29
airfl ow rate for the capacity. Detailed operation is
described in the cooling unit installation instruc-
tions and control manual.
Verifying and Adjusting
Temperature Rise
Verify that the temperature rise through the
furnace is within the range specifi ed on the
furnace rating plate. Temperature rises outside
the specifi ed range could result in premature
heat exchanger failure.
Place temperature measuring device in the return
and supply air stream as close to the furnace
as possible. The device on the supply air side
must be shielded from direct radiation from the
heat exchanger to avoid false readings. Adjust
all registers and duct dampers to the desired
position and run the furnace for fi fteen minutes
before taking any temperature readings. The
temperature rise is the difference between the
supply and return air temperatures.
Verifying Burner Operation
To verify operation of the burners, make sure
that the blower compartment door is in place
and that there is power to the furnace. Set
the thermostat above room temperature and
observe the ignition sequence. The fl ame can
be observed through the small clear window
on the burner box. The fl ames should be blue,
without yellow tips. Flames should extend from
each burner without lifting, curling, or fl oating.
After verifying ignition, set the thermostat below
room temperature and verify that the burner fl ame
extinguishes completely.
Verifying Operation of the Supply
Air Limit Switch
To verify operation of the supply air limit switch,
make sure that the blower door is in place and
that there is power to the furnace. Completely
block the return airfl ow to the furnace by install-
ing a close-off plate in place of or upstream
of the fi lter(s). Set the thermostat above room
temperature and verify that the Sequence of
Operation is as described in these instructions.
The supply air limit switch should function to
turn off the gas valve within approximately fi ve
minutes. The circulating air and combustion blow-
ers should continue to run when the supply air
limit switch opens. Remove the close-off plate
immediately after the supply air limit switch opens.
If the furnace operates for more than fi ve minutes
with no return air, set the thermostat below room
Table 11. Gas Flow Rate
GAS FLOW RATE (CUBIC FEET PER HOUR)
TIME FOR
ONE REVOLUTION
(SECONDS)
CUBIC FEET PER REVOLUTION OF
METER
TIME FOR
ONE REVOLUTION
(SECONDS)
CUBIC FEET PER REVOLUTION OF
METER
1
5
10
1
5
10
24
150
750
1500
74
49
243
486
26
138
692
1385
76
47
237
474
28
129
643
1286
78
46
231
462
30
120
600
1200
80
45
225
450
32
113
563
1125
82
44
220
439
34
106
529
1059
84
43
214
429
36
100
500
1000
86
42
209
419
38
95
474
947
88
41
205
409
40
90
450
900
90
40
200
400
42
86
429
857
92
39
196
391
44
82
409
818
94
38
191
383
46
78
391
783
96
38
188
375
48
75
375
750
98
37
184
367
50
72
360
720
100
36
180
360
52
69
346
692
102
35
176
353
54
67
333
667
104
35
173
346
56
64
321
643
106
34
170
340
58
62
310
621
108
33
167
333
60
60
300
600
110
33
164
327
62
58
290
581
112
32
161
321
64
56
281
563
114
32
158
316
66
55
273
545
116
31
155
310
68
53
265
529
118
31
153
305
70
51
257
514
120
30
150
300
72
50
250
500
