JOHNSON CONTROLS
93
SECTION 5 – SEQUENCE OF OPERATION
FORM 100.50-NOM12
ISSUE DATE: 04/02/2019
5
• The 24 VAC inputs are provided from the V1
terminals of the ignition controls, except for
the 1A high, which is provided when the PS2
pressure switch closes. PS2 pressure switch
closes when the induced draft motor on fur-
nace section 1 is on high speed.
• 24 VAC must be present at TB1-1 and TB1-7
for the multiplexer to function properly. DS1
LED is lit when 24 VAC is present at TB1-1
and TB1-7.
2. TB2 and LED Light DS7
• TB2 is used to output a 0–5 VDC signal back
to the IPU board.
• TB2 outputs on staged and modulating gas
heat:
• TB2-1: 5 VDC power from IPU board
• TB2-2: 5 VDC common to IPU board
• TB2-3: 0–5 VDC signal back to IPU
board
• 5 VDC must be present at TB2-1 and TB2-2
for the multiplexer to function properly. DS7
LED is lit when 5 VDC is present at TB2-1
and TB2-2.
• When 5 VDC is not present at TB2-1 and
TB2-2, neither DS1 or DS7 are lit.
TABLE 36 -
STAGED GAS HEAT 0–5 VDC OUTPUTS TO IPU
MIN VOLTS DC
MAX VOLTS DC
FURNACE 1 STATUS FURNACE 2 STATUS FURNACE 3 STATUS
0.086
0.166
OFF
OFF
OFF
0.224
0.313
ON
OFF
OFF
0.361
0.461
OFF
ON
OFF
0.499
0.609
ON
ON
OFF
0.637
0.756
OFF
OFF
ON
0.774
0.904
ON
OFF
ON
0.912
1.051
OFF
ON
ON
1.050
1.199
ON
ON
ON
TABLE 37 -
MODULATING GAS HEAT 0–5 VDC OUTPUTS TO IPU
MIN VOLTS
DC
MAX
VOLTS DC
MODULATING
FURNACE 1A STATUS
FURNACE 1A
STATUS
FURNACE 2
STATUS
FURNACE 3
STATUS
FURNACE 1B
STATUS
0.086
0.166
OFF
OFF
OFF
OFF
OFF
0.224
0.313
ON
OFF
OFF
OFF
OFF
0.361
0.461
OFF
ON
OFF
OFF
OFF
0.499
0.609
ON
ON
OFF
OFF
OFF
0.637
0.756
OFF
OFF
ON
OFF
OFF
0.774
0.904
ON
OFF
ON
OFF
OFF
0.912
1051
OFF
ON
ON
OFF
OFF
1.050
1.199
ON
ON
ON
OFF
OFF
1.187
1.346
OFF
OFF
OFF
ON
OFF
1.325
1.494
ON
OFF
OFF
ON
OFF
1.463
1.641
OFF
ON
OFF
ON
OFF
1.600
1.789
ON
ON
OFF
ON
OFF
1.738
1.936
OFF
OFF
ON
ON
OFF
1.876
2.084
ON
OFF
ON
ON
OFF
2.013
2.231
OFF
ON
ON
ON
OFF
2.151
2.379
ON
ON
ON
ON
OFF
2.289
2.526
OFF
OFF
OFF
OFF
ON
2.426
2.674
ON
OFF
OFF
OFF
ON
2.564
2.821
OFF
ON
OFF
OFF
ON
2.702
2.969
ON
ON
OFF
OFF
ON
2.839
3.116
OFF
OFF
ON
OFF
ON
2.977
3.264
ON
OFF
ON
OFF
ON