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Over 48 hours, Vacuum dropped from 29.5 to 28.5 in-Hg

nyc951 on Fri August 24, 2007 9:11 PM User is offline

Year: 1993
Make: Lexus
Model: SC400

Hi:

I know the a/c system probably has a leak, but I'm in denial b/c I spent hours fixing it this week. Besides a leak in the system, would something else cause the disparity in the readings? The same gauges were used.

Oh, when I checked today, I only attached the Low Side hose. Would connecting the High Side as well make a difference in the readings?

Thanks.

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'98 328i

TRB on Fri August 24, 2007 9:38 PM User is offlineView users profile

Charge the system!!!

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
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nyc951 on Fri August 24, 2007 9:47 PM User is offline

Tim:

Are you saying the system should be good to go even though it dropped by 1 Hg? Don't want to waste the R12!

Or should I charge with 134a and see if it holds?

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'98 328i

Chick on Fri August 24, 2007 9:48 PM User is offlineView users profile

A simple change in temperture, amoung other things, could cause that after 48 hours.. I agree, pull it down again and charge the system....Let us know what happens...

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Cussboy on Fri August 24, 2007 9:56 PM User is offline

You got a tiny bit of air in it when you re-connected the hoses/fittings, analogous to the brief spit of refrigerant that would leak out had the system contained refrigerant. So I agree with the others, don't be so anal about this: pull good vacuum, and charge with proper amount of refrigerant. Even if you had NOT disconnected and reconnected the hoses, such a small change would be insignificant.

nyc951 on Fri August 24, 2007 10:18 PM User is offline

Quote
Originally posted by: Chick
A simple change in temperture, amoung other things, could cause that after 48 hours.. I agree, pull it down again and charge the system....Let us know what happens...

A simple change in temperture

Hmm, when I did the repairs and pulled the vacuum a couple of days ago, it was about 72 degrees out and not humid. Tonight, it is humid, and the car was just driven so the engine bay was HOT. Out of curiosity - Would a rise in temps cause the drop in vacuum? (Should know this from college thermodynamics - shame on me)

Ok, I'll pull a vacuum and report back.

Thanks all.

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'98 328i

TRB on Fri August 24, 2007 10:37 PM User is offlineView users profile

When we check to see if a system is holding a vacuum it is like for 10 minutes. The variables in your 48 hours test are too many to list. My suggestion is charge it and leak check it with an electronic or UV detection device.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Ralliart16 on Fri August 24, 2007 11:02 PM User is offline

I wouldn't worry about that at all!

For my car (Saturn), the Factory service manual specifies that anything less than 1" drop within 5 minutes is acceptable.

hjc149 on Sat August 25, 2007 2:33 PM User is offlineView users profile

I usually leave my gauges hooked up after pump down overnight. If the system is tight, I've never seen a drop in reading. IMO a drop of 1" in 5 minutes would indicate a pretty good leak somewhere.

nyc951 on Wed August 29, 2007 12:25 PM User is offline

Quote
Originally posted by: TRB
Charge the system!!!


Success! (for now, knock on wood)

It's been a week today since I pulled a vacuum and the system still held the vacuum to within .5 inHg. As you guys mentioned, when I hooked up the gauges to the fittings on the car the readings were affected.

So I charged about 36 ozs of R-12 and got pressures to ~200psi and ~20psi at around 2000 rpm. I lost a bit of refridgerant when I disconnected the gauges - I was surprised by how much came out but I guess it's normal when you consider the pressures involved. The ambient temp is around 85, but with the car sitting in the sun, it's probably more than that. Driving around town in recirculation mode, the vent temps were around 43 degrees and in fresh air mode about 45 degress. This is city driving.

So thanks to you guys for helping me get over my paranoia! I checked with an electronic sniffer and the a/c system seems tight like a drum

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'98 328i

Edited: Wed August 29, 2007 at 12:28 PM by nyc951

NickD on Wed August 29, 2007 12:44 PM User is offline

AirLift airbags spring assists expected weak me to roll up their bags and jammed them in a tiny 2" diameter hole by hand. Called them said leave them out in the sun, said I already put them in my chamber and heated them to 165*F, still no luck. So I installed brand new Scharder tire valves, jury rigged a tire chuck to my vacuum pump and really sucked out the air. Clever? But as soon as I removed the chuck air started leaking back into this bags, vacuum was pulling the Scharder valve open, had to quickly install the cap.

This is a flexible bag and not a hard device like an AC system, point is that AC systems are not designed to hold a vacuum, but to hold pressure, compressor seals are notorious for pulling in and sucking air. With your gauges installed, barometric pressure variations are key in your actual vacuum reading.

You are not the only one cautious and no longer dealing with a 75 cent can of R-12. To be cautious, would connect the blue line to the pump, yellow to a closed off can, red to the high side. Open the low side, draw a deep vacuum to the open high side and also way down to the can's valve, close off the low side and dump just one can in. Remove the gauges, then check for leaks, only sacrificing one can and with pressure, better to have a little R-12 leak out than air being sucked back in, so can finish off the charge from there, purging with each added can. Well, that is why I like the tanks, saves all that purging.

But hopefully, all is well that ends well.

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