Repairing Car Air-Conditioning system (Part 3)

One has located the leak. This article will describe how to replace the component and charging the system with Freon gas

What do I need?
Besides having to buy the replacement spares, one would need:
a) a set of new O-rings for the joints. Ask the shop owner for them to be supplied correctly if the spares do not come in a complete set. There are different sizes of O-ring for different parts;.
b) A new filter/dryer. Take the opportunity to replace the filter/dryer if it has not been replaced after some operation;

Make sure one would have the following things ready as they would be needed after the repair unless one is to send the car to a workshop for charging up the Freon:-

a) The high/low pressure gauge (or manifold gauge);
b) The vacuum pump;
c) The compressor oil ;
d) A tank of correct type of Freon.

Next Step
1) Replace the faulty component as required. Replace also the O-rings;
2) Replace the filter/dryer after removing the existing pressure switches and/or pressure relief valve if any and reinstall them in the new filter/dryer. Replace the O-rings as necessary;
3) Make sure the components are all in place and one is now ready to charge the system with Freon.

Since the Freon has been discharged, one would expect air trapped inside the system to be removed by vacuuming;.
1) Hook one end of the low pressure hose (blue) to the nipple valve that is attached to the suction pipe of the compressor. Hook the other end of the yellow hose(yellow) to the vacuum pump’s nipple valve. Before starting the vacuum pump, ensure that the operation valve of the suction pressure is left fully open (valve underneath the blue gauge);

2) Allow vacuum pressure to go up as high as possible. Normally, it should be more than the water boiling point pressure; for example,
water will boils @ 80 degreeF @ vacuum pressure of -29 inHg

3) Shut off the vacuum pump and allow the pressure to stand for about 30 minutes and observe the pressure. If the repair is effective, the pressure should stay at the same pressure without any loss in pressure; otherwise, suspect a leak in the repairs. Use soap detection method to detect any leak if necessary.

Charging up
If the repair is effective, the system will be ready to be charged up the Freon.
1) Close all valves on the pressure gauges. Remove the yellow hose from the vacuum pump but do not remove the blue hose that is already connected to the suction end of the compressor;
2) Charge compressor oil into the yellow hoses or use proper oil injector to charge. The amount of oil to be charged will depend on the type of repair or oil leakage. Normally, assume 80% will be lost if one drained the compressor empty; otherwise, assume about 15-20% loss in oil. For information, car air-conditioning system would normally has 300-350 cc of oil;
3) Remove all other attachment and tools from the engine compartment;
4) Startup the engine and run it at idling speed; ensure that there is no unusual noises; otherwise, stop the engine and investigate;
5) If all is well, open the valve at the Freon Tank first. The blue pressure gauge should hit around 70 psi. Now turn on the valve at the suction end of the pressure gauge (blue). The pressure should drop quickly as the valve is being opened;
6) Control the valve such that the suction pressure would stay in the range of about 30 psi to 35 psi; do not let the pressure goes above 45 psi;
7) Observe the sight glass on the filter/dryer. If the Freon is not adequate, the sight glass window will be whitish in color, caused by bubbling of Freon. Further addition of Freon should clear the bubbles especially when one rev up the engine a little.


On occasion that the sight glass window is still whitish or the Freon bubbles are still visible after some time of charging, suspect some trouble with the system or the compressor.

Testing and Commissioning
Do a test on the air conditioning system, the air vent should now blow cooler air if the repair is effective and system fully charged up with Freon. To ensure proper work is done;
a) make sure the engine and air-conditioning are running smoothly;
b) Check the area of repair for possible leak using gas detector or just plainly, performing a soap bubble test;
c) Check that the pressure gauges stay within range, with suction or low pressure around 30 -35 psi; if needed be, hook up the red hose to the discharge nipple of the compressor, one would expect a reading of around 200 psi depending on the type of Freon and the ambient temperature.

Other Related Sites

1. Car Aircon Compressor Repairs
2. Car Air-conditioning Part 1
3. Car Air-conditioning Part 2

4. Car Freon Charging for Novice
5. Car Safety Inspection and Check at Home
6. Replace Engine Oil by Vacuum
7. Wheel Alignment Using Sideslip meter

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