Master Troubleshooting Guide

System-by-system reference for rotary screw + reciprocating compressors

How to use this guide

Start with the First-response checklist below, then jump to the system most likely involved. Each system links into the symptom-driven flows under /diagnose for cause-by-cause walkthroughs.

Start here

First-response checklist

1. Make it safe

LOTO, post warning tags, drain pressure to 0 PSI at a gauge.

2. Read the controller

Capture every active alarm + recent fault history before clearing anything.

3. Walk the machine

Look, listen, smell. Oil under the unit? Burnt insulation? Hot bearings?

4. Confirm the symptom

Reproduce: does it trip on start, trip after N minutes, or run but make no pressure?

5. Isolate the system

Use this guide's system sections (electrical → pressure → temp → controls → lube → air quality → mechanical) to narrow scope.

6. One change at a time

Document each measurement and adjustment. Reversing changes is impossible if you made five at once.

7. Restore protections

Reset overloads, re-enable interlocks, replace covers and guards before energizing.

Non-negotiable

Safety rules

Lockout / tagout (LOTO) every electrical or rotating-component task. Verify zero energy before touching anything.
Bleed system pressure to 0 PSI at a gauge before opening any pneumatic joint. Stored air can launch fittings.
Drain receivers regularly — corroded tanks have failed catastrophically.
Never bypass a safety interlock (E-stop, high-temp, low-oil-pressure, door switch) to keep a machine running.
Discharge motor windings to ground after meggering; capacitive voltage can bite.
Never megger a VSD-fed motor with the drive connected — IGBTs will be destroyed.
Verify the ASME-stamped safety relief is the correct setpoint and never plug or replace with a higher one.
Hot oil from a screw separator can be > 200°F. Let it cool, wear PPE, and open the fill cap slowly.
Confirm rotation arrow on every new install and after any phase-related work — a backwards screw airend will be destroyed in seconds.

System ELECTRICAL

1 · Electrical & motor

Power supply, starters, contactors, overloads, VSDs, and motor windings. The single largest source of unplanned downtime.

Compressor will not start

Won't run · 10 causes

Trips breaker or overload

Electrical · 10 causes

Wye-Delta starter problem

Electrical · 6 causes

Contactor chattering or burning

Electrical · 5 causes

VSD (variable speed drive) fault

Electrical · 6 causes

System PRESSURE

2 · Pressure & capacity

Build-up, hold, short cycling, relief valves, and demand vs supply balance.

Low discharge pressure / won't build pressure

Pressure · 9 causes

Discharge pressure too high / safety valve lifting

Pressure · 4 causes

Short cycling (loads/unloads rapidly)

Pressure · 5 causes

Long pump-up time

Pressure · 5 causes

System TEMPERATURE

3 · Cooling & temperature

Oil/air coolers, fans, thermostatic valves, ambient considerations.

High discharge temperature

Temperature · 8 causes

System CONTROLS

4 · Controls & sensors

HMIs, PLC alarms, load/unload sequencing, transducers and RTDs.

Controller / HMI shows fault but won't clear

Controls · 4 causes

Won't transition between load and unload

Controls · 4 causes

System LUBE

5 · Lubrication

Oil pressure, viscosity, consumption, contamination — covers both sump-based screws and crankcase recips.

Low oil pressure trip (screw)

Lubrication · 5 causes

High oil consumption (reciprocating)

Lubrication · 4 causes

System AIRQ

6 · Air quality & treatment

Oil carryover, moisture, dryers, filters, condensate management.

Oil in discharge air (rotary screw)

Air quality · 6 causes

Water in discharge air

Air quality · 5 causes

Refrigerated dryer dewpoint too high

Air treatment · 5 causes

Desiccant dryer not switching towers

Air treatment · 4 causes

Automatic drain not draining

Drain / condensate · 4 causes

System MECH

7 · Drive & mechanical

Belts, sheaves, couplings, mounts, abnormal noise and vibration.

Belt squeal, slip, or premature failure

Belts / drive · 5 causes

Abnormal noise / vibration

Noise · 6 causes

Cheat sheet

Quick reference values

Electrical rules of thumb

Acceptable voltage: Nameplate ± 10% under load
Voltage imbalance: ≤ 2% phase-to-phase
Overload setting: 115–125% of motor FLA
Y-Δ heater (heater inside delta): FLA × 0.58
Coil pull-in voltage: ≥ 85% of rated
Insulation resistance (cold): ≥ 1 MΩ to ground (megger 500V/1000V)

Pressure & capacity

Receiver sizing (general): ≥ 1 gal per CFM, 4 gal/CFM for variable load
Differential band (recip): 10–20 PSI typical
Differential band (screw): 8–10 PSI typical
Acceptable leak rate: < 10% of compressor capacity
Safety relief setpoint: 10–15% above max working pressure
Recip starts/hour: ≤ 6–10 (motor-dependent)

Temperature & cooling

Screw discharge (normal): 180–200°F (82–93°C)
Screw shutdown (typ.): 220–235°F (104–113°C)
Max ambient (typical): 100–110°F (38–43°C)
Dryer inlet (max): < 100°F (38°C)
Refrigerated dryer dewpoint: 35–50°F pressure dewpoint
Each 18°F inlet rise: ≈ doubles moisture load

Filters & separators

Intake filter ΔP (replace): > 6" H₂O / 1.5 kPa
Oil filter ΔP (replace): ≈ 15–25 PSI rise vs new
Air/oil separator ΔP (replace): > 8–12 PSI
Coalescing filter (replace): > 5 PSI ΔP or annual

Belts & drive

Belt deflection: 1/64" per inch of span at 4–5 lb push
Sheave alignment: Straight-edge across faces; laser preferred
Sheave groove wear: New belt sinks below top of groove → replace
Re-tension new belts: After first 8 run-hours

Reminder

These values are general industry guidance. Always defer to the OEM manual for the specific make and model in front of you.