On a York YK chiller with an OptiView control center, "Evaporator – Low Pressure" is a safety shutdown. York form 160.54-O1 says it means the evaporator pressure, as sensed by the evaporator transducer, has dropped to the safety shutdown threshold. For water cooling with R-134a, that manual lists the threshold as 25.0 psig, with restart allowed at 25.1 psig once the Compressor Switch is placed in Stop-Reset (O).
What does the Evaporator – Low Pressure message mean?
York's OptiView operation manual for YK chillers through Style G, form 160.54-O1 (issue date 11/19/2021), lists "Evaporator – Low Pressure" under safety shutdown messages. The control reads the evaporator pressure from the evaporator transducer. When that reading falls to the safety shutdown threshold, the chiller stops. For water cooling, the manual says the threshold is a fixed value for the refrigerant. For brine cooling, it varies with the concentration of the brine solution and is programmed at the York factory.
| Application and refrigerant | Shutdown (psig) | Restart (psig) |
|---|---|---|
| Water cooling, R-22 | 54.3 | 54.4 |
| Water cooling, R-134a | 25.0 | 25.1 |
| Brine cooling, R-22 | 25.0 to 54.3, as programmed | 0.1 above the shutdown threshold |
| Brine cooling, R-134a | 6.0 to 25.0, as programmed | 0.1 above the shutdown threshold |
The manual says the brine threshold should not be changed by anyone other than a qualified service technician following the OptiView service instructions, form 160.54-M1.
The same manual's pressure temperature chart (Table 2) describes the water-duty low evaporator pressure cutout as adjustable from 25 to 30 psig when Smart Freeze is disabled. It trips when evaporator pressure is at or below the cutout for 0.5 seconds. For brine duty it lists adjustable ranges of 6 to 30 psig for R-134a, 8.8 to 34.4 psig for R-513A and 0.4 to 18.4 psig for R-1234ze. The message description and the chart give different pictures of the water-duty value, so read the cutout programmed on your panel rather than assuming 25.0 psig.
Is there a warning before the shutdown?
Yes. Form 160.54-O1 lists a "Warning – Evaporator – Low Pressure Limit" message. It appears when evaporator pressure drops to the warning threshold. While it is active, the pre-rotation vanes are inhibited from opening further. The message clears by itself, and the vanes may open again, when pressure rises to the reset value.
| Refrigerant | Warning, water (psig) | Reset, water (psig) | Warning, brine | Reset, brine |
|---|---|---|---|---|
| R-22 | 56.2 | 57.5 | 1.9 above the safety setpoint | 3.2 above the safety setpoint |
| R-134a | 27.0 | 28.0 | 2.0 above the safety setpoint | 3.0 above the safety setpoint |
If the history shows this warning before the shutdown, the pressure fell gradually. That fits a process cause better than a sudden sensor failure. This is our reading, not York's.
Which messages are easy to confuse with it?
Form 160.54-O1 has several evaporator and flow messages that sit close to this one. Read the exact wording before you pick a procedure.
| Message | What 160.54-O1 says |
|---|---|
| Evaporator – Low Pressure – Smart Freeze | Smart Freeze shut the chiller down because the evaporator refrigerant temperature stayed below the freeze threshold longer than allowed. The threshold is 32.8°F when sensor RT7 is enabled and 34.0°F when it is not. Smart Freeze is active only if a service technician has enabled it and the leaving chilled liquid setpoint is below 38.0°F. |
| Evaporator – Transducer Or Leaving Liquid Probe | The control converts evaporator pressure to a saturated temperature and compares it with the leaving chilled liquid temperature. If the difference stays outside –2.5°F to +25.0°F continuously for 10 minutes, the chiller shuts down. The manual calls this a possible defective evaporator pressure transducer or leaving chilled liquid temperature transmitter. |
| Evaporator – Transducer Or Temperature Sensor | The saturated temperature from the evaporator pressure differs from the optional evaporator refrigerant temperature sensor by more than 3.0°F continuously for 1 minute. |
| Leaving Chilled Liquid – Flow Switch Open | A cycling shutdown, not a safety. The chilled liquid flow switch stayed open for 5 continuous seconds while running (2 seconds with software C.OPT.01.15A.xxx and earlier), or did not close during system prelube. The chiller restarts automatically when the switch closes. |
What does York say to check for low suction pressure?
