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SECTION 9 – SERVICE AND TROUBLESHOOTING
TABLE 31 - TROUBLESHOOTING
PROBLEM
NO DISPLAY ON PANEL.
UNIT WILL NOT OPERATE
"FLOW SWITCH/REM STOP NO
RUN PERMISSIVE"
144
TROUBLESHOOTING
CAUSE
1. No 115VAC to 24 VAC Trans-
former.
2. No 24VAC to Microboard.
3. Control Transformer defective,
no 24VAC output.
4. Short in wire to temp. sensors
or pressure transducers.
5. Defective IPU II & I/O Board or
the Display Board.
1. No air flow.
2. Air Proving Switch improperly
installed.
3. Defective Air Proving Switch.
4. Remote cycling device open.
FORM 150.73-NM2
ISSUE DATE: 09/07/2020
SOLUTION
1a. Check wiring and fuse 1FU.
1b. Check wiring emergency stop
contacts 5 to L of XTBC2
Terminal Block.
1c. Replace Control Transformer.
2. Check wiring Control Trans-
former to Microboard.
3. Replace Control Transformer.
4. Unplug connections at IPU I &
I/O Board to isolate.
5. Replace IPU II & I/O Board or
the Display Board.
Contact Johnson Con-
trols Service before re-
placing Circuit Boards!
1. Check air flow.
2 Check that the Air Proving
Switch is installed according to
manufacturer's instructions.
3. Replace Air Proving Switch.
4. Check cycling devices connect-
ed to terminals 13 and 14 of the
XTBC1 Terminal Block.
JOHNSON CONTROLS
CONT'D
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Table of Contents
Troubleshooting
