Troubleshooting Screw Compressors

Systematic diagnosis saves time and prevents unnecessary parts replacement. This guide covers common problems and their solutions.

Diagnostic Approach

The 5-Step Method

Define the problem - What exactly is happening?
Gather data - Pressures, temperatures, hours, history
Isolate the cause - Systematic elimination
Correct the problem - Address root cause, not just symptoms
Verify the fix - Confirm normal operation

Key Operating Parameters

Parameter	Normal Range	Measure At
Discharge pressure	Per design ±5%	Separator tank
Discharge temperature	160-200°F (70-95°C)	Discharge port
Oil temperature	140-180°F (60-82°C)	Oil sump/separator
Oil pressure	15-30 PSI above discharge	Before filter
Inlet pressure	-0.5 to -2 PSI vacuum	Inlet filter
Motor amps	Per nameplate ±10%	All phases

Common Problems and Solutions

1. Compressor Won't Start

Troubleshooting flowchart:

    Won't Start
         │
    ┌────┴────┐
    │ Power?  │
    └────┬────┘
      No │ Yes
      ↓  │
   Check ├──────────────┐
   supply│              │
         │         ┌────┴────┐
         │         │ Control │
         │         │ power?  │
         │         └────┬────┘
         │           No │ Yes
         │           ↓  │
         │        Check ├─────────────┐
         │        fuses │             │
         │              │        ┌────┴────┐
         │              │        │ Safety  │
         │              │        │ lockout?│
         │              │        └────┬────┘
         │              │          Yes│ No
         │              │           ↓ │
         │              │        Check├────→ Motor/
         │              │        fault│      starter
         │              │        codes│      issue

Symptom	Possible Cause	Solution
No power indication	Main breaker tripped	Reset, check for shorts
Control power, no start	E-stop engaged	Release and reset
	High temperature lockout	Cool down, check cooler
	Low oil level	Add oil, check for leaks
	Pressure switch fault	Check settings, replace if failed
Motor hums, won't turn	Single-phasing	Check all phases
	Seized compressor	Check manually, may need rebuild

2. Low Discharge Pressure

System pressure low
         │
    ┌────┴────┐
    │ Demand  │
    │ changed?│
    └────┬────┘
      Yes│ No
       ↓ │
   Normal├──────────────┐
   if load│             │
   increased│      ┌────┴────┐
         │        │ Inlet   │
         │        │ filter  │
         │        │ ΔP?     │
         │        └────┬────┘
         │        High │ Normal
         │          ↓  │
         │       Replace├────→ Check
         │       filter │      internal
         │              │      issues

Symptom	Possible Cause	Solution
Gradual decline	Inlet filter clogged	Replace element
	Leaks in system	Leak survey and repair
	Worn intake valve	Inspect/replace valve
	Capacity control fault	Check modulation valve
Sudden drop	Demand increase	Add capacity
	Major leak	Emergency leak check
	Pressure switch failure	Replace switch
	Relief valve opening	Check setting, look for cause

3. High Discharge Temperature

Normal: 160-200°F (70-95°C) above ambient + compression heat

High Temperature

Temperatures above 225°F (107°C) cause oil breakdown and accelerated wear. Above 250°F (121°C) requires immediate shutdown.

Cause	Indicators	Solution
Cooler fouled	High temp, normal airflow	Clean cooler fins
Low airflow	High temp, fan running	Check fan, clear obstructions
Fan failure	High temp, fan not running	Replace fan motor/belt
Low oil level	High temp, low sight glass	Add oil, check for leaks
Wrong oil	Recent oil change	Drain and refill correct oil
Thermal valve stuck	Oil bypasses cooler	Replace thermal valve
High ambient	Temp rises with room temp	Improve ventilation
Oversized at low load	Hot at low demand	Adjust cycling or load

Oil flow through thermal valve:

COLD OIL:                    HOT OIL:
(Bypass cooler)              (Through cooler)

    ┌──────────┐                ┌──────────┐
    │ Thermal  │                │ Thermal  │
────│ ●  Open  │────→           │ ●  Closed│
    │ to sump  │            ────│          │────→
    └─────┬────┘                └─────┬────┘
          │                           │
          ╳ Closed                    ↓
          │                      ┌────────┐
      To Cooler                  │ Cooler │
                                 └────────┘

