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Take it to a shop that does ac work and have them recover, evacuate and recharge the system but the question I have is why do you want to change the refrigerant?
The only legal and safe way to do it is to have a shop recover the refrigerant with an RRR (Recover, Recycle, Recharge) machine. Try your local community college if they offer a vocational program for mechanics... they might even pay you for the refrigerant they recover.
0Psia
You need to recover the refrigerant. Remove the evaporator case and disassemble it. Replace the valve and recharge the system. It is best to install a receiver drier at the same time.
How much refrigerant used to recharge the AC system in a Honda Civic depends on how much the system needs. There will be a gauge on the refill bottle which is tell the user how much is needed in that one application.
There are two ports on the air conditioner compressor on a Montana. Attach the refrigerant to the lower port and recharge the system.
There are two ports on the air conditioning compressor on the Mercury Mountaineer. The refrigerant to recharge the system is to be connected to the lower port.
Use a vacuum pump that pulls it into a tank.
That is only partially true. Legally you must repair the leak before adding refrigerant. You do not have to remove the Freon and recharge it with fresh Freon. However, this is what I would do if it were my car. I am assuming this is a 1996 or older vehicle which contains Freon (R12). I would have them remove all the R12, and give me credit for what they recover. R12 is very expensive, so don't give it away. I would then have the leak repaired and convert the vehicle to R134a. If it is newer than 1996, just repair the leak and recharge the system. You might want to go to a different repair shop, as what they are telling you is only half true. I would not trust this shop.
you will have to evacuate the refrigerant then have a vacuum pump hooked up to it and have it hold a vaccuum and then recharge the system
Short answer is that you don't. If you need to do this, then you have a certified shop recover and store it.
No, not unless you have the proper equipment to recharge the system and/or dispose of the old AC refrigerant.