Flushing Your Car's AC System

Flushing your car air conditioner system is done when repairs are needed. The failure that happened to cause it to need repairs may have deposited shrapnel and other debris in the system components and connecting hoses.

Flushing will remove the refrigerant oil necessitating a refill of the refrigerant oil. There are many types of refrigerant oil out in the market today, so consult your vehicle service manual for the correct type and amount of refrigerant oil to use.

The correct refrigerant and amount will be listed in the vehicle service manual and sometimes on a tag glued on a component of the air conditioner system. An example would be R134A refrigerant, and system fill 3.5# refrigerant.

Overview

An air conditioning system consists of a compressor (powered by the engine), hoses for refrigerant to circulate through, a condenser, an accumulator/receiver-dryer, and an evaporator.

The compressor compresses the refrigerant gas and passes it through a hose to the condenser (located in front of vehicle radiator) where the heat is removed by air flow around the condenser tubes and the cooled gas then goes to the accumulator/receiver-dryer where a desiccant captures any moisture from the refrigerant gas.

The gas then passes into the evaporator through a small passage (orifice tube) and is released into the evaporator. There are other types of expansion valve controls, but the fixed size orifice is the most commonly used system in today’s automobiles. This is known as the CCOT (cycling clutch orifice tube) system.

The sudden expansion of the refrigerant gas produces a cooling effect and the cooled evaporator has a fan forcing air around its tubing causing the auto to become cooler. This temperature change is referred to as the Joule-Thomson effect and is fully explained in Physics textbooks.

The refrigerant oil circulates through the air conditioner system with the refrigerant gas to keep all the moving parts lubricated. This oil is specific to the exact vehicle being serviced and should follow all service guidelines in the vehicle service manual.

Tools and equipment

A manifold gauge set designed for the type of refrigerant being used will be required along with all the different sizes of wrenches needed for disassembly.

A vacuum pump to remove all the air and moisture from the system is one of the required tools for air conditioner service. Any moisture left in the refrigerant gas can freeze and the resulting ice will plug the expansion tube orifice causing overpressure and system damage.

A refrigerant recycler is required for most types of refrigerant for environmental protection. Scientists and researchers have determined that most refrigerant gases are harmful to the earth’s atmosphere and should not be released in the air.

A refrigerant leak detector will be needed to check for leaks when the job is finished.

A vehicle service manual that details air conditioner service is invaluable even for a seasoned and experienced technician.

Considering the costs of all the tools required for the procedure and the highly technical nature of the job, it would be in the best interest of the vehicle owner to hire out this job to a certified and licensed professional who will have the necessary tools and knowledge to do the job correctly.

Discharge the System

Refrigerant is under high pressure and should be released into a refrigerant recycler by an experienced and certified refrigerant handler. Personal injury can occur if proper procedures for refrigerant recovery are not followed.

Connect the correct manifold gauge set to the service ports of the air conditioner system and then connect to a refrigerant recycler to capture the refrigerant and protect the environment.

Connect the blue hose to the low pressure port and the red hose to the high pressure port. The yellow hose will then connect to the refrigerant recycler and the gas flow is controlled by the valves on the manifold gauge set.

The same yellow hose connects to the vacuum pump for evacuating the air and moisture after reassembly.

A refrigerant recycler collects the refrigerant from the auto’s air conditioner system, cleanses it and can then reuse the cleansed refrigerant to recharge the system once repairs and flushing is completed. It will cost in the thousands of dollars range and is most likely beyond the financial means of the average do it yourself person.

Once the system is de-pressurized and the refrigerant recovered you may proceed with system disassembly.

Disassembly

To do a good flush, all components must be disassembled to make the flush process go smoothly and be effective. Ascertain which component or components have failed and need replaced. If the compressor has failed a flush is needed to remove the pieces (O-rings, seals, metallic parts, etc.) of the part that failed.

No need to flush a failed compressor that is being replaced. When a compressor is replaced the compressor manufacturer will require replacement of the accumulator/receiver-dryer at the same time to have a warranty for the replacement compressor. A full flush will be required also.

Maintain all your purchase receipts for proof you have followed correct procedures in case you have a warranty claim.

If the problem was a loss of refrigerant from a bad hose or leaky seal a flush may be needed to remove the refrigerant oil from the system so a proper amount can be reinstalled before recharging with refrigerant.

The amount of oil used is critical as too much will flood the system and too little will starve moving components for lubrication resulting in premature failure of the compressor.

Training and experience will be needed for air conditioner service as it is highly technical and by law requires special refrigerant recovery tools.

Flush

Eye, hand, and face protection must be used when flushing an air conditioning system as the flushing fluid is dangerous for the human body. Thoroughly flush the components of the air conditioner system to remove all debris and oil.

Flushing fluid comes in a pressurized can allowing for a good cleaning of the components, or it can be non-pressurized and be poured into the air conditioner components and then blown out with a compressed air source.

