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Old 04-24-2012, 11:32 PM   #1
Scooby Specialist
Member#: 121459
Join Date: Jul 2006
Chapter/Region: BAIC
Location: San Francisco, CA
2002 WRX

Default A/C low line pressure did not rise after system recharge?

Today I decided to try out one of those over the counter A/C recharge cans on our Forester & Impreza. I started with the Forester, as it was already warmed up. According to the chart on the back of the can, due to it being 80 outside, the low pressure side of the system should have been between 40 & 50 psi with the car warmed up & A/C blasting on high, making sure the compressor clutch is engaged. Well, following all that, the pressure in the system came up at about 26 psi. Great! I thought, I didn't just needlessly spend $35 dollars on this recharge can! Well, My original plan was to recharge both cars with one can, so I purchased a larger 22oz can. I followed the directions to a T, tilting the can between 12:00 & 3:00 positions & shaking every few seconds. I ended up dumping the whole can into the Forester & the pressure just stayed at 26 psi.... What gives?? If there were a leak, it shouldn't hold steady at 26, but if it took the entire contents of the can, why did the pressure stay the same?

After the can was gone, I warmed up the WRX & checked it's low pressure line w/ the gauge that came with the can & it ALSO measured at 26 psi...... Is there some sort of pressure threshold on our cars that I'm not aware of? Is it just coincidence that both cars read the same pressure & they are both low? I"m pretty sure it's not a fault of the gauge itself, as when the compressor would periodically turn off on the WRX, & the pressure would equalize with the high side, it would read up near 55 psi. As soon as the compressor came on, back down to 26. Any info on this would be a huge help! Need to get ready for our first summer in Texas!!

Edit: I should add, that even though the pressure did not seem to go up in the Forester's A/C system, it did seem to blow noticeably colder than it did before.... So I guess that's good?

Last edited by silence2-38554; 04-24-2012 at 11:37 PM. Reason: More info
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Old 04-25-2012, 01:12 AM   #2
Scooby Newbie
Member#: 242868
Join Date: Apr 2010
Chapter/Region: BAIC
Location: NorCal
1998 Legacy
EJ205 - Silver


Was your AC working before you added the freon?

I once had a leak from the high line into the compressor, I changed the o-ring, vacuumed it and re-added freon and has been working for almost a year now.

There could be a leak in your system. On mine, I tried refilling it, it worked for a day, and then stopped. My friend noticed small bubbles from where the leak was.

1) The gauges on the AC cans are not that accurate, but can be used as a rough guide. AC gauge manifold is the more accurate option.
2) There may not be enough freon in your system. I say that because your compressor periodically shuts off, and the pressure is not up to range, yet. From what I observed before when re-filling freon, is that the compressor shuts off if the pressure gets too low, until enough freon goes in, for the compressor to work with.
3)There may be a leak in your system. You can use the UV leak detect stuff, some may come with freon. A lot of people are against the stop leak

That being said, if your AC works throughout the season, you should be fine.

I believe my low side pressure was around 38-40psi at around 75 degree temperature after it was filled with the AC on, and I think it took 2-12oz cans (I'm not sure if I opened a 3rd can).

I briefly looked into the 1998 Legacy Service Manual and it said to keep the pressure below 40psi, btw, I'm not sure about your Forester or WRX. I hope all this helps, and your ACs blow cold!
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Old 04-25-2012, 03:33 PM   #3
Scooby Specialist
Member#: 121459
Join Date: Jul 2006
Chapter/Region: BAIC
Location: San Francisco, CA
2002 WRX


Yeah, the AC was working, it just took a while to get cold & once warmed up it was "cool" but not really cold. Been like that for about a month. Since the compressor shutting on & off is not normal behavior (I thought it was!) on the WRX, I might go pick up another can today & see what the pressure does when adding it to that car, compared to the Forester. Also, good to know about the 40psi spec in the Legacy manual!
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Old 04-25-2012, 04:14 PM   #4
Scooby Specialist
Member#: 132389
Join Date: Nov 2006
Chapter/Region: BAIC
Location: SF Bay Area
2006 WRX Wagon SGM
2003 SV1000S, 2014 DL650


Originally Posted by Tolew45 View Post
1) The gauges on the AC cans are not that accurate, but can be used as a rough guide. AC gauge manifold is the more accurate option [...]
Agreed. A manifold gauge set is the only correct way to assess the situation with an A/C system. Both low and high pressures need to be checked (the low pressure may look OK while the high pressure could be completely off).
Fortunately, manifold gauge sets are not very expensive. I'd suggest buying one before randomly refilling the system with cans of freon.
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Old 04-25-2012, 07:41 PM   #5
Scooby Newbie
Member#: 316307
Join Date: Apr 2012
Chapter/Region: South East
Location: Kannapolis, NC
2002 Impreza WRX


Like the others said, a set of manifold gauges would be significantly better than what comes with the can of refrigerant. Whatever you do, don't buy any stop leak or "miracles in a can" because it's only going to give you a bigger headache than you had with a leak in the system.

On the WRX, I wouldn't be surprised if your leak is coming from the o-rings where the lines meet the compressor. Super common problem I have seen on these cars. Hopefully that's the case and you wont' need to buy a $500 compressor
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