How to Repair Automotive A/C

Step 4 Vacuuming

It is important to change the drier each time the a/c system has been opened or loss of pressure has occurred. Since the drier obsorbs moister that may have entered the the system. When you installing a new drier make sure to drain the oil from the old one and place the same amount of new oil in the new drier. This should be done right before vacuuming, since the drier will become useless ofter two hour or so of being in the open.

Now it is time to pull a vacuum. If you are using a general purpose vacuum pump like I did and the fitting don't match the manifold gauge hoses you should go to you local a/c supply store, and the most likely will find you the right fitting for under a few dollars. Electric pumps sell for a couple of hundred dollars, so if you already own an air compressor you might what to look into an air powered vacuum pump for under fifty dollars.

Once you have to vacuum pump connected, you will need to evacuate moister and air out of the system. It is recommended that this be done when the temperature is above 80 degrees. So try not to be like me and do it in the middle of winter, if possible. Once a vacuum pump has reached nearly 30 in/Hg ( inches of mercury) let it run for a 20 min and then turn it off. If the vacuum drops a little bit that means that some water has evaporated so just turn the pump on to pull it out. Then let the vacuum sit for a minimum of 45min. If the pressure can not kept then that means that there is a leak some where in the system. Be sure to repair it before filling up the system.