I know this is something usually left to pros, but I’m talking about a 25 year old Peugeot here, worth maybe a few hundred bucks, so I can’t pay a lot to revive the a/c. I have a vacuum pump and the recharge hoses, a replacement receiver/dryer, and the right refrigerant and oil. The question is, how do I get out all of the old refrigerant? Put a vacuum on the low side? Will putting a vacuum on it be enough? Do I apply pressure and blow it out? They also say to flush the system. With what?
If your system has R12, you absolutely cannot just evacuate it. Even if you use a vacuum pump the VP exhaust is going to the atmostphere. Check with a qualified HVAC shop, they might evacuate the system for free or maybe even give you money for letting them recover the R12 and sell it to a customer who needs it.
In days of old, the R12 would be exhausted through the gauge set with the charge line to a spare oil containter to collect any oil that was carried with the discharge. When the system was down to atmosphere, parts were replaced as needed; a new receiver dryer installed if the system had leaked down to atmosphere; a vacuum drawn till steady plus 30 minutes to an hour; the system brought up to can pressure; leak checked with an electronic sniffer; oil was added to the compressor; and then the correct weight of R12 was added to the low pressure side.
If you are going to flush the system, you will probably have to blow it out with dry nitrogen after disconnecting the hoses at the compressor or using the isolation valves and taking out the expansion valve and disconnecting its hose(s). You will have to measure and fill the oil level in the compressor to spec once all the oil and debris is out of the external components.
Working on AC systems used to require a lot a tools, knowledge, and experience. Now that same applies with the added requirement that enviornmental laws be adhered to. Don’t do this unless you invest in the tools and education and are willing to do it right.
I do not believe in R-12 harming the ozone layer, and I don’t believe in Global Warming. I do, however, believe in attempting to comply with all laws to the best of my ability, even when I think they are stupid. The day they tell me it is illegal to use my fireplace here in rural mountain Mexico will be the last day I use that fireplace. At that time, I will probably spend a fortune installing a solar heating system. So, I agree with Researcher on this one.
This must be an R-12 system, right? If there is any pressure at all in the system, it can’t be leaking THAT bad…Why not first try adding a can or two of an R-12 replacement like “Freeze-12” and see what happens before you invest a lot of money “restoring” the system?? As you said, this is a $300 car…This procedure has worked for me on 3 or 4 older cars, the desired results were obtained.
Another down and dirty trick. With the engine off, remove both high and low side schader valves with a tire stem tool. Let all the freon, if any, escape. Then, on the low side, blow in a can of 134a and let it blow out the open high-side port. Close up the system and recharge. I know there will be howls of rage over this, but it’s your car and you can do what you want with it. When you buy freon legally, you can do what you want with that too. Sooner or later, it ALL leaks into the atmosphere anyway. Please, please, at LEAST wear eye protection when working with refrigerants.
Exactly why are you wanting to empty the system in the first place? Most older systems wind up emptying themselves due to leaks.