Bryant 312A Installation, Start-Up, Operating And Service And Maintenance Instructions page 38

SECONDS
FOR
1
REVOLUTION
10
11
12
13
14
15
16
17
18
19
20
21
22
23
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26
27
28
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c. Adjust air temperature rise by adjusting blower speed.
Increase blower speed to reduce temperature rise.
Decrease blower speed to increase temperature rise. For
low heat, speed selection can be low (factory setting),
med- -low, or med (5- -speed blowers only).
d. Remove thermostat jumpers and release Blower Access
Door Switch.
e. To change motor speed selection for low heat, remove
blower motor lead from control LO- -HEAT terminal.
(See Fig. 34.) Select desired blower motor speed lead
from 1 of the other terminals and relocate it to the
LO- -HEAT terminal. (See Table 13 for lead color
identification). Reconnect original lead to SPARE
terminal.
f. Repeat steps a through e.
CAUTION
!
FURNACE OVERHEATING HAZARD
Failure to follow this caution may result in reduced furnace
life.
Recheck temperature rise. It must be within limits specified
on the rating plate. Recommended operation is at the
midpoint of rise range or slightly above.
g. When correct low heat input rate and temperature rise is
achieved, proceed to Step 6.
6. Adjust Manifold Pressure to Obtain High Heat Rate
Table 12 – Gas Rate (cu ft/hr)
SIZE OF TEST DIAL
C F C F C
1 U T 2 U T 5 U
360 720 1800
327 655 1636
300 600 1500
277 555 1385
257 514 1286
240 480 1200
225 450 1125
212 424 1059
200 400 1000
189 379 947
180 360 900
171 343 857
164 327 818
157 313 783
150 300 750
144 288 720
138 277 692
133 267 667
129 257 643
124 248 621
120 240 600
116 232 581
113 225 563
109 218 545
106 212 529
103 206 514
100 200 500
97 195 486
95 189 474
92 185 462
90 180 450
88 176 439
86 172 429
84 167 419
82 164 409
80 160 400
78 157 391
76 153 383
75 150 375
73 147 367
SECONDS
FOR
1
F
T
REVOLUTION
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120
a. Remove high fire regulator adjustment cap from gas
valve pressure regulator.
b. Manually close blower access door switch.
c. Jumper R, W/W1 and W2 thermostat connections on
control to run furnace in high heat. (See Fig. 34.)
d. d. Turn high- -heat adjusting screw (3/16 in. or smaller flat
tipped screwdriver) counterclockwise (out) to decrease
input rate or clockwise (in) to increase rate.
e. Re- -install high- -fire adjustment caps.
f. Leave manifold or similar device connected and proceed
to Step 7.
NOTE: DO NOT set high- -heat manifold pressure less than
3.2- -in. wc or more than 3.8- -in. wc for natural gas. If manifold
pressure is outside this range, change main burner orifices.
7. Verify natural gas high heat input rate by clocking meter.
NOTE: Gas valve regulator adjustment caps must be in place for
proper input to be clocked.
a. Turn off all other gas appliances and pilots served by the
meter.
b. Run for 3 minutes in high- -heat operation.
c. Measure time (in sec) for gas meter to complete 1
revolution and note reading.
d. Refer to Table 12 for cubic ft of gas per hr.
e. Multiply gas rate cu ft/hr by heating value (Btuh/cu ft)
to obtain input.
NOTE: Using the 2 cu. ft or 5 cu. ft gas meter dial provides
greater accuracy in verifying gas input rate.
38
SIZE OF TEST DIAL
C F C F C F
1 U T 2 U T 5 U
72 144 360
71 141 355
69 138 346
68 136 340
67 133 333
65 131 327
64 129 321
63 126 316
62 124 310
61 122 305
60 120 300
58 116 290
56 112 281
54 109 273
53 106 265
51 103 257
50 100 250
48 97 243
47 95 237
46 92 231
45 90 225
44 88 220
43 86 214
42 84 209
41 82 205
40 80 200
39 78 196
38 76 192
38 75 188
37 74 184
36 72 180
35 71 178
35 69 173
34 68 170
33 67 167
33 65 164
32 64 161
31 62 155
30 60 150
T