Automotive Air Conditioning Information Forum (Archives)

Provided by

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

Auto A/C Flushing Procedure

TRB on Mon February 23, 2004 4:53 PM User is offlineView users profile

Procedure Arizona Mobile Air Inc. follows when flushing a system to remove debris and oil from an automotive air-conditioning system.

1. Each individual component needs to be flushed separately. Removal of hoses or any other devices may be needed for proper flushing.

2. Flush system with either an A/C flushing agent or products such as Mineral Sprits, Hecat Safe Flush and Paint Thinner. Careful with Paint Thinner for obvious reasons. Helping to get the flushing agaents through the system componets are the Santech Flush Gun Kit or for the professional the Hecat Professional Flush Equipment. We do not recommend aerosol flushes as they are not cost effective in our opinion. After using flushing agent use compressed air to blow any residue left behind from the flushing process. It also helps to place you finger or a shop rag on the opposite end to create some back pressure to dislodge any debris. It's best to perform this procedure many times in both directions to achieve the cleanest system possible. After you think its clean do it again you can never have a clean enough system. Some condensers are very difficult to flush and may need to be replaced. Cheaper replacing them then to have debris and burnt oil left in the system and damage new components.

3. Do not flush any of these components accumulator/drier, compressors, expansion valves/orifice tubes and any hose assembles the have either a muffler or filter attached to them. These items need to be replaced.

4. Our company will use Nitrogen after the flushing stage as a finial flush to remove any moisture that maybe left behind by the shop air.

5. At this point you are ready to replace the damage components along with correct oil type and amount. System should be evacuated and recharged per OEM guidelines. Evacuation should be done for a minimum of one hour. Charging capacities very from vehicle to vehicle. So it is best charge to OEM listed capacity when available! Conversions can be changed by pressures trying to achieve as close to the OEM R12 capacity without creating a high pressure issue. Complete set of refrigerant gauges are needed for this as you will need both low and high side pressures to perform these tasks.


When considering your next auto A/C purchase, please consider the site that supports you:

Edited: Wed April 13, 2016 at 5:22 PM by TRB

HECAT on Tue May 16, 2006 5:23 PM User is offline


Benefits, Problems, Procedures, Chemicals, Purging & Additional Info

The Benefit for both you and your customer is to be sure the job is done right the first time and that the repaired A/C system will operate properly for many seasons.

It is recommended to always flush the heat exchangers whenever you open a system for repairs and/or to replace components. The only way to know for sure what contamination lies inside the component is to flush it out. Was the system previously over charged or undercharged with oil? The only way to know how much oil to put back in a system is by first removing all the old oils. To prevent costly premature failures and comebacks you should flush the evaporator, condenser, and associated hoses. Replace or “oil flush” the compressor, never flush a compressor with a chemical. Replace the filter/dryer, expansion/orifice device, and put back into the system the exact amount of oil per the manufacturers specifications.

The Problems are primarily with the effectiveness of the cleaning process chosen and the recovery and removal of the flushing chemical chosen.

Some cleaning processes have shown that the waste oils were being removed but there was still evidence of metal particles being blown out during the purge process. This shows the ability of the flushing chemical chosen to wash out the oils but the process used to run this chemical through is lacking in the velocity required to remove the metal particles and they were washed over. Be aware that most traditional flush guns, aerosol flushes, and “pour in” methods alone do not produce the velocity required to blast all the contaminants out of the component.

Removal of the flushing chemical is not a prevalent problem with “tube & fin” components but rather with the “parallel flow” or “open chamber” components that are most common today. The "well" found in the bottom of many evaporators where the flush can pool, is the area of most concern when it comes to leaving any flushing chemical in the system. This is also an issue of concern with mufflers and it is recommended not to attempt to flush hoses with mufflers. The goal is a clean and dry components, leaving residual flush in the system will dilute the oils and possibly cause a future compressor failure and many other theoretical problems.

The Procedure is to chemically flush the heat exchangers (Evap. & Cond.) only, possibly with hoses attached. The other components must be cleaned by other methods or replaced and the system cannot be flushed assembled.

The condensers inlet is at the top and as with all heat exchanger flushing, this must be back flushed first (bottom to top) to back out possible large debris (compressor failure) that cannot be driven through the small passageways. This is followed by a flush in normal flow direction (top to bottom) to allow for gravity to assist in the complete removal of the flushing chemical during the purge process (see below). Some condensers pose unique problems as outlined in the “additional info” found later in this document

The Evaporators inlet is at the bottom and therefore only one flush in the back flush direction (top to bottom) is required. By isolating the rear Evap. and bypassing the expansion device you can and should flush rear Evap. units. While disconnected from the rear Evap., the long hoses can be connected together at one end and flushed like another component.

Repeating these steps back and forth can be done as many times as the technician feels necessary to achieve his or her personal satisfaction. You can never flush too much!

