How to Add Refrigerant Oil

by Lee Sallings
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It is normal to lose a small amount of refrigerant oil from the air conditioning system over time. Slight leaks around seals during cold weather often cause loss of refrigerant as well as refrigerant oil. Add oil to the system when you are replacing parts like the compressor or accumulator/drier as well. Adding oil to the system is similar to adding refrigerant. However, adding too much oil to the system can cause a loss in cooling efficiency and, in extreme cases, damage to the A/C compressor. Add oil sparingly if you're just replacing oil that has been lost due to normal leakage. Refer to the manufacturer’s instructions and specifications when replacing a compressor or other component.

Step 1

Check the valves on the front of the gauge set to make sure they are closed. Attach the air-conditioning gauge set to the service ports. The blue hose goes to the low-pressure service port, and the red hose goes to the high-pressure port. Generally, the low-pressure port is on the accumulator (a round cylinder-shaped component) near the firewall, and the high-pressure port is on the A/C line connecting the condenser (the component in front of the radiator) and the evaporator (behind the firewall). The exact position of the service ports vary according to year, make and model, so consult your service manual for exact locations.

Step 2

Start the engine and set the A/C controls for max air conditioning. If there is a vent or recirculating air option, set the controls for recirculating air. Set the blower speed for medium speed. This provides the best cooling and the largest pressure differential in the system. The pressure differential is what allows the addition of oil through the low side port.

Step 3

Attach the can tap supplied with the gauge set, and attach a can of oil charge to the can tap. Turn the thumbscrew all the way in and all the way out to open the can. Open the blue valve on the gauge set to allow the pressurized oil charge into the system. In most cases, one can of oil is enough to replenish the lost oil.

Step 4

Turn off the engine, and allow the pressures in the system to stabilize before disconnecting the hoses from the service ports. This prevents damage to the service ports.

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