Carrier Infinity 48DT Series Installation Instructions Manual page 24

f. Multiply result ofstep f .byBtu heating value o fthe gas
toobtain total measured input shown inTable 4.(Consult
the local gas supplier if the heating value o fgas isnot
known).
EXAMPLE: Assume a 90,000 h igh stage i nput u nitis being
installed. Assume that t hesize of thedial i s 2 cubic f t.,one
revolution takes 84sec., and tire heating value o fthe gas i s1050
Btu/fl3. Proceed as follows:
a.84sec. tocomplete one revolution
b.3600/84 =42.9
c.42.9 x2=85.8 f t3ofgas f low/hr.
d.85.8 x1050 = 90,090 Btuh input.
Inthis example, the nominal input r ate forhigh stage is90,000
Btu/hr, so the high stage manifold pressure iscorrectly set.
If the measured high stage rate istoolow, i ncrease the manifold
pressure toincrease rate. If the measured high s tage rate i stoo high,
decrease the manifold pressure todecrease rate.
NOTE:Double-check that U ser Interface isrunning onhigh stage
gas h eat while clocking the lowstage firing rate.
7.Verify p roper high stage gas h eat temperature rise.
a.Furnace must operate within rise range l isted o nrating
plate.
b.Make s ure a ccess panel isre-installed onthe unit.
c.Measure supply and return t emperatures as close t othe
unit a s possible. Subtract the return temperature from the
supply temperature todetermine rise.Rise s hould fall
within t he range specified onthe rating plate.
NOTE: If the temperature rise isoutside the rating plate r ange, first
check:
a.Gas i nput forlow and high stage gas h eat operation.
b.Derate foraltitude, if applicable.
c.Return a ndsupply ducts for excessive restrictions
causing static pressures inexcess of.5in.wc.
d.Make s ure m odel plug isinstalled.
8.Final Check
a.Turn o ffgas t ounit
b.Remove manometer from pressure tap.
c.Replace pipe plug onmanifold (See Fig. 1 9).
d.Turn o ngas t ounit.
e.Check forleaks.
CHECK G AS INPUT ( PROPANE GAS)
Refer topropane kitinstallation instructions forproperly checking
gas i nput.
NOTE: For i nstallations below 2 ,000 ft., r efer tothe unit r ating plate
forproper propane conversion kit.For i nstallations above 2,000 ft,
contact your d istributor forproper propane conversion kit.
CHECK BURNER FLAME
Withburner access panel removed, observe theunitheating
operation. Watch the burner flames tosee i fthey are light b lue and
soft i nappearance, and that t he flames are approximately the same
foreach burner. Propane willhave b lue f lame ( See Fig. 2 0). Refer
tothe Maintenance section forinformation onburner removal.
MAN]FOLD P[PE PLUG
Fig. 19 - Burner Assembly
C99019
BURNER FLAME
]FOLD
099021
Fig. 20 - Monoport Burner
LIMIT SWITCHES
Normally closed limit switch (LS) completes the control circuit.
Should the leaving-air temperature rise above the maximum
allowable temperature, the limit switch opens and the control circuit
"breaks." Any interruption in the control circuit instantly closes the
gas valve and stops gas flow to the burners and pilot. The blower
motor continues to run until LS resets. The furnace board STATUS
LED will display STATUS CODE 33.
When the air temperature at the limit switch drops to the
low-temperature setting of the limit switch, the switch closes and
completes the control circuit. The direct-spark ignition system
cycles and the unit returns to normal heating operation.
ROLLOUT SWITCH
The function of the rollout switch is to close the main gas valve in
the event of flame rollout. The switch is located above the main
burners. When the temperature at the rollout switch reaches the
maximum allowable temperature, the control circuit trips, closing
the gas valve and stopping gas flow to the burners. The indoor fan
motor (IFM) continues to run until switch is reset. The furnace board
STATUS LED will display STATUS CODE 33.
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