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Industrial Air Cooler<\/a> Hey everyone, it\u2019s Jake here from the screw chiller crew, and I\u2019ve spent the last 8 years helping facility managers, industrial ops teams, and small business owners fix chillers that won\u2019t stop throwing fits. Let\u2019s cut to the chase: your screw chiller\u2019s sensors are lying to you\u2026 sometimes. Not on purpose, but if you\u2019re just staring at the dash readings and hitting reset when a fault pops, you\u2019re missing the stuff that stops breakdowns before they shut down your production line or freezer warehouse. This post is the straight talk version of how I actually analyze that sensor data\u2014not some textbook fluff you can\u2019t apply on a Tuesday afternoon when your shift\u2019s about to end. First off, let\u2019s get one thing straight: I don\u2019t care about fancy jargon. I care about real problems: sudden ice buildup on evaporators, sky-high power bills, weird pressure spikes that make your tech call me at 2 a.m. These tips work for every screw chiller sensor, and they\u2019re the exact moves we use when a client\u2019s chiller is acting weird and they need answers fast. Let\u2019s start with the biggest mistake I see most people make: they look at individual sensor readings like they\u2019re single pieces of a puzzle, not the whole scene. I\u2019ve seen a client\u2019s chiller show a \u201chigh discharge temp\u201d fault, so they swapped the discharge temp sensor\u2026 and the next week, the compressor died. Turned out the water flow sensor was clogged, so refrigerant wasn\u2019t absorbing heat, making the discharge temp rise, which the sensor caught. But because they only fixed the sensor, not the root cause, the compressor burned out. Moral of that story: never trust one sensor. Always cross-reference at least 2-3 related ones. Here\u2019s how we break that down step by step, no acronym overload (but if I use one, I\u2019ll explain it like I\u2019m talking to a buddy who knows chillers a little). First, let\u2019s list the main sensors your screw chiller\u2019s got because you can\u2019t analyze data if you don\u2019t know what you\u2019re looking at: 1. Suction and discharge pressure sensors (they measure the pressure going into and out of the compressor\u2014think of this like your car\u2019s oil pressure, but for refrigerant). 2. Suction and discharge temp sensors (the temps at those same pressure points). 3. Entering and leaving water temp sensors (the water going into your chiller from the building and going back out to cool it\u2014super important for HVAC chillers). 4. Oil pressure and oil temp sensors (screw chillers use oil to lubricate the rotors, so this is make-or-break for the compressor). 5. Current sensor (measures how much power the compressor\u2019s pulling\u2014this tells you if it\u2019s working too hard). Now, step one: pull the baseline data first. If your chiller\u2019s been running for a month with no issues, write down what the sensors read at the exact load it\u2019s running at. Let\u2019s say a food processing plant runs their chiller at 75% load 24\/7\u2014their baseline would be suction pressure at 85 psi, discharge at 210 psi, leaving water at 45\u00b0F. If next week, suction pressure drops to 72 psi at the same 75% load, that\u2019s a red flag. No, it\u2019s not a \u201csensor error\u201d until you check it against something else. Now, step two: check for sensor drift first, before blaming the whole chiller. This is the #1 thing I troubleshoot in the first 10 minutes of a call. Sensors don\u2019t just go bad suddenly\u2014they drift over time, usually because of dirt, vibration, or just age. How do you test that? Grab two identical sensors (or a portable pressure\/temp meter that we carry, since we\u2019re chillers guys) and tap it next to the installed sensor. If the installed suction pressure sensor says 85 psi and the portable says 79 psi? That drift\u2019s got to go, and fast. I had a bakery client once whose chiller was blowing warm bread cooling air, and they were blaming the compressor. We checked their leaving water sensor\u2014it read 50\u00b0F, but the portable said 42\u00b0F. Turned out the sensor was coated in dust from flour, so it was reading way higher than actual. Swapped the sensor, problem fixed, no compressor replacement