We did not find a cause list for this message in 160.54-O1; the manual says advanced diagnostics and troubleshooting information are in the service instructions, form 160.54-M1. York's YK Style H operation and maintenance manual, form 160.76-O1, has an operation analysis chart (Table 3) with a symptom of abnormally low suction pressure. That manual is written for Style H, so treat it as a checklist for older styles, not a style-specific procedure.
| What you see | Possible cause | Remedy (160.76-O1) |
|---|---|---|
| Leaving chilled water to evaporator refrigerant temperature difference greater than normal, with high discharge temperature | Insufficient refrigerant charge | Check for leaks and charge refrigerant into the system |
| Same, with high discharge temperature | Variable orifice problem | Remove obstruction |
| Same temperature difference, with normal discharge temperature | Evaporator tubes dirty or restricted | Clean evaporator tubes |
| Chilled water temperature too low, with low motor amperes | Insufficient load for system capacity | Check pre-rotation vane motor operation and the low water temperature cutout setting |
Check the reading before you replace the transducer
The shutdown acts on the transducer's reading, so a reading that is wrong produces the same message as a real low pressure. Form 160.54-O1 lists the valid evaporator pressure range for R-134a, R-513A and R-1234ze as 5.5 to 77.4 psig. Our practical advice:
- Record the message and history. Note whether the low pressure warning came first and what the evaporator pressure and leaving chilled liquid temperature were.
- Compare the panel with a gauge. Put a calibrated gauge on the evaporator at the same time the panel shows its reading. If they agree, the low pressure is real and the causes in the table above apply.
- Compare pressure with temperature. If the saturated temperature and leaving chilled liquid temperature disagree badly, the panel's own plausibility check may already be pointing at the transducer or the leaving liquid sensor.
- Check chilled water flow. Reduced flow and low load both appear in York's lists. Confirm pumps, strainers and the flow switch circuit.
- Replace only what the checks point to. Match the part number on the old transducer or sensor.
Parts involved
| Component | Role in this issue | Where to find it |
|---|---|---|
| Evaporator pressure transducer | The input this shutdown acts on. Evaporator transducers are listed by part number; match the number on yours. | York 025-28678-112 Transducer, Pressure, Evaporator | OEM Chiller Part |
| Evaporator pressure transducer | A second evaporator transducer listing with a different part number. Our listing's fit data names Style H and later YK models, which this article's message values do not cover, so match the number on your old part. | York 025-28678-115 Transducer, Pressure (Evaporator) | OEM Chiller Part |
| Leaving chilled liquid sensor | Named with the transducer in the "Transducer Or Leaving Liquid Probe" message. Send us the sensor's part number and your nameplate and we will match it. | York Chiller Sensors, Thermistors & Transducers |
| Chilled liquid flow device | A flow sensor listing. Confirm it is the flow device on your chiller before ordering. | York 025-41573-000 Sensor, Flow 1/2" NPT | OEM Chiller Part |
Scope: Message meanings and thresholds come from York form 160.54-O1, the OptiView control center operation manual for YK chillers through Style G (issue date 11/19/2021). The troubleshooting chart comes from form 160.76-O1, the YK Style H operation and maintenance manual. YK Style H and J panels have their own OptiView manual, 160.76-O2, which we did not use. The products above are examples listed by live title, not a fit confirmation for your chiller.
Before you order
Confirm your chiller's model, style and serial number from its nameplate, and read the part number off the old transducer or sensor. For the full set of OptiView message families, see York Chiller Fault Codes: What OptiView Shutdown Messages Mean, or browse York YK Centrifugal Chiller Parts. To confirm fit, contact us at help@totalhvacparts.com or 302-219-4994 with the model, style, serial number and the part number on the old part.
Frequently Asked Questions
What does Evaporator – Low Pressure mean on a York YK chiller?
It is an OptiView safety shutdown. York form 160.54-O1 says the evaporator pressure, as sensed by the evaporator transducer, has dropped to the safety shutdown threshold. Restart needs pressure at the restart threshold and the Compressor Switch placed in Stop-Reset.
What is the York YK low evaporator pressure cutout for R-134a?
The message description in 160.54-O1 lists 25.0 psig shutdown and 25.1 psig restart for water cooling. The same manual's Table 2 shows the water-duty cutout as adjustable from 25 to 30 psig. Check the value programmed on your panel.
Can a bad evaporator transducer cause a low pressure shutdown?
The shutdown acts on the transducer's reading, so a wrong reading can trigger it. Compare the panel reading with a calibrated gauge. York's separate "Evaporator – Transducer Or Leaving Liquid Probe" message flags a transducer and leaving liquid sensor that disagree.
What causes low suction pressure on a York centrifugal chiller?
York's YK Style H manual, 160.76-O1, lists insufficient refrigerant charge, a variable orifice problem, dirty or restricted evaporator tubes and insufficient load for system capacity, each with its remedy.
Sources
- York form 160.54-O1, OptiView Control Center operation manual, YK through Style G (Section 3 display messages: safety shutdown, warning and cycling messages; Table 1 analog input ranges; Table 2 pressure temperature chart)
- York form 160.76-O1, YK Style H operation and maintenance (Table 3, operation analysis chart: abnormally low suction pressure)
- Live product titles for the parts listed above, as shown on each product page
York centrifugal chillers involve line voltage, control circuits, refrigerant under pressure and rotating equipment. Service should be performed only by qualified personnel, following York's documentation for your chiller and your facility's lockout/tagout procedures.