bgambino Posted May 12, 2009 Share Posted May 12, 2009 I read here someone mentioning the need to pull a vacuum on the AC system (I am assuming this is if you disconnect a line --- like I had to do) Why pull a vacuum? I have access to vacuum pumps at work How would you connect to the fill fitting on the car? When you attach the charge hose, won't it suck the can contents (liquid) too quickly into the system?? Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted May 12, 2009 Share Posted May 12, 2009 Yes, if the system has been opened up for any reason, you need to pull a vacuum. You need to do this primarily because air contains moisture, which in an AC system can freeze and cause nasty stuff to happen. Plus the a/c cycle (system) will operate more efficiently without air in it. You need a set of AC manifold gauges. You can get a cheap set for around 50 bucks. The better sets are a little more, but worth it since the fittings are better. You need to pull a deep vacuum, ~29.99 in/Hg for about 30 min. Then you start charging the system with refrigerent. Start pressurizing with the system off. Once the pressure in the can equalizes with the system, start the car and run the ac system. make sure to only have the low pressure suction side open....and keep the can facing upright so you don't draw liquid into the compressor. I'd really recommend taking the car to someone to have this done if you don't have any ac experience. It "should" be cheaper to have someone do it, than buying all the equipment to do it right. Quote Link to comment Share on other sites More sharing options...
nipper Posted May 12, 2009 Share Posted May 12, 2009 I'd really recommend taking the car to someone to have this done if you don't have any ac experience. It "should" be cheaper to have someone do it, than buying all the equipment to do it right. And safer. nipper Quote Link to comment Share on other sites More sharing options...
idosubaru Posted May 12, 2009 Share Posted May 12, 2009 A vacuum boils the water out of the system, removes air/contamination, etc. That being said, I've charged countless cars without pulling a vacuum. It's easy and works a very high percentage of the time (i'm still batting 1000). My friends Honda civic was blowing 42 degrees after replacing the compressor, that was about 5 years ago and he's still running it just fine. I even had a vacuum puller but he was too lazy too wait. It's really easy. Subaru's take about 2 cans when fully emptied. The ghetto way my HVAC licensed cousin said to do it was to pressurize through one side and keep the valve open on the other...thereby forcing some stuff out just by the pressure of the can. I don't ever do that though. Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted May 12, 2009 Share Posted May 12, 2009 (edited) Right the vacuum does at least two things, one it gets the air out of the system so it can run most efficiently, and second, if you have a high enough vacuum (higher than the air compressor driven units can create), and a high enough ambient temp, you can get the water in the system to boil and then be drawn out of the system through the vacuum pump. But you need a very strong vacuum, then the water will boil as low as maybe 60 deg. F., and then draw it for a long enough period of time for it to travel to the vacuum pump. If the system had a leak for a long time and was never recharged some people like to replace the drier to get fresh dessicant. Edited May 12, 2009 by porcupine73 at least Quote Link to comment Share on other sites More sharing options...
nipper Posted May 12, 2009 Share Posted May 12, 2009 Right the vacuum does two things, one it gets the air out of the system so it can run most efficiently, and second, if you have a high enough vacuum (higher than the air compressor driven units can create), and a high enough ambient temp, you can get the water in the system to boil and then be drawn out of the system through the vacuum pump. But you need a very strong vacuum, then the water will boil as low as maybe 60 deg. F., and then draw it for a long enough period of time for it to travel to the vacuum pump. If the system had a leak for a long time and was never recharged some people like to replace the drier to get fresh dessicant. It does a third too. It will tell you if you have a leak, as it wont pull down a proper vacume. nipper Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted May 12, 2009 Share Posted May 12, 2009 It does a third too. It will tell you if you have a leak, as it wont pull down a proper vacume. Excellent, thanks, post corrected Quote Link to comment Share on other sites More sharing options...
bgambino Posted May 12, 2009 Author Share Posted May 12, 2009 The ghetto way my HVAC licensed cousin said to do it was to pressurize through one side and keep the valve open on the other...thereby forcing some stuff out just by the pressure of the can. I don't ever do that though. Gary I like this idea thanks! Quote Link to comment Share on other sites More sharing options...
idosubaru Posted May 13, 2009 Share Posted May 13, 2009 GaryI like this idea thanks! cool, let me know how it turns out. like i said, i never tried it and don't know if it's applicable to automotive systems or subarus. i'm just passing along what he said. the good news is that i've never had a problem, even without doing anything, so if it helps at all you're one step ahead of me and i've never had a glitch. trying that "trick" or getting new dessicant i think would the best move. Quote Link to comment Share on other sites More sharing options...
