Adjustments; Set Temperature Rise; Blower Off Delay (Heat Mode); Set Thermostat Heat Anticipator - Bryant 345MAV Installation, Start-Up, And Operating Instructions Manual

c. Measure time (in sec) for gas meter test dial to complete
1 revolution.
d. Refer to Table 9 for cu ft of gas per hr.
e. Multiply gas rate (cu ft/hr) X heating value (Btu/cu ft)
using natural gas heating value from local gas
utility/supplier.
TABLE 9—GAS RATE (CU FT/HR)
SECONDS SIZE OF TEST DIAL
1 2 5
FOR 1
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
EXAMPLE:
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 9)
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 unit rating plate. Recommended operation is
at midpoint of rise or above. Failure to follow this caution
may result in condensing or overheating the heat ex-
changers.
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.
SECONDS SIZE OF TEST DIAL
1 2 5
FOR 1
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
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.
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. 27.) Select desired blower motor speed
lead from 1 of the other terminals and relocate it to HEAT
terminal. See Table 10 for lead color identification. Recon-
nect original lead on SPARE terminal.
Follow this same procedure for proper COOL speed selec-
tion.
TABLE 10–SPEED SELECTOR
COLOR
Black
Yellow (When Present)
Blue
Red
White
C. Blower Off Delay (Heat Mode)
The main blower off time delay period is factory-set at 135 sec and
is not field-adjustable.
D. Set Thermostat Heat Anticipator
Thermostat heat anticipator must be set to match amp draw of
components in R-W circuit. Accurate amp draw measurements can
be obtained at thermostat subbase terminals R and W.
Fig. 42 illustrates an easy method of obtaining these measure-
ments. Amp reading should be taken after blower motor has
started. See thermostat manufacturer's instructions for adjusting
heat anticipator and for varying heating cycle length.
THERMOSTAT SUBBASE
TERMINALS WITH
THERMOSTAT REMOVED
10 TURNS
5.0 AMPS ON AMMETER
EXAMPLE:
10 TURNS AROUND JAWS
Fig. 42—Amp Draw Check with Ammeter
—38—
FACTORY-
SPEED SHIPPED
CONNECTION
High
Medium High
Medium Low
Low
Common
HOOK-AROUND
VOLT/AMMETER
R Y W G
FROM UNIT 24-VOLT
TERMINAL BLOCK
= 0.5 AMPS FOR THERMOSTAT SETTING
Cool
Spare
Heat
Spare
Com
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