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Oxygen concentrators

DeVilbiss 505: troubleshooting and error codes

The ServiceForge knowledge base holds 23 documented symptoms for the DeVilbiss 505, with 85 ranked causes, 23 diagnostic checks with test points and expected values, and 0 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Fluctuating oxygen flow patient safety

Oxygen output varies during operation

Ranked causes

  1. 1. Occluded humidifier (common)
  2. 2. Improper humidifier type (occasional)
  3. 3. Occluded filters (occasional)
  4. 4. Occluded or defective patient cannula and tubing (occasional)
  5. 5. Defective flow meter (occasional)
  6. 6. System leak (occasional)
  7. 7. Defective compressor reed valve (occasional)
  8. 8. Defective check valve (occasional)
  9. 9. Pressure regulator malfunction (occasional)
First check

Check humidifier condition

Test point
Humidifier inlet and outlet ports
Expected
Clear flow path with no blockage

1 more check with pass and fail actions, 9 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Little or no oxygen flow patient safety

Minimal or zero oxygen delivery at patient outlet

Ranked causes

  1. 1. Flow meter not adjusted or disconnected (common)
  2. 2. Oxygen delivery tubing kinked or blocked (common)
  3. 3. Occluded humidifier (common)
  4. 4. Excessive tubing length (occasional)
  5. 5. Defective flow meter (occasional)
  6. 6. System leak (occasional)
  7. 7. Defective compressor or reed valve (occasional)
  8. 8. Defective check valve (occasional)
  9. 9. Pressure regulator malfunction (occasional)
First check

Verify flow meter adjustment

Test point
Flow meter dial
Expected
Set to desired flow rate (typically 5 LPM)

4 more checks with pass and fail actions, 9 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

No oxygen flow patient safety

Fan off or fan operating with no indicator lights on PC board

Ranked causes

  1. 1. Line cord not properly installed or defective (common)
  2. 2. No power at receptacle (common)
  3. 3. Oxygen concentrator circuit breaker activated (occasional)
  4. 4. Line cord quick-connect terminal disconnected (occasional)
  5. 5. Defective power switch (occasional)
  6. 6. Defective circuit breaker (occasional)
  7. 7. Blown fuse on PC board (occasional)
  8. 8. Defective PC board (occasional)

8 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Low oxygen concentration with long cycle time patient safety

Unit cycles slower than normal and oxygen concentration is low

Ranked causes

  1. 1. System leak (common)
  2. 2. Defective sieve bed check valve (occasional)
  3. 3. Defective compressor reed valve (occasional)
  4. 4. Worn compressor (occasional)
  5. 5. Occluded filters (occasional)
First check

Check for system leaks

Test point
All hoses and fittings
Expected
No bubbles when leak detection solution applied
Tools
Leak detection solution

1 more check with pass and fail actions, 5 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Unit shuts off during operation

Compressor stops, audible alarm sounds, 'Service Required' light illuminates, cooling fan continues running

Ranked causes

  1. 1. High pressure condition (common)
  2. 2. Long cycle time (worn compressor or leak) (common)
  3. 3. Short cycle time (sieve bed or four-way valve issue) (common)
  4. 4. PC board failure (occasional)
  5. 5. Uneven cycle time during operation (occasional)
First check

Measure pressure in sieve beds

Test point
Sieve bed test points at top of beds
Expected
Left bed ~26 PSI (180 kPa) pressurized, right bed ~2 PSI (15 kPa) depressurized, ±2 PSI

4 more checks with pass and fail actions, 5 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Unit warm to touch, cannot restart for several minutes caution

Compressor ran then shut off, fan operating, D17 or D17 & D18 illuminated on PC board

Ranked causes

  1. 1. Compressor overheated due to occluded filters (common)
  2. 2. Restricted input or output air passage (common)
  3. 3. Low or high line voltage (occasional)
  4. 4. Defective cooling fan (occasional)
  5. 5. Defective compressor (rare)

5 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Visible alarm on, audible alarm on, compressor off, power light off patient safety

Blinking visible alarm, pulsing audible alarm with compressor off and power light off

Ranked causes

  1. 1. Wiring harness disconnected or defective (occasional)
  2. 2. Loose compressor wire (occasional)
  3. 3. Defective capacitor (rare)
  4. 4. Defective PC board (rare)
  5. 5. Defective compressor (rare)

5 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Audible alarm does not sound when unit turned on or during power failure patient safety

No alarm tone when unit starts or loses power

Ranked causes

  1. 1. Unit unused for extended period (common)
  2. 2. Defective PC board (occasional)
  3. 3. Defective power switch (occasional)
  4. 4. Defective wire harness (occasional)

