826081-XIM-C-0214
Johnson Controls Unitary Products
37
1.
Remove the screws holding either end of the manifold to
the burner supports.
2.
Open the union fitting in the gas supply line just upstream
of the unit gas valve and downstream from the main
manual shut-off valve.
3.
Remove the gas piping closure panel.
4.
Disconnect wiring to the gas valves and spark ignitors.
Remove the manifold-burner gas valve assembly by lifting
up and pulling back.
Burners are now accessible for service.
Reverse the above procedure to replace the assemblies. Make
sure that burners are level and seat at the rear of the heat
exchanger.
Burner Air Shutter Adjustment
Adjust burner shutters so no yellow flame is observed in the
heat exchanger tubes.
Checking Gas Input
Natural Gas
Seconds for one
rev.
Size of Test Dial
1/2 cu. ft.
1 cu. ft.
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 23).
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
CFM
Btuh Input x 0.8
=
108
.
.
x F Temp Rise
o
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 3.
After the temperature rise has been determined, the Volumetric
Flow Rate 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
Volumetric Flow Rate to decrease the temperature rise;
decrease the blower Volumetric Flow Rate to increase the rise.
Refer to the Blower Motor and Drive Data Table 17.
Figure 22: Typical Flame Appearance
Table 23: Gas Rate - Cubic 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 col-
umn 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.
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
