On the display
The panel reads COMPRESSOR(S) WON'T START. This is the exact wording the YLAA troubleshooting tables print for this condition; the manuals list no other variant of the message.
What it means
The message states that the unit's compressors are not starting. The manual treats this first as a question of demand rather than a fault: when the cooling demand is not great enough, the compressors simply stay off, and the action the manual gives for that case is No problem
, pointing to the Installation Manual for an understanding of compressor operation and capacity control. Only when a demand for cooling exists does the message point to hardware: a defective water temperature sensor, a contactor/overload failure, or a compressor failure.
Why it appears
- Demand not great enough — the compressors stay off because the call for cooling is too small; the manual marks this case as no problem.
- Defective water temperature sensor.
- Contactor/Overload failure.
- Compressor failure.
What to check
- Decide first whether demand is simply not great enough. If it is, there is no problem; the manual directs you to the Installation Manual to understand compressor operation and capacity control.
- Compare the temperature shown on the display with a thermometer. The two readings should be within +/- 2 degrees of each other.
- Refer to the RWT/LWT temperature/voltage table in the Service section (Table 26) for the water temperature sensor's expected values.
- If the cause is a contactor/overload failure, replace the defective part.
- If the cause is compressor failure, diagnose the cause of the failure and replace the compressor.
Setpoints and thresholds
- Display-to-thermometer agreement for the water temperature sensor: within +/- 2 degrees.
- Reference for the sensor check: the RWT/LWT temperature/voltage table (Table 26) in the Service section.
Questions engineers ask
Why won't the compressors start on my YORK YLAA?
The manual lists four causes in order: demand not great enough, a defective water temperature sensor, a contactor/overload failure, or a compressor failure. The first is not a fault — the compressors stay off until the demand for cooling is great enough.
Is COMPRESSOR(S) WON'T START a fault on the YLAA?
Not necessarily. The manual's first listed cause is demand not great enough, and its action for that case is that there is no problem; the remaining causes are the water temperature sensor, the contactor/overload, and the compressor.
How do I check the water temperature sensor on a YLAA?
Compare the display reading with a thermometer — the two should agree within +/- 2 degrees. Then use the RWT/LWT temperature/voltage table (Table 26) in the Service section for the sensor's expected values.
What needs replacing when the YLAA shows COMPRESSOR(S) WON'T START?
For a contactor/overload failure, the manual says to replace the defective part. For a compressor failure, diagnose the cause of the failure and replace the compressor.
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