Bryant 987MB - Page 56

987MB: 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.
56
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.
When setup switch SW1-4 is ON, operation will be near the high end of
the rise range for improved comfort.
Furnace must operate within ranges of temperature rise specified on the
furnace rating plate. Determine air temperature rise as follows:
1. Place thermometers in return and supply ducts as near 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.
NOTE: Temperature rise can be determined for Minimum Heat,
Intermediate Heat and Maximum Heat operation by locking the furnace
in each mode of operation. The mode of operation is based on the
position of Set-up switch SW1-2 and SW4-2 on the furnace control
board.
The furnace is capable of automatically providing proper airflow to
maintain the temperature rise within the range specified on furnace
rating plate. If temperature rise is outside this range, proceed as follows:
1. Check gas input for minimum, intermediate and maximum heat
operation.
2. Check derate for altitude if applicable.
3. Check all return and supply ducts for excessive restrictions causing
static pressure greater than 0.5-in. w.c.
4. Ensure Min/Int Heat Rise Adjust switch SW1-3 on furnace control
is in ON position when a bypass humidifier is used. See Table 60
for switch location.
5. Check Troubleshooting Guide for Variable-Speed Step Modulating
Condensing Furnaces.
6. Verify correct model plug is installed.
To lock the furnace in Minimum Heat:
1. Turn SW1-2 ON at the furnace control. Setup switch SW4-2 must
be OFF.
2. Connect a jumper across R and W/W1 at the thermostat terminals at
the furnace control.
3. Allow the burners to ignite and the blower to turn on.
4. Allow the supply temperature to stabilize and verify the proper rise
range.
If the temperature rise is too high or too low in Minimum Heat:
1. Remove jumpers from R and W/W1.
2. Wait until the blower off delay is completed.
3. Turn 115 VAC power off.
4. Check the position of setup switch SW1-3. When set to ON, airflow
is raised 18% for Minimum Heat and for Intermediate Heat.
Factory default position is OFF.
5. Turn 115 VAC power on.
6. Re-check Minimum Heat Temperature Rise
To lock the furnace in Intermediate Heat:
1. Turn SW1-2 OFF and SW4-2 ON at the furnace control.
2. Connect a jumper across R and W/W1 at the thermostat terminals at
the furnace control.
3. Allow the burners to ignite and the blower to turn on.
4. Allow the supply temperature to stabilize and verify the proper rise
range.
If the temperature rise is too high or too low in Intermediate Heat:
1. Remove jumpers from R and W/W1.
2. Wait until the blower off delay is completed.
3. Turn 115 VAC power off.
4. Check the position of setup switch SW1-3. When set to ON, airflow
is raised 18% for Minimum Heat and for Intermediate Heat.
Factory default position is OFF.
5. Turn 115 VAC power on.
6. Re-check Minimum Heat Temperature Rise.
15
240 480 1200 55 65 131 327
16
225 450 1125 56 64 129 321
17
212 424 1059 57 63 126 316
18
200 400 1000 58 62 124 310
19
189 379 947 59 61 122 305
20
180 360 900 60 60 120 300
21
171 343 857 62 58 116 290
22
164 327 818 64 56 112 281
23
157 313 783 66 54 109 273
24
150 300 750 68 53 106 265
25
144 288 720 70 51 103 257
26
138 277 692 72 50 100 250
27
133 267 667 74 48 97 243
28
129 257 643 76 47 95 237
29
124 248 621 78 46 92 231
30
120 240 600 80 45 90 225
31
116 232 581 82 44 88 220
32
113 225 563 84 43 86 214
33
109 218 545 86 42 84 209
34
106 212 529 88 41 82 205
35
103 206 514 90 40 80 200
36
100 200 500 92 39 78 196
37
97 195 486 94 38 76 192
38
95 189 474 96 38 75 188
39
92 185 462 98 37 74 184
40
90 180 450 100 36 72 180
41
88 176 439 102 35 71 178
42
86 172 429 104 35 69 173
43
84 167 419 106 34 68 170
44
82 164 409 108 33 67 167
45
80 160 400 110 33 65 164
46
78 157 391 112 32 64 161
47
76 153 383 116 31 62 155
48
75 150 375 120 30 60 150
49
73 147 367
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.
Table 17 – Gas Rate (CU ft./hr) (Continued)