needed. Sensor drift is easy to mix up with actual chiller issues, so always rule that out first\u2014don\u2019t waste time pulling the compressor apart over a bad $50 sensor. Step three: cross-reference pressure and temp pairs, because screw chillers run on refrigerant pressure-temp curves, that\u2019s non-negotiable. Refrigerants (we use R-134a most now, but R-410A too) have a fixed rule: for any given pressure, there\u2019s only one saturation temp (that\u2019s the temp where the refrigerant turns from liquid to gas, or vice versa). So here\u2019s the math, no calculator app needed. If the suction pressure sensor says 80 psi for R-134a, the saturation temp should be around 40\u00b0F. If your suction temp sensor reads 48\u00b0F? That\u2019s a sign you\u2019ve got \u201csuperheat\u201d issues, which means the refrigerant line has too much gas and not enough liquid, or there\u2019s air in the system. I\u2019ve seen this cause a chiller to use 20% more power than normal, because it\u2019s working extra hard to cool the building. Conversely, if discharge pressure is 200 psi, saturation temp should be around 105\u00b0F. If your discharge temp is 115\u00b0F? That means the compressor is working too hard, usually because of dirty condenser coils or low refrigerant charge. This is way more reliable than just staring at the discharge temp reading alone, because it ties two sensors together. Step four: watch for trends, not one-off spikes. Sensor faults aren\u2019t just random 1-minute blips\u2014those are usually just electrical glitches. A real problem is when a sensor stays off for 3 hours straight, or trends in a weird direction over a week. For example, I had a pharmaceutical client who kept getting \u201clow suction pressure\u201d alarms. First, we checked the sensor, it was fine. Then we looked at the trend over a month: suction pressure was dropping 5 psi every week. That meant refrigerant was slowly leaking out, not a clog or flow issue. If we\u2019d just fixed the alarm when it popped, we would\u2019ve missed the leak, and eventually the chiller would\u2019ve had no refrigerant, destroying the compressor. Another trend thing: power draw. The current sensor on the compressor\u2014if it\u2019s spiking by 10% during the same load, that\u2019s not normal. Last year, a manufacturing plant\u2019s chiller current slowly went up over a month, and we found the evaporator tubes were scaled with mineral buildup from their water supply. The chiller was working harder to cool the water, so power draw went up, and eventually the tubes were so blocked the chiller couldn\u2019t keep up. By catching the trend in current and cross-referencing it with the leaving water temp (which was slowly rising too), we flushed the tubes and saved them $15k in compressor replacement. Step five: don\u2019t ignore the weird small sensors, like oil pressure and oil temp. Screw chillers rely on oil to seal the rotors and keep them from grinding together, so oil sensor data is like the chiller\u2019s vital signs. If oil pressure drops while the compressor is running at full load, that\u2019s not a \u201cminor alert\u201d\u2014that means the oil pump\u2019s failing, or the oil filter\u2019s clogged. I had a client who thought their oil sensor was lying because the temp was 10\u00b0F higher than normal, until we checked the oil filter and it was completely caked with metal shavings from worn rotors. If we\u2019d waited for the compressor to lock up, they would\u2019ve had a $50k repair instead of a $200 filter change. Now, let\u2019s talk about the mistakes I see people make all the time, because even if you know the steps, you\u2019ll slip up here. First: ignoring water flow. The entering and leaving water sensors don\u2019t just measure temp\u2014if the difference between entering and leaving water is less than 5\u00b0F, that means there\u2019s not enough water flow through the chiller. Too much and it can cause water hammer, but too little means your chiller is overheating. I had a grocery store once where their leaving water temp was normal, but the delta (difference) was only 2\u00b0F. Turned out the water pump was dying, so not enough water was moving through the evaporator. If we\u2019d only fixed the temp sensor, we would\u2019ve missed that, and the chiller would\u2019ve seized. Second: assuming all sensors are