EXAMPLE: (0—2000 ft altitude)
Furnace input from rating plate is 100,000 Btuh.
Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 975 Btu/cu ft
Time for 1 revolution of 2-cu ft dial = 70 sec
Gas rate = 103 cu ft/hr (from Table 12)
Btu heating input = 103 X 975 = 100,425 Btuh
In this example, the orifice size and manifold pressure
adjustment is within 2 percent of the furnace input rate.
B. Set Temperature Rise
CAUTION: Temperature rise must be within limits
specified on furnace rating plate. Recommended opera-
tion is at midpoint of rise range or slightly above. Failure
to follow this caution may result in primary and second-
ary heat exchangers failure.
Determine and adjust air temperature rise as follows:
1. Place thermometers in return and supply ducts as close to
furnace as possible. Be sure thermometers do not see heat
exchanger so that radiant heat does not affect readings. This
practice is particularly important with straight-run ducts.
2. When thermometer readings stabilize, subtract return-air
temperature from supply-air temperature to determine air
temperature rise.
3. Adjust temperature rise by adjusting blower speed. Increase
blower speed to reduce temperature rise. Decrease blower
speed to increase temperature rise.
TABLE 12—GAS RATE (CU FT/HR)
SECONDS
SIZE OF TEST DIAL SECONDS
FOR 1
1
2
5
REVOLUTION
cu ft
cu ft
cu ft
10
360
720
1800
11
327
655
1636
12
300
600
1500
13
277
555
1385
14
257
514
1286
15
240
480
1200
16
225
450
1125
17
212
424
1059
18
200
400
1000
19
189
379
947
20
180
360
900
21
171
343
857
22
164
327
818
23
157
313
783
24
150
300
750
25
144
288
720
26
138
277
692
27
133
267
667
28
129
257
643
29
124
248
621
30
120
240
600
31
116
232
581
32
113
225
563
33
109
218
545
34
106
212
529
35
103
206
514
36
100
200
500
37
97
195
486
38
95
189
474
39
92
185
462
40
90
180
450
41
88
176
439
42
86
172
429
43
84
167
419
44
82
164
409
45
80
160
400
46
78
157
391
47
76
153
383
48
75
150
375
49
73
147
367
SIZE OF TEST DIAL
FOR 1
1
2
5
REVOLUTION
cu ft
cu ft
cu ft
50
72
144
360
51
71
141
355
52
69
138
346
53
68
136
340
54
67
133
333
55
65
131
327
56
64
129
321
57
63
126
316
58
62
124
310
59
61
122
305
60
60
120
300
62
58
116
290
64
56
112
281
66
54
109
273
68
53
106
265
70
51
103
257
72
50
100
250
74
48
97
243
76
47
95
237
78
46
92
231
80
45
90
225
82
44
88
220
84
43
86
214
86
42
84
209
88
41
82
205
90
40
80
200
92
39
78
196
94
38
76
192
96
38
75
188
98
37
74
184
100
36
72
180
102
35
71
178
104
35
69
173
106
34
68
170
108
33
67
167
110
33
65
164
112
32
64
161
116
31
62
155
120
30
60
150
124
29
58
145
TABLE 13—SPEED SELECTOR
COLOR
Black
Yellow (When Present)
Blue
Red
White
TABLE 14–BLOWER OFF DELAY SETUP POSITION
PINS
Time (in sec)
WARNING: Disconnect 115-v electrical power before
changing speed tap. Failure to follow this warning could
result in personal injury.
4. To change blower motor speed selections for heating mode,
remove blower motor lead from control center HEAT
terminal. (See Fig. 31.) Select desired blower motor speed
lead from 1 of the other motor leads and relocate it to HEAT
terminal. See Table 13 for lead color identification. Recon-
nect original lead on SPARE terminal.
Follow this same procedure for proper selection of COOL
speed selection.
C. Blower Off Delay (Heat Mode)
The blower off delay has 4 adjustable settings from 90 sec to 180
sec. (See Table 14.) The blower off delay jumpers are located on
the furnace control board (See Fig. 31). To change the blower off
delay setting, move the jumper from one set of pins on the control
board to the pins used for the desired blower off delay. Factory
blower off delay setting is 120 sec.
D. Set Thermostat Heat Anticipator
When using a nonelectronic thermostat, the thermostat heat
anticipator must be set to match amp draw of the electrical
components in R-W circuit. Accurate amp draw readings can be
obtained at thermostat subbase terminals R and W. Fig. 53
illustrates an easy method of obtaining actual amp draw. The amp
reading should be taken after blower motor has started and furnace
is heating. Connect ammeter wires as shown in Fig. 53.
The thermostat anticipator ahould NOT be in the circuit while
measuring current. If thermostat has no subbase, the thermostat
must be disconnected from R and W wires during current
measurement. See thermostat manufacturer's instructions for ad-
justing heat anticipator and for varying heating cycle length.
For an electronic thermostat, set cycle rate for 3 cycles per hour.
CHECK SAFETY CONTROLS
This section covers the safety controls that must be checked before
the installation is complete. The flame sensor, gas valve, and
pressure switch were all checked in the Start-up procedure section
as part of normal operation.
—44—
FACTORY-
SPEED
SHIPPED
CONNECTION
High
Medium High
Medium Low
Low
Common
1 AND 2
2 AND 3
3 AND 4
90
120
150
Cool
Spare
Heat
Spare
C
OM
4 AND 5
180