Adjustments - International comfort products F9MXT0401410A Service And Technical Support Manual

SERVICE AND TECHNICAL SUPPORT MANUAL

Adjustments

! WARNING
FIRE HAZARD
Failure to follow this warning could result in personal
injury, death and/or property damage.
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.
CAUTION
!
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in reduced furnace
life.
DO NOT redrill orifices.
outïofïround holes, etc.) can cause excessive burner
noise and misdirection of burner flames. This can result in
flame impingement of heat exchangers, causing failures.
(See Figure 2)
Figure 2 Orifice Hole
For proper operation and long term reliability the furnace input
rate must be within +2 percent of input rate on furnace rating
plate.
The gas input rate on rating plate is for installation at altitudes
up to 2000 ft. (610 M).
In the U.S.A., the input rating for altitudes above 2000 ft. (610
M) must be reduced by 2 percent for each 1000 ft. (305 M)
above sea level refer to Table 1.
In Canada, the input rating must be derated by 5 percent for
altitudes of 2000 ft. (610 M) to 4500 ft. (1372 M) above sea
level.
To adjust manifold pressure to obtain the proper input rate, first,
determine if the furnace has the correct orifice installed. At
higher altitudes or different gas heat contents, it may be
necessary to change the factory orifice to a different orifice.
Tables have been provided in the furnace Service and
Technical Manual to match the required orifice to the manifold
pressure to the heat content and specific gravity of the gas. to
do this:
a. Obtain average yearly gas heat value (at installed
altitude) from local gas supplier.
b. Obtain average yearly gas specific gravity from local
gas supplier.
c. Find installation altitude in Table 2.
440 04 4321 02
Improper drilling (burrs,
BURNER
ORIFICE
A93059
Specifications subject to change without notice.
d. Find closest natural gas heat value and specific
gravity in Table 2.
e. Follow heat value and specific gravity lines to point of
intersection to find orifice size and lowïand highïheat
manifold pressure settings for proper operation.
f. Check and verify burner orifice size in furnace.
NEVER ASSUME ORIFICE SIZE. ALWAYS CHECK
AND VERIFY.
Table 1 Altitude Derate Multiplier for U.S.A.
ALTITUDE PERCENT
FT. (M) OF DERATE
0–2000
0
(0ï610)
2001–3000
4ï6
(610ï914)
3001–4000
6ï8
(914ï1219)
4001–5000
8ï10
(1219ï1524)
5001–6000
10ï12
(1524ï1829)
6001–7000
12ï14
(1829ï2134)
7001–8000
14ï16
(2134ï2438)
8001–9000
16ï18
(2438ï2743)
9001–10,000
18ï20
(2743ï3048)
* Derate multiplier factors are based on midpoint altitude for altitude range.
NOTE: For Canadian altitudes of 2000 to 4500 ft. (610 to
1372 M), use USA altitudes of 2001 to 3000 ft. (610 to 914
M)
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 burrïfree and squarely
aligned orifice hole is essential for proper flame characteristics.
g. Replace orifice with correct size, if required by
Table 2. Use only factoryïsupplied orifices. See
EXAMPLE.
EXAMPLE: 0 - 2000 ft. (0 - 609.6M) altitude
Heating value = 1050 Btu/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 44
Manifold pressure: 3.4-in. w.c. for high heat, 1.4-in. w.c. for low
heat
* Furnace is shipped with No. 44 orifices. In this example, all
main burner orifices are the correct size and do not need to be
changed to obtain proper input rate.
1. Adjust manifold pressure to obtain low fire input rate.
(See Figure 3)
a. Turn gas 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 switch (TT) on furnace control to ON
position to lock furnace in lowïheat operation. (See
Figure 4 and Figure 15)
f. Manually close blower door switch.
g. Jumper R and W/W1 thermostat connections on
control to start furnace. (See Figure 4)
h. Remove regulator adjustment cap from low heat gas
valve pressure regulator (See Figure 3) and turn
lowïheat adjusting screw (3/16 or smaller flatïtipped
Gas Furnace: (F/G)9MXT
DERATE MULTIPLIER
FACTOR*
1.00
0.95
0.93
0.91
0.89
0.87
0.85
0.83
0.81
5