4. High Oil Consumption

Normal consumption: 1-2 pints per 1,000 hours

Symptom	Cause	Solution
Oil in discharge air	Separator element failed	Replace element
	Overfilled oil sump	Drain to correct level
	Scavenge line clogged	Clean or replace line
	Wrong oil viscosity	Use correct oil
Oil leaks visible	Gasket/seal failure	Replace gaskets/seals
	Loose fittings	Tighten connections
Rapid level drop	Separator failure	Inspect and replace
	Internal leak to air side	Rebuild compressor

Scavenge line function:

                    Separator Tank
                    ┌────────────────┐
                    │    ░░░░░░░░    │ ← Separator element
                    │    ░░░░░░░░    │
                    │ ┌──┴──┐        │
    Clean air out ←─┼─┤     │        │
                    │ └──┬──┘        │
                    │    │  Scavenge │
                    │    │  line ────┼──→ Returns oil
                    │    │           │    to airend
                    │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ ← Oil level
                    └────────────────┘

5. Excessive Noise/Vibration

Sound	Likely Cause	Action
Metallic rattling	Loose components	Inspect, tighten
Grinding	Bearing failure	Immediate shutdown, repair
Knocking	Liquid ingestion	Check inlet, dryer, traps
Squealing	Belt slipping	Adjust/replace belts
Pulsation	Inlet valve issue	Inspect/repair valve
High-pitched whine	Gear or bearing wear	Schedule rebuild

Vibration analysis reference:

Frequency	Typical Cause
1x RPM	Imbalance, misalignment
2x RPM	Misalignment, looseness
High frequency	Bearing defects
Random	Cavitation, turbulence

6. Oil in Compressed Air

Beyond separator carryover limit (typically 2-3 ppm):

Cause	Diagnosis	Solution
Separator element failure	Visual inspection, high carryover	Replace element
Minimum pressure valve stuck	Low tank pressure at unload	Repair/replace valve
Overfilled oil	Level above maximum mark	Drain to correct level
Oil foaming	Emulsified appearance	Check for water, change oil
Wrong separator	Check part number	Install correct element
Scavenge system fault	Oil pooling in separator	Clear scavenge line

7. Water in Oil

Symptoms: Milky oil appearance, emulsion

Cause	Solution
Aftercooler leak	Pressure test, repair
Operating below dew point	Increase load or temperature
Condensation during shutdown	Install crankcase heater
Coolant leak (water-cooled)	Pressure test heat exchanger

8. Frequent Loading/Unloading (Short Cycling)

Normal cycle time: >30 seconds loaded, >30 seconds unloaded

Cause	Solution
Pressure band too narrow	Widen load/unload differential
Tank too small	Add receiver capacity
Large intermittent demand	Add point-of-use storage
Leak in control air	Check and repair
Faulty pressure transducer	Calibrate or replace

After Oil Change

Problem	Cause	Solution
High temperature	Wrong oil type	Drain, flush, correct oil
Foaming	Incompatible oils mixed	Complete drain and flush
Low pressure	Overfilled	Drain to correct level
Oil leaks	Disturbed seals	Re-torque, replace seals

After Filter Change

Problem	Cause	Solution
High ΔP	Wrong element	Verify part number
Bypass alarm	Element not seated	Reinstall properly
Oil carryover	Separator installed wrong	Check orientation

After Major Service

Problem	Cause	Solution
Won't build pressure	Minimum pressure valve stuck	Free or replace
High temperature	Air in oil system	Run to purge air
Vibration	Components not torqued	Re-torque to spec

Diagnostic Tools

Tool	Use
Infrared thermometer	Temperature spot checks
Ultrasonic detector	Leak detection, bearing analysis
Clamp ammeter	Motor current verification
Pressure gauges	System pressure checks
Oil analysis kit	Sample collection for lab
Vibration pen	Quick vibration screening

When to Call for Service

Unusual metallic sounds
Smoke or burning smell
Oil spraying
Temperature won't stabilize below limit
Vibration suddenly increases
Motor trips repeatedly
Any safety system activation

Documentation

Keep a log of operating parameters. Trends are more valuable than single readings for predicting problems.

Diagnostic Approach​

The 5-Step Method​

Key Operating Parameters​

Common Problems and Solutions​

1. Compressor Won't Start​

2. Low Discharge Pressure​

3. High Discharge Temperature​

4. High Oil Consumption​

5. Excessive Noise/Vibration​

6. Oil in Compressed Air​

7. Water in Oil​

8. Frequent Loading/Unloading (Short Cycling)​

Maintenance-Related Issues​

After Oil Change​

After Filter Change​

After Major Service​

Diagnostic Tools​

When to Call for Service​