Bryant 340MAV B. Set Temperature Rise, Gasrate Cu Ft/Hr, Speedselector, Check Safety Controls

Models: 340MAV

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B. Set Temperature Rise

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

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 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.

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Bryant 340MAV instruction manual B. Set Temperature Rise, Gasrate Cu Ft/Hr, Speedselector, Bloweroff Delay Setup Position