Many auto parts retailers sell a wide rubber tipped blow gun that is designed for air conditioner system flushing and blowing the flushing solvent from the components.

Be very careful where the hose ends are pointed when blowing the flush solvent from them. Your personal health is much more important than the air conditioning system.

A power flush system is available that can do a very effective flush of the system in a few minutes. The cost of the equipment is prohibitive for the average do it yourself person being in the several hundred dollar range.

Evaporators can be flushed while still installed. Remove the hoses and then flush the evaporator. This procedure will save many hours of labor and can be quite effective if care is taken to do a thorough cleaning.

Reassembly

When the flushing is complete and all components have been blown dry with a compressed air source, you can begin reassembly. If the compressor is being replaced, follow the procedure outlined in the vehicle service manual to drain the oil from compressor into a measuring to check for correct amount.

Many times the replacement compressor will be filled with too much refrigerant oil from the factory.

Mount the compressor, condenser, accumulator/receiver-dryer, evaporator (if removed) and then connect the hose assemblies in the proper places.

Use new O-rings in the hose fittings and lubricate them with the same refrigerant oil that the air conditioner system uses to help with reassembly.

Non lubricated O-rings can be damaged when reassembled causing refrigerant leaks.

Following the suggested procedure in the vehicle service manual add the necessary oil to compressor and the accumulator/receiver-dryer before connecting the hoses

Don’t forget the orifice tube that goes into the inlet tube of the evaporator. Orifice tubes are inexpensive and should be replaced any time the system is opened.

When all fittings are tight, connect your gauge set to the correct ports and then to a vacuum pump. Evacuate the system for several minutes until gauge reads a negative reading of near -26” on the dial.

Vacuum is measured in inches of mercury. A near perfect vacuum will be reached at -32”. Very few vacuum pumps will manage this measurement. Any reading of -26” or more will evacuate the air and moisture from the system and give good cooling results.

Shut off vacuum pump and gauge valves and wait several minutes.

Make note of gauge reading at shutdown and check if any vacuum has been lost during the wait time. If vacuum is lost during this time, find the leak and repair it. If no vacuum is lost proceed with the final vacuuming procedure for about an hour to remove all the moisture possible from the sealed air conditioner system.

Refill With Refrigerant

If the system will hold the measured vacuum for 5 minutes with the charging manifold valves closed you may then recharge it with refrigerant. Be sure to use the correct refrigerant for the vehicle as it was designed to use.

The proper procedure for refilling the air conditioner system is to use gaseous refrigerant, not the liquid form. Either use the proper number of small cans of refrigerant or use a large cylinder of refrigerant placed on an accurate scale to calculate the correct amount of refrigerant to recharge with.

Consult your vehicle service manual for the correct amount of refrigerant to fill the system with. Most systems are very critical for the amount of refrigerant. Too much refrigerant will not cool properly and too little refrigerant can cause “freeze-ups” and the system not cool properly.

The refill can be checked for correctness by comparing operating pressures to an established temperature pressure chart for optimum cooling.

When the system is refilled and has been operating for several minutes, shut off the air conditioning system and check for leaks using an electronic leak detector, especially at all fittings and connections.

Is This Procedure Within Your Skill Level?

If, after reading this description, you don’t feel comfortable tackling this procedure then by all means, hire the job out to a licensed and certified professional.

The amount of tools, and knowledge necessary to do an air conditioner flush could be beyond your skill set.

The author studied, trained, and worked at air conditioner service for several years to acquire the knowledge, tools, and skill set necessary for this kind of service.

Frequently Asked Questions

How often should I flush my auto AC system?

Your auto AC system only requires a flush when it is being serviced for some problem such as compressor failure.

How much does an auto AC system flush cost?

A flush can cost from a couple hundred dollars to several hundred dollars (2023) depending on your locale and the competition between shops for the service contracts. Also depends on the individual brand of the vehicle being serviced and how complicated the service will be.

Can You Flush a Condenser?

Yes! Flushing a condenser is a part of the flushing process and can be accomplished without removing it from the vehicle. Use a pressurized system and flush it from both directions. Flush through the inlet (compressor side) and then through the outlet (accumulator/receiver-dryer side).

The condenser may need replaced if your air conditioner system had a compressor failure as the debris from that failure can lodge in the evaporator tubes blocking refrigerant flow.

Should the hoses be replaced during a flush procedure?

If the vehicle being serviced is more than 5 years old, it would be good preventive maintenance to replace them because they harden with age and the under-hood environment. Usually hoses cost less than a system refrigerant refill made necessary from leaky hoses.

What kind of refrigerant oil to use?

Use the type of oil recommended in the vehicle service manual for the air conditioner system. Mixing of different types of refrigerant oil can result in bubble gum like sticky mess with no ability to lubricate. Use the suggested amount of oil. Under fill and over fill are both harmful to the system components.