Step 3—Start-up Procedures
1. Component test—The furnace features a component test
system to help diagnose a system problem in the case of a
component failure. To initiate the component test procedure,
ensure that there are no thermostat inputs to the control and all
time delays have expired. Short the TWIN/TEST terminal to
ground or C
OM
for 1 to 4 sec. (See Fig. 17.)
NOTE:
The component test feature will not operate if the control
is receiving any thermostat signals or until all time delays have
expired.
The component test sequence is as follows:
a. The furnace control checks itself, operates the inducer
motor on low speed for 7 sec and on high speed for 7 sec,
then stops.
b. The hot surface ignitor is energized for 15 sec, then
de-energized.
c. The blower motor operates on low-gas-heat/heat pump
low-heat/low-cool/continuous fan speed for 7 sec, then
stops.
d. The blower motor operates on high-gas heat for 7 sec, then
stops. The gas valve and humidifier terminal HUM are not
energized for safety reasons.
e. The blower motor operates on heat pump high-heat/high-
cool speed for 7 sec, then stops.
NOTE:
The EAC terminals are energized when the blower is
energized.
2. After all connections have been made, purge gas lines and
check for leaks.
Never purge a line into a combustion chamber. Never use
matches, candles, flame, or other sources of ignition for the
purpose of checking leakage. Use a soap-and-water solution
to check for leakage. A failure to follow this warning can
cause a fire, explosion, personal injury, or death.
3. To operate furnace, follow procedures on operating instruc-
tions label attached to furnace.
4. With furnace operating, set thermostat below room tempera-
ture and observe that furnace goes off. Set thermostat above
room temperature and observe that furnace restarts.
Step 4—Adjustments
1. Set gas input rate.
Furnace gas input rate on rating plate is for installations at
altitudes up to 2000 ft.
In the U.S.A., input rating for altitudes above 2000 ft must be
reduced by 4 percent for each 1000 ft above sea level.
In Canada, input rating must be derated by 10 percent for
altitudes of 2000 ft to 4500 ft above sea level.
Furnace input rate must be within ±2 percent of input on
furnace rating plate.
2. Determine natural gas orifice size and manifold pressure for
correct input.
a. Obtain yearly heat value average (at installed altitude) from
local gas supplier.
b. Obtain yearly specific gravity average from local gas
supplier.
c. Verify furnace model. Table 9 can only be used for model
58UXT furnaces.
d. Find installation altitude in Table 9.
NOTE:
For Canada altitudes of 2000 to 4500 ft, use U.S.A.
altitudes of 2001 to 3000 ft in Table 9.
e. Find closest natural gas heat value and specific gravity in
Table 9.
f. Follow heat value and specific gravity lines to point of
intersection to find orifice size and low- and high-heat
manifold pressure settings for proper operation.
EXAMPLE: (0–2000 ft altitude)
Heating value = 1075 Btu/cu ft
Specific gravity = 0.62
Therefore: Orifice No. 45
Manifold pressure 3.6-in. wc for high heat
* Furnace is shipped with No. 45 orifices. In this example,
all main burner orifices are the correct size and do not need
to be changed to obtain proper input rate.
g. Check and verify burner orifice size in furnace. NEVER
ASSUME ORIFICE SIZE; ALWAYS CHECK AND
VERIFY.
3. Adjust manifold pressure to obtain input rate.
a. Remove caps that conceal adjustment screws for low- and
high-heat gas valve regulators. (See Fig. 21.)
b. Move setup switch SW-2 on control center to ON position.
(See Fig. 18.) This keeps furnace locked in low-heat
operation.
c. Jumper R and W/W1 thermostat connections on control
center to start furnace.
d. Turn low-heat adjusting screw (5/64 hex Allen wrench)
counterclockwise (out) to decrease input rate or clockwise
(in) to increase input rate.
NOTE:
DO NOT set low-heat manifold pressure less than 1.3-in.
wc or more than 1.7-in. wc for natural gas. If manifold pressure is
outside this range, change main burner orifices.
DO NOT bottom out gas valve regulator adjusting screw.
This can result in unregulated manifold pressure and result in
excess overfire and heat exchanger failures.
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.
Table 8—Altitude Derate Multiplier for U.S.A.
ALTITUDE
(FT)
PERCENT 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
28—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.
17