Originally Posted By: Gokhan
You might want to take it to an A/C shop. A/C jobs aren't meant for DIYers.
Don't let people like this discourage you. He is probably in the AC industry, which is notorious for spreading fear, doubt, and even misinformation in order to prevent people from fixing their own a/c and to try and get them to pay someone to do it instead. I had people try to tell me the same thing, but recently finished replacing my wife's compressor, at a cost savings of about $400, even including the price of the tools I had to buy, over what a shop was going to charge me.
Doing a/c work can be a lengthy process, as there are some steps that should be taken every time the system is opened, regardless of the repair performed. First you will need to locate the leak. The easiest way is to add some refrigerant and UV dye and then drive until the a/c blows warm again. This will mean it has leaked out, and you can use a UV light to locate the dye at the source of the leak. Then replace the part that is leaking.
Even if it is not the source of the leak, you will need to replace the receiver/drier because it has been exposed to air. Install the new one as the
last step prior to vacuum pumping the system, and do not remove the caps from the ports before this. You want as little air (and thus moisture) getting in it as possible.
While you are in there, I would check the orifice tube as well. It has a fine mesh screen that acts as a filter for the a/c system; replace it if it is dirty. If you want to be really thorough, go ahead and do a full flush on all the hoses, the evaporator, and condenser (I would recommend it if the orifice tube is dirty, otherwise you can probably get by without it). If you do this, though, you will need to add the proper amount of oil back into the system as you will have removed it all except what was in the compressor. Since you're replacing the receiver/drier anyways, you may need to add oil to the new one anyways (I did on the wife's car). Replace the o-rings on any connections you have opened for good measure (AutoZone sells a kit for about $4), put everything back together, and apply vacuum. Close off the system and make sure the vacuum holds to ensure there are no leaks. Fill with the proper amount of 134a which should be listed on a sticker somewhere in the engine bay, if not in your service manual.
Most of this should be covered in the service manual, and there are plenty of YouTube videos on vacuuming and flushing the system. In addition to your manifold gauges, you will need a vacuum pump and flush gun, both of which can be loaned from AutoZone.
Vacuum pumping:
https://www.youtube.com/watch?v=F5w3lR88fqQ
Flushing:
https://www.youtube.com/watch?v=Lnu8hA9F9S4
The evaporator and condenser will need to be flushed while they're still in the car unless you want to do a lot of extra work removing them. It will be messy, but use a rag to catch (most) of the solvent and oil that sprays out the other end. I still made a mess in the engine bay, but nothing a carwash and engine degreaser couldn't fix.