3955096 | Genuine Cummins® 1 Cyl Air Compressor For Cummins Engines

• Ram 4500/5500 chassis cab (Cummins ISB 6.7)
• Freightliner medium-duty trucks
• International medium-duty trucks
• Peterbilt medium-duty trucks
• Kenworth medium-duty trucks
• Blue Bird and IC school buses
• Various municipal, construction, and vocational trucks with Cummins ISB/QSB engines

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