Bryant 373LAV User Manual

Page 19

3. Set thermostat heat anticipator.

The thermostat heat anticipator must be set to match the
amp draw of the electrical components in the R-W circuit.
Accurate amp draw readings can be obtained at thermostat
subbase terminals R and W. Fig. 19 illustrates an easy
method of obtaining the actual amp draw. The amp reading
should be taken after the blower motor has started. See the
thermostat manufacturer’s instructions for adjusting the
heat anticipator and for varying the heating cycle length.

NOTE:

When using an electronic thermostat, set cycle rate for 3

cycles per hr.

Check Safety Controls

The flame sensor, gas valve, and pressure switch were all checked
in the Start-Up Procedures section as part of normal operation.

1. Check primary limit control.

This control shuts off the combustion control system and
energizes the circulating-air blower motor if the furnace
overheats.

The preferred method of checking the limit control is to
gradually block off the return air after the furnace has been
operating for a period of at least 5 minutes. As soon as the

limit has shut off the burners, the return-air opening should
be unblocked. By using this method to check the limit
control, it can be established that the limit is functioning
properly and operates if there is a motor failure.

2. Check blocked vent safeguard switch.

The purpose of this control is to permit the safe shutdown
of the furnace during certain blocked vent conditions.

a. Disconnect power to furnace and remove vent connector

from furnace outlet collar. Be sure to allow time for vent
pipe to cool down before removing.

b. Restore power to furnace and set room thermostat above

room temperature.

c. After normal start-up, allow furnace to operate for 2

minutes, then block flue outlet 100 percent. Furnace
should cycle off within 2 minutes.

d. Remove blockage and reconnect vent pipe to furnace

outlet collar.

e. Wait 5 minutes and then reset blocked vent safeguard

switch.

3. Check pressure switch.

This control proves operation of draft inducer blower.

a. Turn off 115-v power to furnace.

b. Remove control door and disconnect inducer motor lead

wires from wire harness.

c. Turn on 115-v power to furnace.

d. Set thermostat to "call for heat" and wait 1 minute. When

pressure switch is functioning properly, hot surface
igniter should NOT glow and control diagnostic light
flashes a status code 31. If hot surface igniter glows
when inducer motor is disconnected, shut down furnace
immediately. Determine reason pressure switch did not
function properly and correct condition.

e. Turn off 115-v power to furnace.

f. Reconnect inducer motor wires, replace control door, and

turn on 115-v power to furnace.

4. Check auxiliary limits (when used).

TABLE 9—GAS RATE (CU FT/HR)

SECONDS

FOR 1

REVOLUTION

SIZE OF TEST DIAL

SECONDS

FOR 1

REVOLUTION

SIZE OF TEST DIAL

cu ft

10
11
12
13
14

360
327
300
277
257

720
655
600
555
514

1800
1636
1500
1385
1286

50
51
52
53
54

72
71
69
68
67

144
141
138
136
133

360
355
346
340
333

15
16
17
18
19

240
225
212
200
189

480
450
424
400
379

1200
1125
1059
1000

947

55
56
57
58
59

65
64
63
62
61

131
129
126
124
122

327
321
316
310
305

20
21
22
23
24

180
171
164
157
150

360
343
327
313
300

900
857
818
783
750

60
62
64
66
68

60
58
56
54
53

120
116
112
109
106

300
290
281
273
265

25
26
27
28
29

144
138
133
129
124

288
277
267
257
248

720
692
667
643
621

70
72
74
76
78

51
50
48
47
46

103
100

97
95
92

257
250
243
237
231

30
31
32
33
34

120
116
113
109
106

240
232
225
218
212

600
581
563
545
529

80
82
84
86
88

45
44
43
42
41

90
88
86
84
82

225
220
214
209
205

35
36
37
38
39

103
100

97
95
92

206
200
195
189
185

514
500
486
474
462

90
92
94
96
98

40
39
38
38
37

80
78
76
75
74

200
196
192
188
184

40
41
42
43
44

90
88
86
84
82

180
176
172
167
164

450
439
429
419
409

100
102
104
106
108

36
35
35
34
33

72
71
69
68
67

180
178
173
170
167

45
46
47
48
49

80
78
76
75
73

160
157
153
150
147

400
391
383
375
367

110
112
116
120

33
32
31
30

65
64
62
60

164
161
155
150

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TABLE 10—SPEED SELECTOR

COLOR

SPEED

FACTORY-

ATTACHED TO

Black

High

COOL

Yellow

(When present)

Medium-High

SPARE

Blue

Medium-Low

HEAT

Red

Low

SPARE

White

Common

L2/COM

Fig. 19—Amp Draw Check With Ammeter

A96316

Y W G

10 TURNS

THERMOSTAT SUBBASE
TERMINALS WITH
THERMOSTAT REMOVED
(ANITICIPATOR, CLOCK, ETC.,
MUST BE OUT OF CIRCUIT.)

HOOK-AROUND
AMMETER

EXAMPLE:

5.0 AMPS ON AMMETER
10 TURNS AROUND JAWS

0.5 AMPS FOR THERMOSTAT

ANTICIPATOR SETTING

FROM UNIT 24-V
CONTROL TERMINALS

—19—

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