20774294 | Genuine Volvo® Twin Cylinder Compressor, 636 cc

• Calculated Volume (dm³)
  18.765
• Cooling
  Water
• Crankshaft thread
  M20 x 1.5
• Lubrication
  Lubrication supplied from engine
• Max. operating pressure
  14.0 bar
• Mounting
  Flange mounting
• Operating speed
  3000 (1/min)
• Piston diameter
  85 mm
• Piston stroke
  56 mm
• Port thread 0
  Ø 34.9 mm
• Port thread 2
  M26 x 1.5
• Port thread 4
  M16 x 1.5
• Port thread 8.1
  M12 x 1.5
• Port thread 9.1
  M16 x 1.5
• Port thread 9.2
  M16 x 1.5
• Product category
  Device
• Swept volume (cm³)
  636 cm³

1. Operates the air brakes (primary purpose)

• Supplies compressed air to:

  • Service brakes

  • Parking brakes

  • Emergency brakes

• Keeps air tanks charged so brakes apply and release correctly

Why it matters:
Without air pressure, the brakes cannot function—and the system is designed to apply brakes automatically for safety.

2. Maintains safe operating air pressure

• Continuously replaces air lost during braking

• Works with the governor to regulate pressure

• Keeps pressure in the safe range (usually 120–135 PSI)

Why it matters:
Consistent pressure = predictable braking performance.

3. Powers other air-operated systems

Beyond brakes, compressed air is used for:

• Air suspension

• Clutch assist

• Air horns

• Transmission controls

• Doors and accessories

Why it matters:
One compressor supports multiple critical vehicle systems.

4. Ensures fail-safe braking

• Air brake systems are fail-safe

• If pressure drops too low, spring brakes apply automatically

Why it matters:
Prevents runaway vehicles and loss of control.

5. Supports vehicle safety and compliance

• Required by law for heavy vehicles with air brakes

• Must meet DOT air-pressure build-up standards

Why it matters:
A properly functioning compressor keeps the vehicle legal and safe to operate.

1. Slow air pressure build-up

• Takes much longer than normal to reach operating PSI

• Fails DOT air build-up test
  Cause: Worn piston rings, leaking valves, internal wear

2. Won’t reach full pressure

• Pressure stalls below ~120 PSI

• Governor never cuts out
  Cause: Internal leakage or failing compressor head

3. Air pressure drops quickly

• Pressure falls fast after braking

• Low-air warning comes on often
  Cause: Compressor can’t keep up with demand

4. Excessive oil in air lines or air dryer

• Oily residue in tanks or dryer

• Oil blowing out of air dryer purge
  Cause: Worn compressor rings or seals (very common)

5. Unusual noises

• Knocking, rattling, grinding

• Loud ticking that wasn’t there before
  Cause: Mechanical wear or internal damage

6. Overheating

• Compressor runs extremely hot

• Burnt smell near compressor
  Cause: Restricted air flow, lubrication issues, overworking unit

7. Air dryer purging too often

• Dryer purges constantly or irregularly
  Cause: Compressor struggling to maintain pressure

8. Engine performance issues

• Loss of power

• Increased engine load
  Cause: Compressor seizing or dragging

9. Coolant or oil leaks (water-cooled compressors)

• Oil in coolant or coolant in oil

• External leaks at compressor
  Cause: Failed seals or cracked head

10. Brake warning lights / alarms

• Low-air buzzer sounds

• Brake warning light stays on
  Cause: Insufficient air pressure from compressor