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  #1  
Old 12-20-2006, 04:20 PM
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A/C normal pressure in low and high lines.

How many psi A/C has to get in lower and higher lines (when +70F outside)?

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Old 12-20-2006, 06:04 PM
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When I did my AC last summer, it was 35-45 mmHG on low side and 175-190 mm Hg on the high side with the AC manifold guages. It also depend if you are using R12 vs. R 134. I remmember R134 runs a little higher.

John
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Old 12-20-2006, 06:22 PM
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Opps. Sorry. The car is W210 E320 wagon. A/C keeps R134A.
Why I'm asking about it. A few days ago I created topic about green pool, which I found out under car (Green stuff under car). On last Saturday I checked the low pressure in A/C. It was 30 psi. I guess that it is not too low. But... How it could happen?! So much oil was blew out (I guess at least 10..20ml), but A/C still under high pressure?!
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  #4  
Old 12-20-2006, 06:36 PM
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Ac

You need to borrow the R134 Ac manifold from autozone and check the pressure with AC running. If you are checking the low side w/o AC on, the static pressure seems low, mine was in the 60-70 mmHg with R12. If the pressures are ok. I would look for leaks in the system. Hopefully, all you need is to tighten up the hose line. If the pressures are low all around, then you will have to evacuate the system at a shop, then replace the leaky hose, install new r134 compatible o-ring, vacuum, and recharge the system. You must know the hi/lo pressure before working on the above.

John
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Old 12-20-2006, 06:39 PM
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Ac

Also, with ac system, even with low freon, it still can generate quite a bit of pressure, that's why you need to have accurate hi/lo pressure to diagnose the problem. 10-20 ml loss is not that much, less than one ounce.

John
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  #6  
Old 12-20-2006, 07:18 PM
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Quote:
Originally Posted by pexcellence View Post
When I did my AC last summer, it was 35-45 mmHG on low side and 175-190 mm Hg on the high side with the AC manifold guages. It also depend if you are using R12 vs. R 134. I remmember R134 runs a little higher.

John
You do realize that 1 PSI = 51.7 mmHG, right ???????????
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Old 12-20-2006, 09:40 PM
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Question

What is OEM specification on it? I cannot find it at WIS I just found that refrigerant (R134) capacity is 1 liter. That is it...
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  #8  
Old 12-20-2006, 11:04 PM
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Pressure can vary quite a bit depending on ambient temp and engine RPM. You will need to calculate using a pressure/temp chart; do a search and you will find one either here or elsewhere on the Internet. The best way to charge is to evacuate completely and charge by weight. Do a search here - a capacity chart was posted.
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Old 12-20-2006, 11:23 PM
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Oh, one more thing - if you do decide to evacuate you need to be sure to monitor for and replenish any oil that is lost, typically a couple ounces.
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Old 12-23-2006, 10:33 PM
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The pressure I quoted was in metric (mm Hg). If it is a liter of R134, then roughly, it should be about 33 ounces.

If you meant 30 mm Hg (not psi) on the low side with the engine running and AC on, you may be a little low on refrigerant. You still need to check the high side also to see if you are getting low pressure. Otherwise, you may overcharge the system, if you decide to add more r134.

John
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  #11  
Old 12-26-2006, 12:23 AM
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Somehow the sight glass at the dryer had a crack

Somehow the sight glass at the dryer had a crack (1995 280 C) and all the refrigerant escaped so I just replaced the dryer with a new unit and added 2 cans of r134 it worked fine for about 3 days now the a/c only works at freeway speeds (very cold) but at idle and at City driving itís not cold at all, I open the hood and I can see thru the glass the r134 is not circulating, I can see the dryer full of r134 but it looks still until I rev up the engine but then the flow stops completely for a few seconds and then it starts circulating again, any idea why is this happening?
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Old 12-26-2006, 02:42 AM
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<>

The pressure you quoted was in PSI.
Not mm of mercury.
..and metric conversion for PSI on a/c systems is in BARS, not mmHG..
Do the math..

Last edited by Arthur Dalton; 12-26-2006 at 02:54 AM.
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  #13  
Old 12-26-2006, 11:49 PM
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Do not rely on the sight glass on a converted R134A system as it's practically worthless for anything other than seeing if there is general flow. Newer R134A systems don't even have a sight glass. Proper charge is achieved by weight. If the system is cycling excessively, it may be overcharged and causing the high-pressure cutout switch to disengage the compressor periodically.

You really need to provide more info. Can you tell us where you are located? Climate? Ambient temps with related manifold pressures? Have you looked into the pressure/temp chart as suggested earlier?

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