York YCUL0020 Installation, Operation And Maintenance Manual page 156

SECTION 9 – SERVICE AND TROUBLESHOOTING
Table 31 - Troubleshooting
PROBLEM
NO DISPLAY ON PANEL. UNIT
WILL NOT OPERATE.
FLOW SWITCH/REM STOP NO
RUN PERMISSIVE
LOW SUCTION PRESSURE
FAULT
HIGH DISCHARGE PRESSURE
FAULT
156
Troubleshooting
CAUSE
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.
1. No air flow.
2. Air Proving switch incorrectly
installed.
3. Defective Air Proving switch.
4. Remote cycling device open.
1. Improbeforesuction pressure
cutouts adjustments.
2. Low refrigerant charge.
3. Fouled filter dryer.
4. TXV defective.
5. Reduced air flow
6. Defective suction pressure
transducer/low pressure switch
or wiring.
7. LLSV defective
1. Condenser fans not operating or
operating backwards.
2. Too much refrigerant.
3. Air in refrigerant system.
4. Defective discharge pressure
transducer.
SOLUTION
1a. Check wiring and fuse 1FU.
1b. Check wiring emergency stop contacts 5 to
L of TB1 Terminal Block.
1c. Replace Control Transformer.
2. Check wiring Control Transformer to
Microboard.
3. Replace Control Transformer.
4. Unplug connections at IPU II and I/O Board
to isolate.
5. Replace IPU II and I/O Board or the Display
Board.
Contact Johnson Controls
Service before replacing 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 connected to
terminals 13 and 14 of the CTB1 Terminal
Block.
1. Adjust beforerecommended settings.
2. Repair leak if necessary and add refrigerant.
3. Change dryer/core.
4. Replace TXV.
5. Check air flow
6. Replace transducer/low pressure switch or
faulty switch or wiring. See Service section
for pressure/voltage formula.
7. Replace LLSV
1. Check fan motor, and contactors. Ensure fan
blows air upward.
2. Remove refrigerant.
3. Evacuate and recharge system.
4. Replace discharge pressure transducer. See
Service section for pressure/voltage formula.
JOHNSON CONTROLS
Form 150.63-NM9
Issue date: 5/20/2021