5188235-YIM-E-0518
56 Johnson Controls Ducted Systems
Checking Gas Input
Natural Gas
1. Turn off all other gas appliances connected to the gas meter.
2. With the furnace turned on, measure the time needed for
one revolution of the hand on the smallest dial on the
meter. A typical gas meter usually has a 1/2 or a 1 cubic
foot test dial.
3. Using the number of seconds for each revolution and the
size of the test dial increment, find the cubic feet of gas
consumed per hour from the Gas Rate - Cubic Feet Per
Hour (Table 25).
If the actual input is not within 5% of the furnace rating (with
allowance being made for the permissible range of the regulator
setting), replace the orifice spuds with spuds of the proper size.
NOTE: To find the Btu input, multiply the number of cubic feet
of gas consumed per hour by the Btu content of the gas
in your particular locality (contact your gas company for
this information - it varies widely from city to city.)
Adjustment Of Temperature Rise
The temperature rise (or temperature difference between the
return air and the heated air from the furnace) must lie within
the range shown on the rating plate and the data in the Gas
Heat Application Table 10.
After the temperature rise has been determined, the cfm can be
calculated as follows:
After about 20 minutes of operation, determine the furnace
temperature rise. Take readings of both the return air and the
heated air in the ducts (about six feet from the furnace) where
they will not be affected by radiant heat. Increase
the blower
cfm to decrease
the temperature rise; decrease the blower cfm
to increase the rise. Refer to the In Door Blower Specification
Table 17.
Troubleshooting (Simplicity Lite Only)
On calls for cooling, if the compressors are operating but the
supply air blower motor does not energize after a short delay
(the room thermostat fan switch is in the “AUTO” position).
1. Turn the thermostat fan switch to the ON position. If the
supply air blower motor does not energize, go to Step 3.
2. If the blower motor runs with the fan switch in the ON
position but will not run after the compressor has energized
when the fan switch is in the AUTO position, check the
room thermostat for contact between R and G in the AUTO
position during calls for cooling.
3. If the supply air blower motor does not energize when the
fan switch is set to ON, check that line voltage is being
supplied to the contacts of the M2, contactor, and that the
Table 25: Gas Rate-Cubit Feet per Hour
1
1. By actual measurement, it takes 38 seconds for the hand on
the 1-cubic foot dial to make a revolution with a 100,000 Btuh
furnace running. Using this information, located 38 seconds
in the first column in the table above. Read across to the
column headed “1 Cubic Foot”, where you will see that 95
cubic feet of gas per hour are consumed by the furnace at
that rate. Multiply 95 X 1050 (the Btu rating of the gas
obtained from the local gas company). The result is 99,750
Btuh, which is close to the 100,000 Btuh rating of the furnace.
Seconds for
One Rev.
Size of Test Dial
1/2 cu. ft. 1 cu. ft.
10 180 360
12 150 300
14 129 257
16 113 225
18 100 200
20 90 180
22 82 164
24 75 150
26 69 138
28 64 129
30 60 120
32 56 113
34 53 106
36 50 100
38 47 95
40 45 90
42 43 86
44 41 82
46 39 78
48 37 75
50 36 72
52 35 69
54 34 67
56 32 64
58 31 62
60 30 60
Troubleshooting of components may require opening
the electrical control box with the power connected to
the unit. Use extreme care when working with live
circuits! Check the unit nameplate for the correct line
voltage and set the voltmeter to the correct range before
making any connections with line terminals.
When not necessary, shut off all electric power to the
unit prior to any of the following maintenance
procedures so as to prevent personal injury.
Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and
dangerous operation which could cause injury to person
and/or damage unit components. Verify proper
operation after servicing.
CFM
Btuh Input x 0.8
=
108..xFTempRise
o
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