On the display
The panel gives no display and the unit will not operate. The troubleshooting table lists the problem under the exact wording NO DISPLAY ON PANEL. UNIT WILL NOT OPERATE. Both the 2020 and the 2024 edition of the table carry the entry in this single wording; the manuals print no other variant of it.
What it means
The message describes the condition itself: the panel is dark and the unit cannot be operated. The manual locates the fault in the unit's control-power chain — the supply feeding the 24 VAC Control Transformer, the 24 VAC wiring on to the Microboard, the Control Transformer itself, and the IPU II & I/O Board or the Display Board. Even the short in the wire to the temp. sensors or pressure transducers is traced at that chain: the manual isolates it by unplugging the connections at the IPU II & I/O Board.
Why it appears
- No 115 VAC to 24 VAC Transformer — the 2024 edition words the same first cause as no 220VAC to 24VAC Transformer.
- No 24 VAC to the Microboard.
- The Control Transformer is defective and gives no 24 VAC output.
- A short in the wire to the temp. sensors or to the pressure transducers.
- The IPU II & I/O Board or the Display Board is defective.
What to check
- Check the wiring and fuse 1FU.
- Check the wiring of the emergency stop contacts 5 to L of the XTBC2 Terminal Block.
- Replace the Control Transformer.
- Check the wiring from the Control Transformer to the Microboard.
- Replace the Control Transformer if it is defective with no 24 VAC output.
- Unplug the connections at the IPU II & I/O Board to isolate the short in the wire to the temp. sensors or pressure transducers.
- Replace the IPU II & I/O Board or the Display Board — first,
Contact Johnson Controls Service before replacing circuit Boards!
Questions engineers ask
Why does my YORK YLAA show no display and will not run?
The troubleshooting table gives five causes: no 115 VAC to the 24 VAC Transformer, no 24 VAC to the Microboard, a defective Control Transformer with no 24 VAC output, a short in the wire to the temp. sensors or pressure transducers, or a defective IPU II & I/O Board or Display Board. The 2024 edition words the first supply as 220VAC.
Which fuse does the YORK YLAA manual check when the panel is blank?
Fuse 1FU. It is checked together with the wiring for the cause the table words as no 115 VAC to 24 VAC Transformer.
Do I have to call Johnson Controls Service before changing a board?
The manual says to contact Johnson Controls Service before replacing circuit boards; the boards named for this fault are the IPU II & I/O Board and the Display Board.
Where is the emergency stop wiring checked on this fault?
The manual checks the wiring of the emergency stop contacts 5 to L of the XTBC2 Terminal Block.
Messages next to this one
Source
Written from the manufacturer's manuals for the YORK YLAA; every number and designation on this page is checked against them before publication. The row of the manual this message comes from:
All YORK YLAA messages: fault codes · YORK YLAA documentation · YORK manuals