After doing extensive repairs on my AC system last year, I can say that if your system is vented, even for a short period of time, it is easy to set up the gauges/valves with a vacuum pump to evacuate it properly. My local Autozone had the gauge set and the pump that I could rent for free. If your local parts stores have these for rent for free too, you might as well do it right if for no other reason than for peace of mind.

Does anyone know how much it costs for an AC shop to recover the refrigerant from a system? I'd hope that because it is so simple and because it might be able to be recycled that it might be really cheap if not free.

 

Without getting very technical I'll say this: There are a lot of variables involved with refrigeration systems when dealing with the system charge. Auto ac systems normally have very small amounts of refrigerant and when a system charge is bled off due to repairs there is no way to get the proper amount back in without evacuating all of it. What's the big deal you might ask? If the total charge is 1 lb (16 ozs) and you add 4 ozs too much you have overcharged the system by 25%. Adding more refrigerant than the system is designed for does not make discharge air colder. Bottom line is the system should be evacuated and charged to nameplate amount.

 

Do old school roll down the windows and do 70 mph air cond. I'm out ....

 

I can’t answer how successful a repair will be with no vacuum prior to charge because there are too many variables of unknown quantity. You make your bet and you take your chances. The best chance of success is to do it right but as OCD as I am about this stuff, I wing it on occasion on this and other subjects when it just has to be “good enough” for now and I don’t have what I need to go the whole 9 yards. It is absolutely true that these systems operate at maximum efficiency with the nameplate charge dumped in. That way you also take that variable out if the system doesn’t function perfectly after the charge. If you have experience you can sneak up on the right charge and get pretty close, I do it on occasion but a weekend mechanic is not likely to get that right. Something like 60% of all refrigeration and air conditioning is overcharged if the system was opened and serviced, including all professional work. More is definitely not better and can even kill the compressor from slugging in some intolerant systems. Most vehicles have some headroom for error because of the accumulator.

in the future, there is a tool to do a schrader valve change and not perturb the refrigerant charge:




George

 

Sounds like that would be a "no."

 

Thanks for giving me some confidence to keep the new charge in. The new valve was put in fairly quickly. AC blows cold