Johnson Controls 100 Series - FIGURE 49 - Digital Multiplexor Control Board

JOHNSON CONTROLS
92
FORM 100.50-NOM12
ISSUE DATE: 04/02/2019
SECTION 5 – SEQUENCE OF OPERATION
LD28126
FIGURE 49 - DIGITAL MULTIPLEXOR CONTROL BOARD
• TB1-5: Not used on staged gas heat
• TB1-6: Not used on staged gas heat
• TB1-7: 24 VAC common from T5 trans-
former
• TB1 inputs on modulating gas heat:
• TB1-1: 24 VAC input from T5 trans-
former (DS1 is lit)
• TB1-2: 24 VAC input from furnace 1A,
DS2 is lit (375 MBH heating capacity)
• TB1-3: 24 VAC input from furnace 1A
high, DS3 is lit (375 MBH heating ca-
pacity)
• TB1-4: 24 VAC input from furnace 2,
DS4 is lit (750 MBH heating capacity)
• TB1-5: 24 VAC input from furnace 3,
DS5 is lit (1125 MBH heating capacity)
• TB1-6: 24 VAC input from furnace 1B,
DS6 is lit (375, 750, or 1125 MBH heat-
ing capacity)
• TB1-7: 24 VAC common from T5 trans-
former
Digital Multiplexer Control Board
• A Series 100 unit equipped with either staged or
modulating gas heat utilizes a digital multi-plexer
control board.
• The digital multiplexer control monitors numer-
ous 24 VAC inputs and then uses these inputs to
send a 0–5 VDC signal back to the IPU board.
• The IPU board uses this 0–5 VDC signal to deter-
mine the status of the different furnace sections.
Understanding and Troubleshooting the
Digital Multiplexer Control Board
1. TB1 and LED Lights DS1-DS6
• TB1 is used for the 24 VAC inputs from the
different sections in the unit.
• TB1 inputs on staged gas heat:
• TB1-1: 24 VAC input from T5 trans-
former (DS1 is lit)
• TB1-2: 24 VAC input from furnace 1,
DS2 is lit (375 MBH heating capacity)
• TB1-3: 24 VAC input from furnace 2,
DS3 is lit (750 MBH heating capacity)
• TB1-4: 24 VAC input from furnace 3,
DS4 is lit (1125 MBH heating capacity)