915SB: Installation, Start-up, Operating and Service and Maintenance Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
50
c. Run furnace for 3 minutes.
d. Measure time (in sec) for gas meter to complete one revolution
and note reading. The 2 or 5 cubic feet dial provides a more
accurate measurement of gas flow.
for cubic ft. of gas per hr.
f. Multiply gas rate cu ft./hr by heating value (BTUh/cu ft.) to
obtain input rate.
g. If clocked rate does not match required input from Step 1,
increase manifold pressure to increase input or decrease manifold
pressure to decrease input. Repeat steps b through e until correct
input is achieved. Re-install regulator seal cap on gas valve.
3. Restore furnace to normal operating condition.
a. Turn gas valve ON/OFF switch to OFF.
b. Remove water column manometer or similar device from
manifold pressure tap.
c. Tighten set screw on manifold tower pressure tap with 3/32-in.
hex wrench, or if 1/8-in. NPT plug was removed, apply pipe
dope sparingly to end of plug and reinstall in the gas valve.
d. Turn gas valve ON/OFF switch to ON.
e. Check for gas leaks and verify furnace operation.
Adjust Temperature Rise
NOTE:
Blower door must be installed when taking temperature rise
reading. Leaving blower door off will result in incorrect temperature
measurements, due to possible changes in duct static pressure and
airflow.
This furnace must operate within the temperature rise ranges specified
on the furnace rating plate. Determine the air temperature as follows:
1. Place duct thermometers in return and supply ducts as close to
furnace as possible. Be sure thermometers do not “see” heat
exchangers so that radiant heat does not affect thermometer
readings. This is particularly important with straight run ducts.
2. When thermometer readings stabilize, subtract return-air
temperature from supply-air temperature to determine temperature
rise.
If the temperature rise is outside this range, check the following:
3. Gas input rate.
4. Derate for altitude applicable.
5. Return and supply ducts for excessive restrictions causing static
pressures greater than 0.50-in. w.c. (125 Pa)
6. Adjust temperature rise by adjusting blower speed. Reference
- Air Delivery for available heating airflow ranges.
NOTICE
!
For 40,000 BTUH models through 120,000 BTUH models:
DO NOT
set manifold pressure less than 2.8-in. w.c. (697 Pa) or more than 3.8 in.
w.c. (947 Pa) for natural gas. If required manifold pressure is outside
this range, change main burner orifices to obtain manifold pressure in
this range.
Table 18 – Gas Rate (CU ft./hr)
SEC
FOR 1
REV
SIZE OF TEST DIAL
SEC
FOR 1
REV
SIZE OF TEST DIAL
1 Cu
Ft.
2 Cu
Ft.
5 Cu
Ft.
1 Cu
Ft.
2 Cu
Ft.
5 Cu
Ft.
10
360
720
1800
55
65
131
327
11
327
655
1636
56
64
129
321
12
300
600
1500
57
63
126
316
13
277
555
1385
58
62
124
310
14
257
514
1286
59
61
122
305
15
240
480
1200
60
60
120
300
16
225
450
1125
62
58
116
290
17
212
424
1059
64
56
112
281
18
200
400
1000
66
54
109
273
19
189
379
947
68
53
106
265
20
180
360
900
70
51
103
257
21
171
343
857
72
50
100
250
22
164
327
818
74
48
97
243
23
157
313
783
76
47
95
237
24
150
300
750
78
46
92
231
25
144
288
720
80
45
90
225
26
138
277
692
82
44
88
220
27
133
267
667
84
43
86
214
28
129
257
643
86
42
84
209
29
124
248
621
88
41
82
205
30
120
240
600
90
40
80
200
31
116
232
581
92
39
78
196
32
113
225
563
94
38
76
192
33
109
218
545
96
38
75
188
34
106
212
529
98
37
74
184
35
103
206
514
100
36
72
180
36
100
200
500
102
35
71
178
37
97
195
486
104
35
69
173
38
95
189
474
106
34
68
170
39
92
185
462
108
33
67
167
40
90
180
450
110
33
65
164
41
88
176
439
112
32
64
161
42
86
172
429
116
31
62
155
43
84
167
419
120
30
60
150
44
82
164
409
124
29
58
145
45
80
160
400
129
28
56
140
46
78
157
391
133
27
54
135
47
76
153
383
138
26
52
130
48
75
150
375
144
25
50
125
49
73
147
367
150
24
48
120
50
72
144
360
157
23
46
115
51
71
141
355
164
22
44
110
52
69
138
346
171
21
42
105
53
68
136
340
180
20
40
100
54
67
133
333
WARNING
!
FIRE HAZARD
Failure to follow this warning could result in personal injury, death,
and/or property damage.
Manifold pressure tap set screw must be tightened and 1/8-in. NPT pipe
plug must be installed to prevent gas leaks.
CAUTION
!
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in:
S
Overheating the heat exchangers or condensing flue gases in heat
exchanger areas not designed for condensate.
S
Shortened furnace life
S
Component damage.
Temperature rise must be within limits specified on furnace rating plate.
Recommended operation is at midpoint of rise range or slightly above.
