How Do You Flush Out an Auto AC System?

Lead Image
  • 4-8 hours
  • Advanced
  • 1,500-3,500
What You'll Need
Hand tool kit
Larger than 1" open end wrenches
Manifold gauge set
Vacuum pump
Refrigerant recycler
Solvent or flush liquid
Shop air
Refrigerant recharger

Auto air conditioning systems may require flushing after a catastrophic failure of the compressor, since debris from the failed unit can scatter throughout the closed system.

This debris will be the broken parts of compressor—reed valves, piston rings, maybe even parts of a disintegrated piston and metallic scrapings from internal cylinders of compressor. If this detritus isn't cleaned out, it will eventually cause another failure.

Vehicle AC Flushing Equipment

A good selection of hand tools, including end wrenches larger than 1” to disconnect hoses and component fittings, will be necessary.

A refrigeration manifold gauge set will be invaluable, along with a vacuum pump, refrigerant recycler, and recharging kit.

The task is done in a series of steps in sequence. If you don't have the required tools and/or expertise, ask your friends if anyone has the expertise and can assist you. Some steps may need to be ‘hired out’ to a shop with tools and expertise. The tasks you can accomplish yourself will save you some expense.

If you're uncomfortable attempting the job, by all means hire it out to a professional. The information provided here will help you make that decision.

machine connected to car engine for AC flushing

Evacuate Remaining Refrigerant

Safety Note: Refrigerant can be dangerous. It's pressurized, and will get extremely cold when depressurized. Safety goggles are strongly recommended while handling refrigerant. If it splashes on your face, refrigerant can freeze your eyeballs, causing blindness.

Depressurize the system by evacuating any refrigerant that remains. A refrigerant recovery system should be used to accomplish this task. If you don't have a recovery system, don't try to get the fluid out another way—take the vehicle to your local repair shop and pay them to remove the refrigerant.

Disassemble Components

To assist in reassembly, take a picture of the engine area before disassembly to have a reference for reassembly.

hands taking a picture of the contents of a car engine

Remove hoses and hang them vertically over a container to let them drain out refrigerant oil as well as possible. Remove the accumulator/receiver-dryer. Remove orifice tube or expansion valve (whichever your vehicle uses).

Flush Each Component

Use flush liquid or solvent and shop air to clean out the hoses, evaporator core, and condenser. The market supports several brands and types of solvent and/or flushing liquids.

The condenser will have the most debris of any component and may not be flushable. If this is the case, you'll probably need to replace it.

Pour the chosen solvent or flushing liquid into each component and then blow in each direction with shop air. The cleaning is finished when no more debris is blown out, the solvent or flushing liquid is clear, and air blows through the component easily.

air gun for cleaning engine parts

Exceptions Not to Flush

Don't flush accumulator/receiver-dryer, it will be replaced as required to maintain warranty of the new compressor.

The high pressure hose that runs from compressor to condenser with built on muffler should also be replaced, since it's extremely difficult to clean the muffler portion.

There's no need to flush compressor as it will be replaced. There's no practical way to flush a compressor, due to the construction and design.

hands holding a drainage tray while flushing a car's engine

Reassemble system

Install your new compressor and new accumulator/receiver-dryer. Reassemble all components using new gaskets and O-rings. Be sure to lube the O-rings with refrigerant oil that is correct for your system. Follow instructions contained with new compressor concerning amount and type of refrigerant oil to put in system. Refrigerant oil is necessary to lubricate the internal parts of compressor.

car engine ac system getting flushed

Evacuate and Recharge

Connect the gauges to their appropriate ports and to a good vacuum pump. When vacuum requirements are met and will hold for several minutes with gauge valves closed and vacuum pump stopped, then recharge according to service manual specifications. You need to know the exact amount of refrigerant your system requires for optimum cooling performance.