In addition to commercial A/C flushing Chemicals, paint thinner, mineral spirits, lacquer thinner, carburetor cleaner, brake cleaner, and other aggressive and even potentially regulated products are being used and recommended. It is the technicians desire to clean the system and it is his or her responsibility to do no harm; therefore it is the technician’s responsibility to research and use the chemical he/she is most comfortable with and is acceptable for use in the equipment chosen for the process. When isolating a heat exchanger there may be no seals involved but it is still highly recommended that the flush chosen be compatible with all system materials. The best recovery and removal of residual flushing chemical will come with the use of the more evaporative solvent-based products. The lower flash point and boiling point the better and always be aware of flammability. Also be aware of what the misting product will do to your health and the vehicles paint.

You should always Purge the remaining chemical from the component with dry nitrogen or very dry shop air. A dedicated and large inline filter should be used to insure that you are not contaminating the component with moisture if using shop air. Purge from the highest point (top down) to allow gravity to assist with chemical removal. This is why a highly evaporative chemical should be chosen. Remember just like with the flushing process, you cannot purge too much!

Some “additional info”:

“Black Death” is phenomenon that seems to have been addressed by the Blue Oval manufacturer and may not be such a prevalent problem for the future as it has been in the past. Many theories surround the root cause of this problem. The overheating and “death” of a compressor, burning the oils in the system, combined with “plastic” or “Teflon” materials will form a hard, carbonized, and sometimes impossible to remove buildup primarily in the condenser. Warning: This “death” does occur in other makes and models apparently not as frequently as to be named. Most flushes available will not breakdown this carbonized buildup and overall flushing has had very limited success in resolving this problem. A quick shot of air can be used to see if the condenser is solidly blocked. If it is, you should replace the condenser. If it is not hard clogged, at the discretion of the technician, you may be able to successfully flush.

Preventive Maintenance: As an A/C system ages on a high mileage vehicle without a compressor failure or any other apparent problems, the oils breakdown and begin to loose some of their lubricity. As this occurs these deteriorating oils begin to form a contaminant holding sludge. As the compressor wears it puts fine wear particles into the system that on their own are small enough to pass through most screens, orifices, and expansion valves. When these fine wear particles combine with the oil sludge the problems begin. The orifices and screens will begin to clog. The efficiency of the evaporator and condenser are compromised. The lack of clean oil, and the effects the contaminated sludge will have on the compressor begins the “Domino” effect towards system and or compressor failure. Periodically you should flush the system to remove these contaminants and replace the refrigerant oils to protect the system and keep it operating efficiently. Proton, a Malaysian automaker, is the first OEM to identify and implement a 60,000-mile service interval for an A/C system flush and refrigerant oil change.

Conversions: Although the majority of older R12 cars have already been converted, there are still some out there to be done. Because the mineral oil used with R12 systems must be removed and replaced with PAG for use with R134a, flushing is the only way this can be done effectively.

Sealants: These products are supposed to be harmless to the system. But an accumulation of anything other than refrigerant and refrigerant oil will have a negative effect on the performance of the system. It seems that sealants do not have the same negative effect on flushing equipment as they have had on recovery and recycle equipment. Use only flush and equipment that is approved for the removal of sealants. Warning: If you suspect sealants were in the system you just opened, it is critical to flush immediately before any remaining sealant tries to harden in the heat exchanger components.

Your Warranty & Reputation: Flushing is a proven way to reduce the expense of comebacks and warranty repairs. Keeping your customers repair costs to a minimum and providing repairs that give long trouble free service will only strengthen your reputation, profitability, and gain you more referrals.

Compressor warranty: Evidence of not flushing the system (contamination found in the unit) is a sure way for compressor manufacturers to deny a warranty claim. Most compressor manufacturers state the system must be flushed in order not to void their warranty, but few if any of them offer up an approved or recommended method.

Screens are great for providing compressor protection but they should be installed after flushing and not as an alternative to flushing. If you do not first flush then the screen will rapidly clog with contamination and starve the compressor of oil. Larger mesh screens that can catch large debris and will not so easily clog are recommended.

Disclaimer Note: Regardless of what equipment, method, and chemical you choose to use, it is ultimately the technician’s responsibility that the flush chosen is all removed to be sure this process has a positive, rather than a negative effect on the system. You must choose a product that will readily evaporate and leave no residue. It is recommended you use only flush products and processes specifically designed for flushing A/C systems. Always follow or exceed the chemical manufacturer’s recommendation on how to purge or recover the remaining flush.


HECAT: You support the Forum when you consider for your a/c parts.


HECAT on Tue June 03, 2008 11:10 AM User is offline

HECAT has published a 20 page tech article covering the basics of Heat Exchanger flushing.

This article provides insight and understanding that is crucial to heat exchanger flushing success. It covers the chemical and physical requirements, what works, what does not, and why; as well as specific sections regarding A/C component flushing, transmission oil cooler flushing, and engine cooling system flushing.



HECAT: You support the Forum when you consider for your a/c parts.


Back to Automotive Air Conditioning Procedures, Tips and FAQ.

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.