Carrier DOWNFLOW HORIZONTAL 2-SPEED - Manual (Page 17)

e. Move setup switch SW-2 to OFF position after completing
low-heat adjustment.
f. Jumper R and W2 thermostat connections on control center.
(See Fig. 14.) This keeps furnace locked in high-heat
operation.
g. Turn high-heat adjusting screw (5/64 hex Allen wrench)
counterclockwise (out) to decrease input rate or clockwise
(in) to increase rate.
NOTE: DO NOT set high-heat manifold pressure less than 3.2-in.
wc or more than 3.8-in. wc for natural gas. If manifold pressure is
outside this range, change main burner orifices.
h. When correct input is obtained, replace caps that conceal
gas valve regulator adjustment screws. Main burner flame
should be clear blue, almost transparent. (See Fig. 20.)
i. Remove jumper R to W2.
4. Verify natural gas input rate by clocking gas meter.
a. Calculate high-altitude adjustment (if required).
UNITED STATES
At altitudes above 2000 ft, this furnace has been approved
for a 4 percent derate for each 1000 ft above sea level. See
Table 9 for derate multiplier factor and example.
EXAMPLE:
85,000 Btuh input furnace installed at 4300 ft.
Furnace Input
Rate at
Sea Level
X
Derate
Multiplier
Factor
=
Furnace Input Rate
at Installation
Altitude
85,000 X 0.82 = 69,700
CANADA
At installation altitudes from 2000 to 4500 ft, this furnace
must be derated 10 percent by an authorized Gas Conver-
sion Station or Dealer. To determine correct input rate for
altitude, see example above and use 0.82 as derate multi-
plier factor.
b. Check that gas valve adjustment caps are in place for
proper input to be clocked.
c. Obtain yearly heat value average for local gas supply.
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.
d. Check and verify orifice size in furnace. NEVER AS-
SUME THE ORIFICE SIZE. ALWAYS CHECK AND
VERIFY.
e. Turn off all other gas appliances and pilots.
f. Move setup switch SW-2 to ON position. (See Fig. 17.)
This keeps furnace locked in low-heat operation.
g. Jumper R to W/W1.
h. Let furnace run for 3 minutes in low-heat operation.
i. Measure time (in sec) for gas meter to complete 1 revolu-
tion. Note reading.
j. Refer to Table 10 for cubic ft of gas per hr.
k. Multiply gas rate cu ft/hr by heating value (Btu/cu ft).
l. Move setup switch SW-2 to OFF position and jumper R and
W2 thermostat connections. (See Fig. 17.) This keeps
furnace locked in high-heat operation. Repeat items h
through k for high-heat operation.
EXAMPLE: (High-heat operation at 0—2000 ft altitude)
Furnace input from rating plate is 85,000 Btuh
Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 1050 Btu/cu ft
Time for 1 revolution of 2-cu ft dial = 92 sec
Gas rate = 80 cu ft/hr (from Table 10)
Btu heating input = 80 X 1050 = 84,000 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.
m. Remove jumper across R, W/W1, and W2 thermostat
connections to terminate call for heat.
5. Set temperature rise.
Place SW-2 in ON position. Jumper R to W/W1 and W2 to
check high-gas-heat temperature rise. To check low-gas-heat
temperature rise, remove jumper to W2. Determine air tem-
perature rise for both high and low heat using the following
steps. DO NOT exceed temperature rise ranges specified on
unit rating plate for high and low heat.
DO NOT redrill orifices. Improper drilling (burrs, out-of-
round holes, etc.) can cause excessive burner noise and
misdirection of burner flames. This can result in flame
impingement of burners and heat exchangers, causing
failures.
A93059
BURNER
ORIFICE
Table 9—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 8—12 0.90
3001—4000 12—16 0.86
4001—5000 16—20 0.82
5001—6000 20—24 0.78
6001—7000 24—28 0.74
7001—8000 18—32 0.70
8001—9000 32—36 0.66
9001—10,000 36—40 0.62
* Derate multiplier factor is based on midpoint altitude for altitude range.
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