EXAMPLE:
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
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
2.When thermometer readings stabilize, subtract
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 | SIZE OF TEST DIAL | ||||
FOR 1 | 1 | 2 | 5 | FOR 1 | 1 | 2 | 5 |
REVOLUTION | cu ft | cu ft | cu ft | REVOLUTION | cu ft | cu ft | cu ft |
10 | 360 | 720 | 1800 | 50 | 72 | 144 | 360 |
11 | 327 | 655 | 1636 | 51 | 71 | 141 | 355 |
12 | 300 | 600 | 1500 | 52 | 69 | 138 | 346 |
13 | 277 | 555 | 1385 | 53 | 68 | 136 | 340 |
14 | 257 | 514 | 1286 | 54 | 67 | 133 | 333 |
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 | 124 | 29 | 58 | 145 |
TABLE 13—SPEED SELECTOR
|
| FACTORY- |
COLOR | SPEED | SHIPPED |
|
| CONNECTION |
Black | High | Cool |
Yellow (When Present) | Medium High | Spare |
Blue | Medium Low | Heat |
Red | Low | Spare |
White | Common | COM |
|
|
|
TABLE 14–BLOWER OFF DELAY SETUP POSITION
PINS | 1 AND 2 | 2 AND 3 | 3 AND 4 | 4 AND 5 |
Time (in sec) | 90 | 120 | 150 | 180 |
WARNING: Disconnect
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
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