ScottG Posted May 13, 2009 Share Posted May 13, 2009 Another way to pull a vacuum is to use the engine of your Subie. Connect a 'T' in one of the vacuum lines (below the throttle plate) & hook that to your low side gauge. It will pull about 29 inches of mercury in 5 minutes or less. As has been already posted, the vacuum should be pulled for at least a half hour (I generally go for 45 to 60 minutes). Anyway, this method eliminates the need for a special vacuum pump & I think it's a really neat way of doing things. A few years ago, I found a Mercury dealership in my hometown using this method when replacing AC compressors, driers, leaky lines, etc. ScottG Quote Link to comment Share on other sites More sharing options...
idosubaru Posted May 13, 2009 Share Posted May 13, 2009 wow, that is a very interesting way to do it. sounds like it'd be really annoying customizing the fittings to go from a standard vacuum hose to the a/c gauge fittings. whatever is in the a/c lines is going to end up in the gauges and engine. just a thought, probably not a big deal. i've had oil in cylinders foul my compression gauges. Quote Link to comment Share on other sites More sharing options...
1-3-2-4 Posted May 24, 2009 Share Posted May 24, 2009 If it has not been said don't forget to add oil to the system as well. Quote Link to comment Share on other sites More sharing options...
Scoobywagon Posted May 24, 2009 Share Posted May 24, 2009 Another reason to pull a vaccuum prior to charging is that R134a is corrosive in the presence of air. The problem with that is that your evaporator core is usually made of relatively thin aluminum that will corrode in a few years. You end up with a bunch of pin holes in the evap core and wasting a lot of refrigerant. And, just so I can say I said so...Venting refrigerant into the atmosphere is a VERY bad idea....environmentally speaking. People have paid HEAVY fines for that. Just so you know. Quote Link to comment Share on other sites More sharing options...
1-3-2-4 Posted May 25, 2009 Share Posted May 25, 2009 Another reason to pull a vaccuum prior to charging is that R134a is corrosive in the presence of air. The problem with that is that your evaporator core is usually made of relatively thin aluminum that will corrode in a few years. You end up with a bunch of pin holes in the evap core and wasting a lot of refrigerant. And, just so I can say I said so...Venting refrigerant into the atmosphere is a VERY bad idea....environmentally speaking. People have paid HEAVY fines for that. Just so you know. question.. I'm guessing the best way is using uv die but the evaporator can just go belly up on it's own? i found a load of leaves and pinestraw which was about 3 inches deep where the evaporator is.. cleaned it all out but still have poor cooling.. I notice when I turn on the AC now I hear a slight hiss from the area sounds like the expansion valve. having said that I plan on getting some Manifold Gauges and I was looking at a vacuum pump it is rated for 75 micron/10 Pascal. Quote Link to comment Share on other sites More sharing options...
Scoobywagon Posted May 25, 2009 Share Posted May 25, 2009 Just so we're clear.... The evaporator is in the dash, the condenser is under the hood. Just want to make sure we're talking about the same parts here. Hearing a bit of a hiss from the system is not unheard of. The expansion valve and reciever/drier both make some hissing noises. As far as having the evaporator fail, yes it can fail "on its own". Its just aluminum, and usually fairly thin aluminum at that. Being soft, it won't take a lot of abuse and corrosion is DEFINITELY not your friend here. The thing to do is to pull it down to as hard a vaccuum as you can and make sure that the system will hold that. In our shop, the vehicle sits for a MINIMUM of 30-45 minutes. If the guage shows full vaccuum, you're good to go. Otherwise, its time to track down a leak if that needle has moved AT ALL. The pump we use is this one. Pull it down to vaccuum, make sure it holds that vaccuum, add refrigerant to fill. The sight glass in the reciever drier is USELESS for this. Check your service manual for refrigerant capacity. Most vehicles are in the 2-2.5 lb range. Good luck! question.. I'm guessing the best way is using uv die but the evaporator can just go belly up on it's own? i found a load of leaves and pinestraw which was about 3 inches deep where the evaporator is.. cleaned it all out but still have poor cooling.. I notice when I turn on the AC now I hear a slight hiss from the area sounds like the expansion valve. having said that I plan on getting some Manifold Gauges and I was looking at a vacuum pump it is rated for 75 micron/10 Pascal. Quote Link to comment Share on other sites More sharing options...
1-3-2-4 Posted May 25, 2009 Share Posted May 25, 2009 yep I know where the evaporator is.. I just cleaned about 4 inches worth of pinestraw and leaves from the airbox.. it was blocking the whole evaporator. I don't have my gauge set yet but I'm about to go out now to check if I see any oily deposits around any of the fittings. I hear the most common leaking area is the o-rings on the compressor. my compressor is a Zyxel. also yes the factory service manual really helps. *edit* What did you use for compressor oil? Quote Link to comment Share on other sites More sharing options...
Scoobywagon Posted May 25, 2009 Share Posted May 25, 2009 Most refrigerants come with compressor oil in them. The oil is just mineral oil, but you'll have to work out just how much you need. Quote Link to comment Share on other sites More sharing options...
