AC Compressor Oil Add

This procedure covers the proper method to add refrigerant oil to the AC system of a 2007 Ram 3500 with 5.9L Cummins diesel engine, typically performed during compressor replacement or after refrigerant leak repair.

Warnings

Tools required

Parts

• PAG 46 refrigerant oil × 1 — Use Mopar approved PAG 46 viscosity oil

Fluids

• PAG 46 refrigerant oil — 0.25 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely if recently operated
3. Ensure work area is well-ventilated
4. Verify you have the correct PAG 46 oil and that container is sealed and fresh
5. Connect refrigerant recovery machine to vehicle AC service ports

Procedure

1. 1

   Recover existing refrigerant
   Connect the recovery machine to both the low-side (larger fitting) and high-side (smaller fitting) AC service ports. Follow recovery machine operating instructions to completely evacuate all R-134a refrigerant from the system. Record the amount of refrigerant recovered for recharging reference. This process typically takes 15-20 minutes.
2. 2

   Determine oil quantity needed
   Calculate oil quantity based on service performed: For compressor replacement, drain and measure oil from old compressor, then add same amount to new compressor before installation. For evaporator replacement, add 3 oz. For condenser replacement, add 1 oz. For accumulator/drier replacement, add 2 oz. For minor service or leak repair where no components were replaced, add 2 oz to compensate for oil lost during recovery process.
3. 3

   Prepare refrigerant oil
   Open the PAG 46 oil container immediately before use. Measure the precise amount of oil needed using a graduated cylinder or measuring device. Keep the oil container sealed when not actively pouring to prevent moisture absorption. Use only fresh oil from a recently opened container.
4. 4

   Install oil injection tool
   Attach the PAG oil injector tool to the low-side service port (located on the larger diameter AC line on the suction side of the system). If using a charging hose with oil injection port, ensure all connections are secure and the hose is purged of air. Some technicians prefer to add oil directly through the compressor before installation if the compressor is being replaced.
5. 5

   Inject refrigerant oil into system
   Pour the measured oil into the injector tool reservoir. Slowly inject the oil into the system through the low-side port. If using a manual injector, this may require creating a slight vacuum or using system pressure. The process should take 3-5 minutes to ensure oil enters the system properly. For new compressor installation, pour measured oil directly into compressor inlet port before connecting lines.
6. 6

   Verify oil injection completion
   Ensure all measured oil has entered the system. Check that the injector tool is empty and no oil remains in hoses or measuring equipment. Remove the oil injector tool from the service port and ensure the service port cap is removed for next step.
7. 7

   Evacuate the AC system
   Connect vacuum pump to both AC service ports using manifold gauge set. Run vacuum pump for minimum 45 minutes to achieve deep vacuum of 29-30 inches Hg. This removes air and moisture from the system. Close manifold valves and shut off pump, then monitor gauge for 10 minutes - vacuum should hold steady indicating no leaks.
8. 8

   Recharge with R-134a refrigerant
   With engine off, connect refrigerant source to low-side service port. System capacity for this vehicle must be verified on the underhood AC label or in OEM service documentation before charging - do not rely on a generic figure. Charge to the exact weight specified on the label. Charge refrigerant into low-side only until system reaches approximately 80% of capacity by weight on your scale.
9. 9

   Complete charging with engine running
   Start engine and set AC controls to MAX AC, full cold, high blower speed. Continue adding refrigerant through low-side port only while monitoring manifold gauges. Add remaining refrigerant until reaching specified weight. Low-side pressure should stabilize at 25-35 PSI and high-side at 200-250 PSI at ambient temperature of 70-80°F.
10. 10

    Distribute oil through system
    Allow engine to run at 1500 RPM with AC on MAX for 10-15 minutes. This circulates the refrigerant oil throughout the system and allows compressor to distribute oil to all components. Monitor gauges to ensure pressures remain stable and compressor clutch engages properly.

Reassembly

1. Install protective caps on both high-side and low-side AC service ports
2. Secure any AC lines or harnesses that were moved during service
3. Clean any spilled refrigerant oil from engine bay surfaces

Verification

• Verify AC blows cold air from all vents with temperature approximately 40-50°F at center vents
• Check compressor operation - clutch should engage smoothly without noise or vibration
• Confirm low-side pressure reads 25-35 PSI and high-side reads 200-250 PSI at idle with AC on MAX
• Inspect all AC line connections and service ports for signs of oil leakage
• Listen for unusual compressor noises that might indicate oil starvation or overcharging
• Test AC performance during 10-minute test drive to ensure consistent cooling
• Use electronic leak detector around all service connections to verify no refrigerant leaks

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