How to Flush an Auto AC System

by Don Bowman

Lack of cooling or intermittent operation is the deciding factor in whether or not to flush an air conditioning system. The cause is either too much oil or moisture contamination of the oil, causing it to gel or clog up one of the components. If the condenser, evaporator, dryer/accumulator or orifice device becomes clogged, the air conditioning system will be less than proficient. It is illegal to release the Freon into the atmosphere so the necessary reclaimer must be used to accomplish this procedure.

Raise the hood of the vehicle. Check the reclaimer and make sure that the high side and the low side have the knobs in the off position. Turn the valve on the recovery tank in the rear of the machine to the "on" position. Attach the blue line on the reclaimer to the low side of the A/C system. The low side, or suction side, is the largest of the A/C lines. Unscrew the blue cap from the Schraeder valve and install the reclaimer line. Turn the valve of the head of the line clockwise to the "on" position. Hook the red, high side hose to the smallest of the A/C lines. Turn this valve to the "on" position.

Plug the reclaimer into an electrical outlet and turn the machine on. Open both valves under the red and blue gauges. Press the button (on the machine) to evacuate the system. Allow the machine to remove the Freon and store it in the storage tank. When the red and blue gauges show zero pounds of pressure, the machine will say "Complete." Once this is displayed, press the "Vacuum" button. The reclaimer will display a time of 15 minutes. Press "Enter" and then press "Vacuum" again. The machine will vacuum the system for the 15 minutes, putting the system in a 30 inches of mercury vacuum conducive to evaporating any moisture and removing the last of the refrigerant oil.

Close the valves on the reclaimer under the gauges when the machine displays "Complete." Turn the machine off and remove the red and blue lines from the A/C system. Turn the valves on the lines counterclockwise to close the valves before removing.

Remove the high side lines at the condenser using the A/C wrenches--these are the small, short lines close to the condenser. Remove the low side line at the evaporator by the firewall using the same wrenches.

Remove the low-side line at the accumulator using the same wrenches. Disconnect the low-side electrical switch on the accumulator by squeezing the connector and pulling it out. Loosen the bracket holding the accumulator to the firewall or fender well using a small wrench. Discard the accumulator. Remove the orifice tube located inside the high-side line that comes from the condenser and leads to the evaporator. It will be inside the line closest to the condenser. Remove it with the needle nose pliers, paying attention to its orientation when removing. Discard the orifice valve.

Pour the A/C flush into the flush bottle on the reclaimer and close the cap. Pressurize the reclaimer to 80 pounds. Insert the hose into the evaporator inlet for the high-side line and allow the fluid to be pushed through the evaporator until the bottle is empty. Repeat from the beginning of Step 6, only this time, insert the hose in the condenser (use the inlet side from the compressor to the condenser line).

Blow the evaporator and condenser out for three minutes each with the air blowgun. Reconnect the high-side line to the evaporator. Slide a new orifice tube into the opposite end at the condenser. Screw this line onto the condenser and the line from the compressor to the condenser. With each line end, make sure that the o-ring is in place and undamaged. Replace the o-ring if it is torn or damaged. Using the A/C wrenches, tighten all lines. Pour 6 ounces of 134 refrigerant oil into the new accumulator. Place the accumulator into the bracket. Screw in the line at the evaporator and then the line to the compressor using the A/C wrenches.

Reconnect the high- and low-side lines from the reclaimer to their respective Schraeder valves and open the valves of the end of the lines by turning clockwise. Turn the reclaimer on and open the valves under the gauges. Push the button for "Vacuum" followed by "Enter" and once again "Vacuum." The machine will vacuum for 15 minutes to remove all the air and prepare the system for a charge.

Charge the system when the machine displays that it is finished vacuuming. Look at the placard under the hood (on the left side) for the amount of charge for the A/C system. Press the button for "Charge" and the machine will ask you for the amount of charge. Press the numerical buttons for the proper charge (as read on the placard) and then hit "Enter." The machine will display oil charge--at this time press the top button on the machine above the obvious oil container bottle. Hold the button down until the oil bottle drops by 4 ounces. Release the valve. Press the charge button and the machine will automatically charge the system with the proper charge.

Close the valves on the reclaimer under the gauges and the valve on the storage tank on the back. Remove the high and low side lines when the charge is complete. Turn the valves on the lines counterclockwise and remove them from the vehicle and screw the red and blue caps on to the high- and low-side Schraeder valves respectively.

Warning

  • close The air conditioning system is pressurized. Take care when attaching the reclaimer hoses to the system Schrader valves.

Items you will need

About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).