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11 - Are flame rollout switches tripped? If flame rollout
switches are tripped, call the service technician for in
spection.
Heating Sequence Of Operation
(follow steps below or see Figure 29 for more detail)
1 - When thermostat calls for heat, combustion air blower
starts.
2 - Combustion air pressure switch proves blower opera
tion. Switch is factory-set and requires no adjustment.
3 - After a 15-second prepurge, the hot surface ignitor en
ergizes.
4 - After a 20-second ignitor warm-up period, the gas
valve solenoid opens. A 4-second trial for ignition peri
od begins.
5 - Gas is ignited, flame sensor proves the flame, and the
combustion process continues.
6 - If flame is not detected after first ignition trial, the igni
tion control will repeat steps 3 and 4 four more times
before locking out the gas valve (flame failure mode).
The ignition control will then automatically repeat steps
1 through 6 after 60 minutes.
7 - To interrupt the 60-minute internal lockout period, move
thermostat from “Heat” to “OFF” then back to “Heat.”
Heating sequence then restarts at step 1.
Gas Pressure Adjustment
Gas Flow (Approximate)
TABLE 7
GAS METER CLOCKING CHART
80AF1UH
Unit
Seconds for One Revolution
Natural
LP
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
-045
80
160
200
400
-070
55
110
136
272
-090
41
82
102
204
-110
33
66
82
164
-135
27
54
68
136
Natural-1000 btu/cu ft LP-2500 btu/cu ft
Furnace should operate at least 5 minutes before check
ing gas flow. Determine time in seconds for
two
revolu
tions of gas through the meter. (Two revolutions assures a
more accurate time.)
Divide by two
and compare to time
in table 7 below. If manifold pressure matches table 9 and
rate is incorrect, check gas orifices for proper size and re
striction. Remove temporary gas meter if installed.
NOTE
- To obtain accurate reading, shut off all other gas
appliances connected to meter.
Supply Pressure Measurement
A threaded plug on the inlet side of the gas valve provides
access to the supply pressure tap. Remove the threaded
plug, install a field-provided barbed fitting and connect a
manometer to measure supply pressure. See table 9 for
proper line pressure. Replace the threaded plug after mea
surements have been taken.
Manifold Pressure Measurement
1 - Remove the threaded plug from the outlet side of the
gas valve and install a field-provided barbed fitting.
Connect to a manometer to measure manifold pres
sure.
2 - Start unit and allow 5 minutes for unit to reach steady
state.
3 - While waiting for the unit to stabilize, observe the
flame. Flame should be stable and should not lift from
burner. Natural gas should burn blue.
4 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
9.
NOTE
- Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to remove
barbed fitting and replace threaded plug.
Proper Combustion
Furnace should operate a minimum 15 minutes with cor
rect manifold pressure and gas flow rate before checking
combustion. Take combustion sample beyond the flue out
let and compare to the tables below.
The maximum car
bon monoxide reading should not exceed 50 ppm.
TABLE 8
80AF1UH
Unit
CO
2
%
For Nat
CO
2
%
For L.P.
-045
7.2 - 7.8
7.5 - 9.0
-070
-090
-110
-135
High Altitude
The manifold pressure may require adjustment and com
bustion air pressure switch may need replacing to ensure
proper combustion at higher altitudes. Refer to table 9 for
manifold pressure and table 10 for pressure switch change
and gas conversion kits.
IMPORTANT
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
