20
0.81
* Derate multiplier factor is based on midpoint altitude for altitude range
h. Jumper R to W/W1.
i. Let furnace run for 3 minutes in low--heat operation.
j. Measure time (in sec) for gas meter to complete 1
revolution. Note reading.
k. Refer to Table 13 for cubic ft of gas per hr.
l. Multiply gas rate cu ft/hr by heating value (Btu/cu ft).
m. Move setup switch SW1--2 to OFF position and
jumper R and W/W1 and W2 thermostat connections.
(See Fig. 33.) This keeps furnace locked in high--heat
operation. Repeat items i through l for high--heat
operation.
UNIT DAMAGE HAZARD
Failure to follow this caution may result in component
damage due to flame impingement of burners and heat
exchangers.
DO NOT redrill orifices. Improper drilling (burrs,
out--of--round holes, etc.) can cause excessive burner noise
and misdirection of burner flames. (See Fig. 52.)
CAUTION
!
EXAMPLE:
(High--heat operation at 0 -- 2000 ft altitude)
Furnace input from rating plate is 100,000 Btuh
Btuh heating input = Btuh/cu ft X cu ft/hr
Heating value of gas = 975 Btuh/cu ft
Time for 1 revolution of 2--cu ft dial = 70 sec
Gas rate = 103 cu ft/hr (from Table 13)
Btuh heating input = 103 X 975 = 100,425 Btuh
In this example, the orifice size and manifold pressure
adjustment is within
±
2 percent of the furnace input rate.
NOTE
: Measured gas inputs (high heat and low heat) must be
within
±
2 percent of that stated on furnace rating plate when
installed at sea level or derated per that stated above when
installed at higher altitudes.
n. Remove jumper across R, W/W1, and W2 thermostat
connections to terminate call for heat.
SET TEMPERATURE RISE
UNIT DAMAGE HAZARD
Failure to follow this caution may result in overheating the
heat exchangers or condensing flue gases in heat exchanger
areas not designed for condensate.
Temperature rise must be within limits specified on unit
rating plate. Operation is within a few degrees of midpoint
of rise range when setup switch SW1--4 is OFF.
CAUTION
!
Furnace must operate within ranges of temperature rise specified
on the furnace rating plate. Determine air temperature rise as
follows:
1. Place thermometers in return and supply ducts as near
furnace as possible. Be sure thermometers do not see heat
exchanger so that radiant heat does not affect readings.
This practice is particularly important with straight--run
ducts.
2. When thermometer readings stabilize, subtract return--air
temperature from supply--air temperature to determine air
temperature rise.
NOTE
:
Temperature rise can be determined for low--heat
operation by placing setup switch SW1--2 on furnace control in
ON position. For high--heat operation, place setup switch SW1--2
in OFF position and jumper R--W2 on furnace control. DO NOT
forget to return setup switch to OFF position and remove R--W2
jumper upon completion of testing. (See Fig. 33 for switch and
terminal location.)
58U
VB