1-3-2-4 Posted May 25, 2009 Share Posted May 25, 2009 yeah I have to check the FSM again to see how much is needed. while I was under the car I also checked out the condenser it's got road grime on the passenger side of it and driver's side as soon as my gauges come I will be checking the pressure. Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted May 26, 2009 Share Posted May 26, 2009 Mineral oil was for R12 systems. R134A generally uses PAG. The zexel and calsonic took different weights one was 100 I htink the ohter was 110. Quote Link to comment Share on other sites More sharing options...
myhilo Posted June 3, 2009 Share Posted June 3, 2009 I've done as Legacy777's post mentions, I have the gauges, vacuum pump installed as my current post as of today mentions. BUT I can't get the compressor to engage, how is it wired, can't find enough info to locate or bypass a pressure sensor, can I directly engage the compressor clutch? myhilo Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted June 3, 2009 Share Posted June 3, 2009 How much pressure do you have in the system? Quote Link to comment Share on other sites More sharing options...
Scoobywagon Posted June 3, 2009 Share Posted June 3, 2009 The compressor will not run without proper pressure in the system. This helps prevent it from eating itself in the event of a leak. Why are you trying to the compressor with a vacuum pump on? Quote Link to comment Share on other sites More sharing options...
ScottG Posted June 3, 2009 Share Posted June 3, 2009 Generally, the procedure is to make the repairs (replace compressor, 'O' rings, condenser, leaky lines, etc). Then, after the system is completely back together & all the fittings & bolts are tightened to specification, connect the vacuum pump to your gauge set. Draw a vacuum for a minimum of 30 minutes (I like to get every bit of corrosive moisture & air out of the system, so I generally vacuum for 45 minutes to an hour). Then, as has already been posted, let the vehicle sit for an hour or so with the vacuum pump off. The purpose of this exercise is to see if the system has any leaks. As has been posted, if the vacuum gauge shows any loss over this period, you must go back & find the leak that exists. If you put R-134 in a system that won't hold a vacuum, you are wasting your time & money, for the refrigerant will be gone overnight and you will have permitted it to escape into the atmosphere - not a nice thing to do to the environment...and VERY illegal. If the system holds a vacuum, close the low side (blue)valve on the gauge set & hook up a can of R-134 refrigerant. Without running the engine, inject as much refrigerant as you can (until the pressure in the can & the presure in the system are fairly equal). This usually provides enough pressure for the compressor to run without beating itself to death because of too little pressure. As has been posted already Do Not run the compressor while the system is in vacuum, or when there is no pressure in the system. Most new generation Subies take around 23 ounces (plus or minus an ounce or 2)of refrigerant. There should be a label on the radiator support that shows the exact amount. Now, start the car, engage the compressor, place the AC contol on RECIRC & turn the blower fan to full speed. Keep adding refrigerant until the can is empty. Close the low (blue) side valve on your manifold gauge set. Attach a second can to rplace the empty one you just removed. Add refrigerant until you have injected the amount specified on the refrigerant sticker. Disconnect the manifld gauge set & you're done. Wear safety glasses & keep the fittings on the refrigerant can & the gauges away from your face. Leaking refrigeant contacting skin will give you frostbite. Work safely.....Keep Kool ScottG Quote Link to comment Share on other sites More sharing options...
myhilo Posted June 4, 2009 Share Posted June 4, 2009 Thanks for the advise guys. I was not trying to run the compressor with the vacuum connected. I had connected the vacuum pump as suggested to evacuate the system, It immediately brought the low side gauge to full vacuum, I let it run for about an hour. I then disconnedted the vacuum pump, by removing the center yellow hose from the vacuum pump and attaching it to the center secondary fitting on my gauge set. I then opened the low and high side quick connect valves and the low and high side gauge valves. there was a quick sucking of the yellow hose air from disconnecting it and then the vacuum stayed at greater than 29mm Hg for at least 30 minutes. This told me there was no large leak. I then connected a 134a container which weighed 17.40 oz with the fitting and after opening the can (which was upright) and the gauge high and low valves and the quick connect valves the system began to fill. The 134a container began to cool, I had about 40 psi I think the filling soon slowed, and after about 30 minutes I knew no more was transferring. I then closed the high side quick connect valve and the high side gauge valve. I have my assistant start the car and turn on the A/C. I expect the compressor clutch to then kick in and the compressor would then aid in the rest of the system fill. HOWEVER, the evil compressor will not engage, so I can fill the system any further. My questions now: Is there a pressure sensor or switch somewhere which is falsely preventing the compressor clutch from being engaged? Can I jumper the single wire leading to the compressor to 12VDC to cause the compressor to run? I would like to at least acheive a complete fillning so I know the rest of the system is functioning and can cool the car. I can then track down the continuing fault(s) pressure switch, or bad wire or A/C compressor relay? P.S. It would help if I could find a complete schematic showing the A/C system components and locations. I only have the Chilton's total care for a range of cars of this period and it doesn't show any A/C stuff. Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted June 4, 2009 Share Posted June 4, 2009 Maybe I missed it, but what year and model subaru do you have? Quote Link to comment Share on other sites More sharing options...
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