This is a great item as long as you have reasonable expectations about what it can do. If you want a device that can pull a 29+ inches hg vacuum, then go spend a lot more money and get a real electric pump. If you want to fix an occasional A/C unit, then this is an excellent alternative to spending a lot of money on a pump you will use once or twice a year.It does use a fair amount of air to run, and I would say the 4.2 cu.ft./min spec listed is probably about right. I have a compressor that delivers 5.7 cu.ft/min @90psi, and it had no problem at all keeping up with the continuous air demand. I set my compressor for 100psi static pressure with the air line not hooked up. This gave a reading of 90psi while the unit was hooked up and running, which is what the instructions recommend. My results on a dodge grand caravan with front/rear ac (which holds 46oz Freon) were as follows:Pulled a vacuum down to -20 in about 3 minutes.Got down to -25 inches in an additional 3 minutes.Got down to -27 after another 5 minutes, and that was the max.So, it took about 10 minutes to get the vacuum down to about -27. It does not matter how much longer you run it, that is the max. However, that is more than low enough to make water boil at room temperature, so it is all you need to do A/C work. A lower vacuum may give you bragging rights, but it does not nave a lot of practical value in how well your car cools off.Final note on quality - it is your basic made in China light duty unit. I have used it twice with no issues and it does not appear to be particularly breakable. I dropped mine of the car hood onto the concrete with no ill effects. However, for the price, if I get half a dozen uses out of it I will be happy.