A/C Oil Charge Calculator
Replacing an A/C component takes oil out of the system with it. Work out how much to add back, and convert refrigerant charge between units.
What you replaced
- Use the oil type the system specifies. PAG 46, PAG 100, PAG 150 and POE are not interchangeable, and R1234yf systems have their own requirement.
- Charge refrigerant by weight, never by pressure. Pressure gauges cannot tell you how much is in the system.
- Always replace the receiver drier or accumulator when the system has been open. It absorbs moisture and saturates quickly.
Refrigerant handling is regulated. Venting refrigerant to atmosphere is illegal in the United States. Recovery requires certified equipment and, for paid work, EPA Section 609 certification. Liquid refrigerant causes severe frostbite on contact.
Why oil leaves with the part
A/C oil circulates with the refrigerant rather than staying in a sump, so at any moment some of it is sitting in every component. Take a condenser off and roughly an ounce of oil goes in the bin with it.
Replace several components without adding oil back and the compressor ends up starved. Add too much and the oil takes up volume that should be carrying refrigerant, which costs cooling and can hydrolock the compressor. Both failure modes are common and both are avoidable by measuring.
New compressors ship full
Most replacement compressors arrive with a full system charge of oil inside, purely to keep the internals coated in storage. Fitting one straight out of the box on a system that still holds its own oil results in roughly double the correct amount.
Drain the new compressor completely, then measure in exactly what the system capacity calls for.
Charge by weight
Refrigerant charge is specified as a weight on the underhood label, and that is the only accurate way to fill a system. Gauge pressure varies with ambient temperature, humidity and airflow, so topping up until the pressure looks right is how systems end up badly overcharged.
Frequently asked questions
How much oil do I add when replacing an A/C condenser?
About 1 ounce, which is the amount that typically stays in a condenser. An evaporator holds around 1.5 ounces, a receiver drier around 0.5, and each hose about 0.5. Add the total for everything you replaced.
Do I drain a new A/C compressor?
Usually yes. Most new compressors ship with a full system charge of oil for storage protection. If you fit one without draining it, the system ends up with roughly double the oil it should have, which reduces cooling and risks hydrolock.
Can I mix PAG 46 and PAG 100?
Do not. The viscosity grade is specified for the compressor design, and the wrong one changes how the compressor is lubricated at temperature. R1234yf systems also require their own specific oil. Use exactly what the label calls for.
Why is my A/C worse after a recharge?
Overcharging is the usual reason. Excess refrigerant leaves no room for it to expand and absorb heat, so head pressure rises and cooling falls. Charging by weight into an evacuated system is the only reliable method.
Everything on this page is an estimate worked out from the numbers you entered and typical figures for the conditions you picked. Your vehicle, your parts and your conditions will differ. Check anything you intend to act on against the manufacturer's specification, the service manual, or a qualified technician. Verifying the result before relying on it is up to you.