A/C Question

Joined
Jun 10, 2005
Messages
200
Location
Atlanta
I have a 1991, all original, with R12. My Ac dryer was leaking from the viewport seal, bubbling slowly. I got a new dryer. I evacuated the system, and left the gauges on over the weekend and the pressure kept at -30inHG. Now a yearish later, the a/c has lost pressure again. It still had some pressure in it but not enough to turn on the compressor. I evacuated again, on Monday, now on Thursday it is still holding again at -30inGH. Should I leave it on for a few more days? I guess my question is, Can an O ring hold pressure at negative and somehow lose pressure at positive when the system is pressurized?
 
Joined
Mar 20, 2004
Messages
511
Location
tarrytown,n.y.
Yes , the system can leak on pressure and not on vacuum . Is not very common but i have dealt with this before , the culprit i found was the compressor seal . I have also seen on older cars or cars that get seldom use these type of problems come up from dried o rings . They seal on vacuum and leak very slightly on pressure . I try to drive my car every weekend as long as there is no salt on roads , before put in garage i run the defroster(brings on compressor ) for about 10 minutes . when you pull the system to a vacuum watch the gauge as it approaches -26 HG, this is the vacuum when water will boil off , if the needle starts bounce or hesitates ,you got moisture . In my a/c classes I use to introduce water to a system to show the students what it would look like
 
Joined
Jun 1, 2005
Messages
746
Location
Switzerland
Yes. Total vacuum is only 1 bar difference. While on pressure your ac system is around 2.5 bars at low pressure side and 4 times more at high pressure side. Fill your system and try to detect the leak on pressure, either with UV dye or by soap bubbles. Pray the leak is not at the evaporator. Personally, I had the valve at the low pressure side that was leaking.
 
Joined
Mar 20, 2004
Messages
511
Location
tarrytown,n.y.
Yes. Total vacuum is only 1 bar difference. While on pressure your ac system is around 2.5 bars at low pressure side and 4 times more at high pressure side. Fill your system and try to detect the leak on pressure, either with UV dye or by soap bubbles. Pray the leak is not at the evaporator. Personally, I had the valve at the low pressure side that was leaking.

I didnt even want to mention the evaporator , check some of the easier things first , then put the sniffer in a/c outlet and yes pray its not there
 
Joined
Jun 10, 2005
Messages
200
Location
Atlanta
Thanks guys! I just couldnt wrap my head around an o-ring acting like a one way valve. Cinco de Mayo didnt help much either. I have the dye and will try it. As for the pressure, it always had pressure in it, just not a lot. Needle goes to -30 in about 1 minute with no hesitation. I actually had the high side valve leaking without me knowing it when I changed the dryer. Out of pure luck, I was sweating a lot, and sweat hit the valve before I capped it. It started bubbling, I was already frustrated/angry when I saw that, a complete calm came over me and I thanked the NSX Gods. I would have never found that. I assume this is right, put just a little of the dye in 1/2 oz, and enough freon in to start the compressor, and start looking?

Thanks again and have a great weekend,

Dean
 
Joined
Mar 20, 2004
Messages
511
Location
tarrytown,n.y.
When you remove gauges you have to blip(just tap needle on valve) the schrader valves on high and low side . Always check for leak at valves to make sure they seated. you can buy a tool tool to change the schrader valves while under pressure , so you dont have to drain system . Hopefully everything works out .
 
Joined
Jun 10, 2005
Messages
200
Location
Atlanta
Quote Originally Posted by 2-Saw
Quote Originally Posted by ralph cerbone
Quote Originally Posted by 2-Saw
Hey,

I appreciate all your help with the A/C. Are you 100% the schrater valve is removeable on the NSX? I have the tool and extra valves. I remember some thread where a guy said you had to replace that part of the line. Just double checking.

Thanks,

Dean
Hey Dean ,my car is a 97 and yes they are replaceable , if you look up the parts you will see they are replaceable . Iam sorry I didnt mention it in the post but after 50 yrs of servicing a/c i just check every time i disconnect gauges ,dont even think about it . I always blip the the valve .

Ralph,

Thanks again for the info. That "blip the valve " thing was a real eye opener. I got lucky.
 
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