Air Compressor Troubleshooting

Cooler fins clogged up, six or seven out of ten high temperature machines are this cause. Compressor rooms with heavy dust, lots of lint especially bad. Fin gaps packed with stuff, air can’t blow through, heat stays trapped inside. Take about 85 psi compressed air, air gun nozzle at 45 degree angle following the fin direction, blow top to bottom, push dust outward. Oil sludge stuck hard, first spray cleaner and soak ten minutes then blow. Fins cleaned up, temperature can drop 25 to 35 degrees.

Fan not turning or turning slow, touch the motor housing and you’ll know. Motor hot to the touch means it’s seized or has inter-turn short circuit. Motor temperature normal but fan not turning, check relay and contactor. Fusheng machines commonly have fan capacitor failure, swap in a 25μF capacitor and done. Ingersoll Rand VFD machines, cooling fan also VFD controlled. Inverter not giving enough frequency, fan speed can’t come up, check inverter output.

Machine room ambient temperature above 104°F, no matter how good the cooling system it can’t hold down temperature. Simple test: take all side panels off the machine and run it open, if temperature comes down, it’s machine room ventilation problem. Some plants cram two or three machines in one small room, summer they simply can’t run. Solution is add ducting on the machine exhaust side, use axial fan to pull hot air directly outside.

Can’t see oil in the sight glass, or can only see a little at the bottom, oil is low. Screw machine running, oil foams and expands. Oil level looks okay, but actual amount circulating isn’t enough. Stop machine ten minutes for oil foam to settle, oil level in middle to upper part of sight glass is normal.

Oil used too long will degrade. Color changes from golden to dark brown. Rub between fingers feels sticky and gritty, means time to change. Atlas Copco OEM oil goes 3,000 hours before change. Using domestic substitute oil, 2,000 hours is safer. Water got into oil will emulsify and turn white, this must be changed immediately.

Oil cooler plugged, oil temperature won’t come down. Test method is feel temperature difference between oil cooler inlet and outlet. Normal operation inlet is hot to touch, outlet is warm, temperature difference 35°F or more. Inlet and outlet temperature about the same, means oil cooler internals are dirty.

Thermal valve failure easy to overlook. Thermal valve’s job is when oil temp is low, let oil bypass and skip the cooler. Oil temp high, then let oil go through cooler. Valve core stuck in bypass position, oil never goes through cooler, temperature definitely high. Oil filter differential pressure above 22 psi, time to change element.

Bearing wear generating heat has a characteristic: temperature rises slowly. Not sudden high temperature alarm, but every day a couple degrees higher, after a month or two then exceeds limit. By then noise also gets louder. Put your ear against machine housing can hear abnormal humming or metal friction sound. Use vibration tester on airend bearing location. Vibration value exceeding 0.28 in/s, time to schedule major overhaul.

Screw clearance too large, during compression process high pressure gas leaks back, equals internal idling doing useless work, energy turns into heat. This situation shows as high temperature, current normal to slightly high, insufficient discharge volume all appearing together. Temperature sensor usually PT100 RTD. Signal wire contact loose or RTD itself drifting, measured reading isn’t accurate. Use infrared thermometer gun on discharge pipe surface, if more than 15°F lower than controller display, sensor has problem.

Can’t build pressure, use points can’t get supply, production line affected. This is the most urgent fault. Inlet valve not opening or not opening enough, less air going in, less coming out naturally. Pull the inlet pipe off the air filter seat, let machine load, observe inlet valve plate position. Plate should fully retract, intake passage completely open. Plate only half open or opens then closes again, check inlet valve servo cylinder, control solenoid valve, air lines for leaks.

Air filter differential pressure gauge needle in red zone, or differential value exceeds 2 inches water, time to change air filter. Open air filter housing and look at element condition. Filter paper black and oily, don’t hesitate. Dusty environments one to two months need changing. Low dust can go six months.

Minimum pressure valve stuck and not sealing, system can’t hold pressure. Test minimum pressure valve separately: block the outlet, see if machine can build pressure. Can hold pressure means valve is okay. Can’t hold, disassemble and check valve core and spring. Oil separator element damaged lets oil get into compressed air, also affects pressure.

Airend internal leakage is a more serious problem. Method to test volumetric efficiency: prepare a receiver tank of known volume, say 35 cubic feet. Connect machine discharge directly into it. Record time needed to go from 0 to 115 psi. Measured time exceeding theoretical value by 30%, airend efficiency is shot.

Turn off all air-using equipment, let machine fill tank to rated pressure then stop. Watch pressure gauge, within 15 minutes pressure shouldn’t drop more than 7 psi. Drops too fast means system has leak points. Crude method to find leaks is brush on soapy water and look for bubbles. More efficient is ultrasonic leak detector. Leaking spots emit ultrasonic signal. Wearing headphones can hear hissing sound.

Common leak locations: pipe threaded fittings with aged thread tape. Flange gaskets deformed and not sealing. Ball valve stem packing leaking. Cylinder seals worn. Pneumatic tools with accumulated wear leak heavily. Go through one production line often can find ten to twenty leak points. Fix them one by one, saves good amount of electricity every day.

Machine outlet 115 psi, by the time it reaches workshop use point only 70 psi. 45 psi difference lost on the way. Pipe resistance mainly comes from three places: pipe diameter too small, pipe too long, too many elbows and tees. Simple estimate method is every 100 feet of pipe loses 1.5 to 3 psi. Each 90 degree elbow equals 10 feet of straight pipe. Each tee equals 20 feet of straight pipe.

Pipe inner wall rust and scale, cross-section area shrinks, equivalent to pipe diameter getting smaller. Old factory carbon steel pipes used for ten or twenty years, rust layer on pipe wall several millimeters thick. Filters, oil-water separators, dryers at end points all produce pressure drop. Each stage 3 to 7 psi. Hose too thin and too long is also a problem. Take a 1/4 inch ID hose from main pipe and run fifteen feet to a pneumatic tool, pressure loss is large.