calibrated the same. Even two suction pressure sensors from the same brand can read 3 psi different if they\u2019re installed wrong or exposed to different temps. Always cross-check with the portable meter, like I said before, because no installed sensor is perfect forever. Third: forgetting to account for ambient conditions. If it\u2019s 95\u00b0F outside, your condenser pressure will naturally be higher than when it\u2019s 70\u00b0F. If you don\u2019t note the ambient temp, you\u2019ll think the chiller is broken when it\u2019s just the weather. Our baseline data should also include ambient temp, so you can adjust for that. Now, here\u2019s what we do when a client sends us sensor data and they\u2019re stuck\u2014we don\u2019t give them a textbook answer, we give them a fix. For example, if a client sends us: Suction pressure: 75 psi, suction temp: 45\u00b0F, discharge pressure: 195 psi, discharge temp: 110\u00b0F, leaving water: 48\u00b0F, current draw: 12% higher than baseline. First step: check if suction pressure matches the saturation temp for R-134a. 75 psi should be ~35\u00b0F, but suction temp is 45\u00b0F\u2014that\u2019s superheat. So either the refrigerant has air, or the expansion valve is stuck open. Then, current draw is high, which matches the discharge pressure being a little high (195 psi should be ~100\u00b0F, it\u2019s 110\u00b0F, so compressor is working hard). So the root cause is probably dirty condenser coils or a refrigerant charge issue. From there, we tell them to clean the condenser first, then check the refrigerant charge. No need to pull the compressor apart, no need to replace sensors. That\u2019s the stuff we live for. Now, let\u2019s wrap this up because I know you\u2019re busy\u2014these are the 5 quick checks you can do today without calling a tech: 1. Pull last week\u2019s baseline data for your chiller at its most common load. 2. Grab your portable pressure\/temp meter, check 2 sensors at random to rule out drift. 3. For each pressure, calculate the expected saturation temp for your refrigerant (Google has a quick chart, no need to memorize it) and compare to the actual temp reading. 4. Check if the leaving water delta is between 5-8\u00b0F\u2014if it\u2019s lower, check water flow; if higher, check for a refrigerant leak. 5. Look at the trend of current draw and discharge temp over the last 3 days\u2014if they\u2019re slowly going up, that\u2019s a problem, not a blip. And a quick note for our regular folks: if you\u2019re running a chiller that\u2019s 10+ years old, those sensors are going to drift more, so calibrate them every 6 months, not once a year. We\u2019ve got a cheap portable calibration tool we recommend, it saves so much hassle. At the end of the day, analyzing screw chiller sensor data isn\u2019t about being an engineer\u2014it\u2019s about connecting the dots. It\u2019s about realizing that a weird pressure reading and a slightly higher current draw aren\u2019t separate issues, they\u2019re two parts of the same problem. I\u2019ve seen too many companies waste money on unnecessary parts and repairs because they only look at one sensor, or ignore trends, or blame the sensor first before checking the actual chiller. If you\u2019re staring at your sensor data and not sure what it means, or you\u2019ve got a chiller that\u2019s throwing fault codes and you can\u2019t figure out why, reach out to our team. We work with all types of industrial, commercial, and even small-scale chillers, and we can help you parse that data, figure out the root cause, and fix it before it becomes a big, expensive problem. Don\u2019t wait for a 2 a.m. call that costs you thousands\u2014address those sensor trends now. Thanks for reading, drop a note in the comments if you\u2019ve got a chiller sensor story (good or bad), we love hearing from you. Kunshan Aotianxin Machinery Co., Ltd.<\/a>
\nReferences: Stoecker, W. F., & Jones, J. W. (1982). Refrigeration and Air Conditioning. McGraw-Hill; ASHRAE. (2021). ASHRAE Handbook: HVAC Systems and Equipment. American Society of Heating, Refrigerating and Air-Conditioning Engineers; Dossat, R. J. (1997). Principles of Refrigeration. Prentice Hall. Screw Chillers<\/a><\/p>\n![](\"https:\/\/www.atxks.com\/uploads\/47917\/small\/heavy-duty-industrial-cooler0032f.png\")
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