JOHNSON CONTROLS
150
FORM 150.73-NM1
ISSUE DATE: 09/04/2020
SECTION 9 – SERVICE AND TROUBLESHOOTING
TABLE 38 - TROUBLESHOOTING
PROBLEM CAUSE SOLUTION
NO DISPLAY ON PANEL.
UNIT WILL NOT OPERATE
1. No 115 VAC to 24 VAC Transformer.
2. No 24 VAC to Microboard.
3. Control Transformer defective, no 24
VAC output.
4. Short in wire to temp. sensors or
pressure transducers.
5. Defective IPU II and I/O Board or the
Display Board.
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 Transformer to
Microboard.
3. Replace Control Transformer.
4. Unplug connections at IPU I and I/O
Board to isolate.
5. Replace IPU II and I/O Board or the
Display Board.
Contact Johnson
Controls Service be-
fore replacing Circuit
Boards!
“FLOW SWITCH/REM STOP NO RUN
PERMISSIVE”
1. No air ow.
2. Air Proving Switch improperly
installed.
3. Defective Air Proving Switch.
4. Remote cycling device open.
1. Check air ow.
2. Check that the Air Proving Switch is
installed according to manufacturer’s
instructions.
3. Replace Air Proving Switch.
4. Check cycling devices connected to
terminals 13 and 14 of the XTBC1
Terminal Block.
“LOW SUCTION PRESSURE FAULT”
1. Improper suction pressure cutouts
adjustments.
2. Low refrigerant charge.
3. Fouled Filter Dryer.
4. TXV defective.
5. Reduced air ow.
6. Defective Suction Pressure
Transducer/Low Pressure Switch or
wiring.
7. LLSV defective.
1. Adjust per recommended settings.
2. Repair leak if necessary and add
refrigerant.
3. Change Dryer/Core.
4. Replace TXV.
5. Check air ow.
6. Replace Transducer/Low Pressure
Switch or faulty wiring. See
SECTION 9 – SERVICE AND
TROUBLESHOOTING for pressure/
voltage formula.
7. Replace LLSV.
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