Page 25
Heating Sequence Of Operation
(follow steps below and see Figure 21)
1 - When thermostat calls for heat, combustion air
blower starts.
2 - Combustion air pressure switch proves blower
operation. Switch is factory-set and requires no
adjustment.
3 - After a 15-second prepurge, the hot surface ignitor
energizes.
4 - After a 20-second ignitor warm-up period, the gas
valve solenoid opens. A 4-second trial for ignition
period begins.
the combustion process continues.
ignition control will repeat steps 3 and 4 four
more times before locking out the gas valve
control will then automatically repeat steps 1 through
6 after 60 minutes.
7 - To interrupt the 60-minute “WATCHGUARD” 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 9
GAS METER CLOCKING CHART
ML80DFE
Unit
Seconds For One Revolution
Natural LP/Propane
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-
-
tions of gas through the meter. (Two revolutions assures a
more accurate time.) Divide by two and compare to time
in table 10 below. If manifold pressure matches table 12
restriction. Remove temporary gas meter if installed.
NOTE - To obtain accurate reading, shut o 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
manometer to measure supply pressure. Furnace should
operate at least 5 minutes before checking supply pres-
sure. See table 12 for proper supply pressure. Replace
the threaded plug after measurements have been taken.
Manifold Pressure Measurement
1 - Remove the threaded plug from the outlet side of
pressure.
2 - Start unit and allow 5 minutes for unit to reach steady
state.
3 - While waiting for the unit to stabilize, observe the
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 12.
NOTE - Shut unit o and remove manometer as soon as
an accurate reading has been obtained. Take care to re-
move barbed tting and replace threaded plug.
Proper Combustion
Furnace should operate a minimum 15 minutes with cor-
-
let and compare to the tables below. The maximum car-
bon monoxide reading should not exceed 100 ppm.
TABLE 10
ML180DFE Unit CO
2
%
Nat CO
2
% LP
-045
6.8 - 7.4 7.5 - 9.0
-070
-090
-110
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 12
for manifold pressure and table 13 for pressure switch
change and gas conversion kits.
WARNING
as an accurate reading has been obtained. Take care to
replace pressure tap plug.
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