4 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Low pilot pressure

Pilot pressure system below normal operating range

Ranked causes

  1. 1. Leak in pilot pressure system (common)
  2. 2. Defective check valve in pilot accumulator (occasional)
  3. 3. Defective compressor reed valve (occasional)
  4. 4. Defective compressor (occasional)
First check

Measure pilot pressure

Test point
Pilot accumulator or pilot valve test point
Expected
22-28 PSI (150-200 kPa) during normal operation; minimum 19 PSI (130 kPa), ≥19 PSI
Tools
Pressure gauge

4 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Maximum cycle time exceeded patient safety

Compressor ran then shut off, fan operating, D17 or D17 & D18 illuminated on PC board

Ranked causes

  1. 1. Leak in system (common)
  2. 2. Defective compressor reed valve (occasional)
  3. 3. Defective compressor (occasional)
  4. 4. Four-way valve not fully shifted (occasional)

4 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Compressor will not start high voltage

Power switch in 'On' position, power indicator light on, cooling fan running, but compressor does not operate

Ranked causes

  1. 1. Defective capacitor (common)
  2. 2. Defective compressor (occasional)
  3. 3. Defective wire harness or PC board (occasional)
First check

Measure compressor supply voltage

Test point
Compressor motor terminals
Expected
115 VAC, ±10%
Tools
DMM set to AC voltage

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Excessive noise during operation caution

Unit produces abnormally loud or unusual noise levels

Ranked causes

  1. 1. Loose or defective motor mounts (common)
  2. 2. Defective compressor (occasional)
  3. 3. Defective cooling fan (occasional)
First check

Inspect motor mount fasteners

Test point
Motor mounting bolts
Expected
All bolts tight with no visible looseness
Tools
Wrench

1 more check with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Fluctuating or no flow patient safety

System pressure below 9 PSI or 62 kPa, fan operating, D16 or D16 & D18 illuminated on PC board

Ranked causes

  1. 1. Leak in system (common)
  2. 2. Defective compressor (occasional)
  3. 3. Four-way valve not fully shifted (occasional)

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Severe flow restriction patient safety

Fan operating, no indicator lights illuminated on PC board

Ranked causes

  1. 1. Crimped tubing (common)
  2. 2. Occluded humidifier (common)
  3. 3. Flow meter turned off or set too low (common)

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Four-way valve failed to shift; contaminated sieve beds patient safety

Fan operating, D17 & D16 or all three indicator lights illuminated on PC board

Ranked causes

  1. 1. Four-way valve failed to shift properly (occasional)
  2. 2. Contaminated sieve beds (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Low oxygen concentration with normal cycle times patient safety

Unit cycles normally but oxygen output is below specification

Ranked causes

  1. 1. Oxygen leak from system (common)
  2. 2. Purge valve malfunction (occasional)
First check

Inspect for oxygen leaks

Test point
Sieve bed tops, accumulator, pressure regulator, flow meter, bacteria filter, outlet port
Expected
No visible damage, no hissing sound, no bubbles when leak detection solution applied
Tools
Leak detection solution, visual inspection

2 more checks with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

OSD no lights illuminated patient safety

Oxygen Sensor Display has no illuminated indicator lights

Ranked causes

  1. 1. Connector off between OSD and PC board (common)
  2. 2. Defective OSD (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Pulsating air noise

Rhythmic or pulsing sound from unit

Ranked causes

  1. 1. Intake filter not in place or defective (common)
  2. 2. Compressor intake hose disconnected (common)
First check

Verify intake filter installed

Test point
Filter housing inlet
Expected
Filter element in place and secure

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Purge valve stuck; all diagnostic lights illuminated patient safety

Fan operating, D17 & D16 or all three indicator lights illuminated on PC board

Ranked causes

  1. 1. Purge valve stuck in activated position (occasional)
  2. 2. Defective PC board (rare)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Service Required light does not illuminate when unit is turned on

Visible alarm indicator on front panel does not light

Ranked causes

  1. 1. Defective PC board (occasional)
  2. 2. Defective light panel (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Low oxygen concentration with short cycle time patient safety

Unit cycles faster than normal and oxygen concentration is low

Ranked causes

  1. 1. Contaminated sieve beds (occasional)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

OSD both lights illuminated patient safety

Both OSD indicator lights are illuminated

Ranked causes

  1. 1. Defective OSD (unknown)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

OSD yellow low oxygen light illuminated patient safety

Yellow Low Oxygen light is illuminated with or without intermittent audible alarm every five seconds

Ranked causes

  1. 1. Oxygen level is low (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Community

0 fixes logged by technicians through their AI, with outcomes, for this model.

ServiceForge knowledge base record. Field-unverified unless technicians confirmed it. A teaching summary of the record, not a service manual. Export 2026-10-14.