Thanks Joe..... I do have a vacuum pump, but I did not evacuate do to the fact that I still had positive pressure remaining in the system. I filled using my manifold gauge set and nothing indicated I had too much pressure (i.e. air) in the system that would inhibit all R134a to escape from the can. It is much easier to fill with the larger cylinders that you used....I may think about that the next time..... Thanks, Anthony
Suck it down. It makes a huge difference. When done close off the line on your manifold guage set and see if it will hold the vacum overnite. If it does you should have a very well sealed system. The Vacum also helps get the freon into the system. When you first open the can or cylinder it will pull it in fast because of the vacum. Glad I could help.
Don't 'evacuate the system' because 'it's a good idea because it might have air in it'. With gauges, a thermometer, & a pressure-temp chart for your refrigerant you can easily do 'static pressure test' to tell if your system has any air in it, and even how much air. Just let the car sit over night, then measure the temperature & system pressure. High & low pressures will have equalized to the same value. The pressure should be extremely close to the chart's pressure for that temperature. If the static pressure is higher than the chart's pressure for that temperature, the difference between the two pressures is the pressure of the air in the system(a simple application of Dalton's Law of partial pressures). A psi or 2 of air has negligable effect, 5psi of air is marginal, & 10 or more psi is enough to significantly reduce cooling capacity & evacuation is strongly indicated. If the static pressure is significantly below the chart pressure, your system is undercharged to the point that there is no liquid refrigerant in the system. Add refrigerant & repeat the static test after the high & low side pressures have equalized. At that point, there's so little refrigerant in the system you could also just go ahead & evacuate it, then do a full recharge. BTW, The york type compressors use a liquid film seal which will leak air under vacuum, so long vacuum leak test can falsely indicate a problem that isn't there. My car's system will hold a vacuum for 15-20 minuites, then suddenly the pressure starts rising. However, it will hold a refrigerant carge w/o detectable loss. Oh, yes, the York seals will leak about 2 oz/year of refrigerant. Modern leak detectors can detect leaks of less than 0.1 oz/year, so will squeal their heads off if you put them up next to the seal. An well known service station scam "your compressor is shot, just listen to the leak detecter'...
Don't evacuate the system? Well that goes against everything I have ever heard about charging ac systems. Down in "South Georgia" we know what 100% humidity and hot weather feels like. It has always worked for me. Putting freon cans in "hot water" to get all the freon out and preasure charts ect. You guys are making this complicated.
Verell, thanks for the tip concerning the compressor seal - I did not know that! Now, when I first measured the static pressure of the system it was approx. 25 psi (as indicated in my initial post) - which is well below what should have been indicated on a 75dF day! It was well undercharged, but we said since it still had positive pressure, moisture/air should not have been a problem, therefore no evacuation was done. I have added to the system as I described, but it is still not completely charged - have not gotten to it again just yet. Thinking out loud here.... Suppose let's say the static pressure is correct, but one knows the system is undercharged, then as stated by Dalton's Law, air must be contributing to the pressure to bring the readings up to a "normal" level. So, the static pressure measurements being equal to figures given in the tables are for a fully charged system. Static pressure alone can not indicate the health of a system as far as charge is concerned..... Anthony
Dry nitrogen is also good for verifying leaks in system. It is inert and will not be subject to rise and fall in ambient temps. Leaving a gauge overnight will tell you appx what kind of leak you may have. Pressurizing to 150 lbs or so then use soap bubbles to check connections and seals. Of course you may not be able to check the whole system without a leak detector. But most major components will be visible. Several nitrogen sweeps (3) with a vacumn pump ensure a complete and dry system. Adding a little R-22 to system makes it easier to check leaks w/ electronic detector. R134-a molecules are like comparing marbles to basketballs (r-12). Old seals and hoses can actually leak where r-12 would even be more difficult to detect. New oil chg in system can affect old seals etc. Bubbles in sight glass do not mean air in system. There are several reasons for this but I won't bore you with the details. A properly weighed in charge can still result in bubbles. I had a completely flat system after having some work done (30K). I found the discharge roto-lock on comp. completely loose. Upon further inspection I found the neopreme seal was squeezed out of its seat, and a small amount of flashing kept the nut from tightening properly. The surface was slick and vibration would eventually loosen. A utility knife took care of the problem. BTW my system had been previously converted but old fittings left in. Notes were made on comp. 87 328. Also charge the refrigerant using liquid not vapor. If you hold the can one direction you pull vapor off the top (can gets cold, pres reduces and you can't get the whole can in). By inverting the can you can chg liq. directly into system. Hope this helps.
The accuracy of a static test only requires that there is enough refrigerant in the system so that some of it remains in the liquid state. That's roughly a half charge or more. The primary purpose of a static test is to determine if the system has a significant amount of air in it. Didn't say it was a complete health check... Charging with liquid is NOT something I'll recommend to someone who's just starting A/C work. It's strongly discouraged by A/C manuals for good reason. If the liquid is introduced to fast, it can hydraulic lock the compressor & cause real damage. Heating the can with water gets the refrigerant out safely & thoroughly.
Thanks Verell, ....I did not mean to imply that you meant it was a complete health check.....I was just thinking out loud so to speak....sorry about that....your help is always welcomed and appreciated! Thank You, Anthony
Verell. Yes, you are correct. I didn't qualify the charging by liquid method. Just forgot, I take this for granted. This takes experience above what most of us have. Metering in liq. by using hand valve on gauge and watching pres. should have been added. Sorry, I've done this every day for 20 yrs. I got lazy. Just shoot me!
