Tool Briefing: A/C System Flushing

When an A/C system has suffered damage or been serviced improperly, it can cause confusing symptoms. Often the best way to diagnose a system is to return it to a known state of charge. Simply recovering the refrigerant and evacuating the system isn’t always enough to remove all the oil and possible contaminants, and many techs decide to smiply flush the system.

General Motors Technical Service Bulletin (TSB) 01-01-38-006C describes the GM-approved procedure for flushing the Air Conditioning (A/C) system on any GM vehicle. GM Service Operations and Delphi Thermal Systems, who supplies A/C systems to GM, worked together with dealership technicians to develop these procedures. The Bulletin provides guidance to help a tech decide whether a system should be flushed. Since the procedure takes a fair amount of time, the bulletin notes that flushing is needed only in the event of desiccant bag failure, gross overcharging of PAG oil and/or when any kind of contamination is found in the refrigerant system.

Flushing will reliably remove excess oil or dye, sealers, loose desiccant and other contaminants that are introduced (accidentally or intentionally) while servicing the system. Often a technician will flush a system in an effort to remove debris left behind after a catastrophic compressor failure. While some manufacturers of replacement compressors require proof of flushing as a condition for honoring their warranty, the bulletin specifically states that you should not expect flushing to remove all the debris. After a catastrophic compressor failure, it is almost impossible to flush all the metal particles from flat-tube type condensers. Installation of liquid line filters or suction screens and/or condenser replacement is the only safe way to protect the new compressor from such debris. This is particularly true on systems with a muffler on the discharge line.

Tools for the job

The bulletin calls for using only liquid R-134a refrigerant as the flushing agent. It also lists all the equipment that dealerships are required to have for complete A/C service. When the bulletin was released in July 2004, every GM dealer had been issued or acquired the GM J43600 Air Conditioning Service Center, which is the ACR 2000 recovery/recycle machine built by Robinair. Although there are still many of those machines in service, the J43600 has been superseded by the GE-48800, which is the new Robinair Model 34988 recovery/recycle/recharge (RRR) machine.

The new machines were developed to meet SAE Standard J2788, which establishes performance requirements for any machine used to remove and/or install refrigerant in a mobile air conditioning system that uses R134a refrigerant. SAE J2788 sets a very high standard for accuracy to make sure that the correct amount of refrigerant is installed into the system. The best way to meet this standard is to automate many of the functions of the RRR equipment.

No shops are required to replace their existing equipment, and equipment manufacturers are allowed to sell new machines that were built to the earlier SAE Standards until existing stock runs out, but all machines built since November 1, 2008 conform to the new standard.

The GE-48800 is fully automatic and includes a cycle that will flush the whole A/C system using refrigerant as the flushing agent. This machine is the direct replacement for the ACR 2000.

Although the tools have changed and much of the job is now automated, the flushing process is basically the same. After recovering the refrigerant from the system, the procedure involves removing the orifice tube, disconnecting the refrigerant hoses from the compressor and connecting them to the RRR machine. The machine then flushes the system with clean liquid refrigerant, removing debris, oil and contaminants.

One advantage of using pure R-134a as the flushing agent is that there is no solvent to dispose of once the procedure is completed. The machine also filters that same refrigerant “to SAE purity levels” as required by the SAE Standard, so it can be used again for flushing or for recharging the system.

Hints for using the tools

When using the GE-48800 as a flush machine, first make sure that the oil separator’s drain bottle on the side of the machine is empty. This makes it possible to measure the amount of oil removed from the system during flushing. Also make sure that there is at least 10 pounds of refrigerant in the machine’s Internal Supply Vessel (ISV), often called the recovery tank. Finally, make sure the manual valve for the external refrigerant supply tank is closed. That’s because if electrical power is lost during the flush cycle, the machine’s electrically operated valves will be disabled. If the manual valve is open, refrigerant will flow from the supply tank into the recovery tank, making it impossible to recover refrigerant from the vehicle.

A separate flushing adapter is needed to connect the machine’s hoses to the vehicle’s hoses at the compressor block connection. The adapter kit is available from Robinair and other sources, and if you own the original GM J45268 Flush Adapter Kit, that will also work. The hoses can be connected so that refrigerant will flow in either direction, meaning the machine can be used to back-flush the system.

Read the User Manual

One of the machine’s automated features is a filter monitor. As spelled out in the SAE standard, the filter-drier must be replaced after 150 pounds of refrigerant has passed through it. Machines built to that Standard include software that monitors the quantity of refrigerant flowing through the filter, and once that maximum quantity has been reached, the machine will go into a forced stand-by mode. Before using the machine for anything at all, make sure there’s enough filter life to get through the job.

The user manual tells you how to find “filter capacity” data in the maintenance menu, how to change the filter and how to reset the filter monitor. The new filter has a serial number which must be entered on the keypad before the machine will reset and function normally again. While the details of filter replacement/reset procedures may differ with different manufacturers, similar filter capacity features are built into every RRR machine built to the SAE J2788 Standard.

As with any piece of shop equipment, it’s important to read the user’s manual carefully and make sure you understand how to use the machine before connecting it to the vehicle. This is even more important when complying with this particular TSB, because whether it’s the machine described here or any other new RRR machine, if it’s built to the latest SAE Standards, it will be different from any other machine you’ve ever used.