By Marcus Lindqvist · Updated August 30, 2026 · 5 min read
Short answer
The five most reliable signs of a wearing compressor are falling capacity at the same power, rising discharge temperature, changes in vibration or noise, abnormal oil pressure, consumption or analysis results, and growing leaks at the shaft seal. Each one is easiest to see as a trend against the machine's own history, which is why logging operating data matters more than any single reading.
Industrial and commercial refrigeration compressors rarely fail without warning. Screw and reciprocating machines usually show a gradual change in how they run weeks or months before something breaks. The difficulty is that each sign is small on its own and easy to explain away. Below are the five that matter most, what usually causes them and what to check.
1. Is the compressor delivering less capacity for the same power?
Wear opens internal clearances. In a reciprocating compressor, leaking suction or discharge valves and worn piston rings let gas slip back. In a screw compressor, worn bearings let the rotors move, and leakage across the rotor tips and ends increases. Either way, the machine moves less refrigerant per revolution.
You will typically see:
- longer run times or more compressors online to hold the same room or leaving-water temperature;
- higher motor amps or kW for the same suction and condensing conditions;
- on a screw, the slide valve sitting further toward full load than it used to at similar loads.
The fair comparison is against logged data at similar suction pressure, condensing pressure and load. A plant that records these values every shift will spot the drift; a plant that does not will only notice when it cannot hold temperature on a hot day.
2. Is the discharge temperature rising?
Discharge temperature is one of the most sensitive health indicators. Gas that leaks back internally is compressed again, picks up more heat and raises the discharge temperature. Broken or leaking valves in a reciprocating compressor are a classic cause. On a screw, rising discharge temperature may point to a problem with oil injection, the oil cooler or liquid injection, rather than wear itself.
Not every rise means wear. High condensing pressure, high suction superheat and a low refrigerant charge also push discharge temperature up. That is why the reading has to be compared with suction and condensing conditions at the same time. Ammonia runs much hotter on discharge than HFCs at the same pressure ratio, so the alarm settings and the normal range are specific to the refrigerant and the machine.
3. Has the vibration or noise changed?
Bearings, rotors and drive couplings all have characteristic vibration signatures. As a rolling-element bearing wears, defect frequencies appear in the vibration spectrum, often long before the noise is audible. Misalignment between the motor and an open-drive compressor shows up at multiples of running speed and accelerates bearing and shaft seal wear.
In reciprocating compressors, new knocking can mean worn connecting-rod or main bearings, or loose parts. It can also mean liquid refrigerant entering the cylinders, which is a system problem that destroys valves and rods quickly.
Useful checks include periodic vibration readings at the same points with the same equipment, spectrum analysis when the overall level changes, and coupling alignment after any motor or compressor work.
4. Is the oil telling you something?
Oil problems show up in several ways:
- Oil pressure. On a reciprocating compressor with a pump, falling net oil pressure can indicate worn bearings or a worn pump. On a screw, a rising pressure drop across the oil filter means the filter is collecting debris, which itself has a source.
- Oil consumption. Needing to add oil more often points to carryover from a degraded separator or, on reciprocating machines, worn rings.
- Oil analysis. Rising iron, copper or tin, a worse ISO 4406 particle code, water or a climbing acid number all point to wear or contamination inside the machine.
See our article on what oil analysis tells you for how to read those results.
5. Is the shaft seal leaking more?
Open-drive compressors, which include almost all ammonia machines, have a mechanical shaft seal. A small amount of oil seepage is normal by design, and manufacturers state what they consider acceptable. A steady increase in oil drip, the smell of ammonia near the seal, or HFC traces found with a leak detector are signs that the seal faces or the bearings behind them are wearing.
Seal leaks also carry regulatory weight. On HFC equipment, EPA leak repair rules under the AIM Act apply to appliances holding 15 lb or more of an HFC or substitute refrigerant with a GWP above 53, effective January 1, 2026. On ammonia plants with 10,000 lb or more, OSHA’s Process Safety Management standard (29 CFR 1910.119) requires mechanical integrity programs that cover this kind of equipment.
How do the signs map to likely causes?
| Symptom | Likely cause | What to check |
|---|---|---|
| Lower capacity, higher kW per ton | Valve or ring wear (recip), bearing wear and rotor leakage (screw) | Logged amps and pressures vs. history; slide valve position; end float on screws |
| High discharge temperature | Internal leakage, valve damage, oil injection or cooling problem | Discharge temp vs. suction and condensing conditions; oil cooler; liquid injection |
| New vibration or noise | Bearing wear, misalignment, loose parts, liquid floodback | Vibration spectrum, coupling alignment, suction superheat |
| Oil pressure or consumption changes | Bearing or pump wear, separator problem, ring wear | Net oil pressure, filter pressure drop, oil analysis |
| Increasing shaft seal leakage | Seal face wear, bearing play, misalignment | Seal drip rate, leak detection, shaft end play |
Why do these signs matter more together?
One sign alone may have an innocent explanation. Two or three appearing together, for example higher discharge temperature, more iron in the oil and a new frequency in the vibration spectrum, rarely do. The practical approach is to keep a simple log: daily operating pressures and temperatures, motor current, slide valve position, oil added, and periodic vibration and oil analysis results. Trends in that log are what turn a surprise breakdown into a planned overhaul.
Our team in Ukraine works this way on screw compressors in food processing and on refrigeration systems for a national grocery chain. If you maintain compressors in Central Texas and keep logs like these, we would like to meet you. See our open positions or partnership options.
What should you do after spotting the signs?
Start with documentation. Record the date, readings and what changed, and compare them against the log sheet approach so the trend is visible. Confirm the compressor identity from its plate with how to read a compressor nameplate, because model and refrigerant decide which limits apply.
Then separate cause from symptom. Repeated high discharge temperature or oil carryover may point to upstream problems; common compressor failure causes lists what to check. If a failure has already happened, compressor burnout causes and symptoms explains what to preserve. Planning ahead is cheaper than reacting, and rebuild vs. replace gives a framework for the decision.
Frequently asked questions
How long does an industrial refrigeration compressor last?
There is no fixed number. Manufacturers specify inspection and overhaul intervals in run hours, and the actual life depends on operating conditions, oil cleanliness and how well the machine is protected from liquid. Well-maintained screw compressors are commonly overhauled rather than replaced.
Is a noisy compressor always a worn compressor?
No. Noise can come from liquid floodback, loose mounts, piping resonance or a drive problem. A change in noise is a reason to measure vibration and check operating conditions, not a diagnosis on its own.
What is the most useful single measurement to log?
If you can only log one thing, log discharge temperature together with suction and condensing pressure. Those three values reveal internal leakage, cooling problems and system issues. Motor current is a close second.
