My AC Gauge Reads -100 on Vacuum - Team Camaro Tech
Heating & Cooling Heating, cooling and air conditioning

 
LinkBack Thread Tools Display Modes
post #1 of 13 (permalink) Old Jul 9th, 11, 02:48 PM Thread Starter
Senior Tech
 
Join Date: Aug 2001
Location: Dallas, Texas
Posts: 847
My AC Gauge Reads -100 on Vacuum

Okay good people. Iím brand new at this & have been reading & reading about various aspects of the old R12 ac system lately.

I went & got an AC vacuum pump at the store for about $100.00 today.

I hooked up the blue to the low side POA valve & the red to the outlet on the compressorís muffler (both look & work kind of like an inter-tube valve).

The blue low side gauge goes down to -100 & sits there very stable.

I turned the pump off after about ten minutes of use.

The low side still just sits rock solid at -100.

IS THIS A PRETTY GOOD INDICATION I DONíT HAVE ANY LEAKS IN MY SYSTEM?

I would like to fill the system with 200psi of nitrogen (like I've read about) but I donít really have access to nitrogen.

I called a local welding shop & he wanted like $170.00 for the smallest quantity they sell.
327!275hp!Convt! is offline  
Sponsored Links
Advertisement
 
post #2 of 13 (permalink) Old Jul 9th, 11, 03:08 PM
Gold Lifetime Member
scott
 
68basecoupe's Avatar
 
Join Date: Aug 2009
Location: millbrook,al.
Posts: 466
Re: My AC Gauge Reads -100 on Vacuum

If it holds a vacuum then ther are no leaks,if you decide to pressure test the system with dry nitrogen you will still need to pull a vacuum to around 50 microns before you charge the system to make sure there are no non condenseables in the system.
68basecoupe is offline  
post #3 of 13 (permalink) Old Jul 9th, 11, 06:28 PM
Senior Tech
 
Join Date: Jul 2005
Location: California
Posts: 2,353
Re: My AC Gauge Reads -100 on Vacuum

You need to let it sit under vacuum for an extended period of time to ensure no leaks. We like to go 1 hour at work. The longer the better and more sure you can be that there are no leaks.

But, what units are you using that the vacuum reaches 100?
400bird is offline  
 
post #4 of 13 (permalink) Old Jul 9th, 11, 08:10 PM Thread Starter
Senior Tech
 
Join Date: Aug 2001
Location: Dallas, Texas
Posts: 847
Re: My AC Gauge Reads -100 on Vacuum

Quote:
Originally Posted by 400bird View Post
You need to let it sit under vacuum for an extended period of time to ensure no leaks. We like to go 1 hour at work. The longer the better and more sure you can be that there are no leaks.

But, what units are you using that the vacuum reaches 100?
I think my a/c gauges were pretty low end in price. They say Imperial USA. On the low (blue) side the numbers are colored green that go into the negative digits, below zero. Right after the green negative numbers in very fine print it says "in Hg vac." The negative numbers go down to -100 on the dial.

It is 10pm now. The gauge readings have not moved in the slightest since about 3:30 this afternoon. I have read they should be in the same position for 24 hours if there isn't a leak, but that's with 200 psi of nitrogen. I am only holding a vacuum from the vacuum pump.
327!275hp!Convt! is offline  
post #5 of 13 (permalink) Old Jul 9th, 11, 08:43 PM
Senior Tech
JAY
 
Join Date: Jul 2009
Location: TUCSON AZ
Posts: 726
Re: My AC Gauge Reads -100 on Vacuum

Greetings from Arizona
Charge the system with r12 and add dye. If it held vacumn that long you don't have any issues. VERY small leaks might show up. I charged my 67 after about 1 hour under vacumn. no leaks but found POA valve wasn't working. I wanted to retain stock ac look, POA valves are no longer made or rebuilt. Found local ac shop that had access to POA Valves that have been cut in half, machined out, and new orfice tube installed internally. looks stock but looks 100% orginal. Jay


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

66 SS Chevyll
67 Elcamino
68 Malibu 2dr
69 Camaro Convertible
JAYARTER is offline  
post #6 of 13 (permalink) Old Jul 9th, 11, 09:02 PM Thread Starter
Senior Tech
 
Join Date: Aug 2001
Location: Dallas, Texas
Posts: 847
Re: My AC Gauge Reads -100 on Vacuum

Quote:
Originally Posted by JAYARTER View Post
Greetings from Arizona
Charge the system with r12 and add dye. If it held vacumn that long you don't have any issues. VERY small leaks might show up. I charged my 67 after about 1 hour under vacumn. no leaks but found POA valve wasn't working. I wanted to retain stock ac look, POA valves are no longer made or rebuilt. Found local ac shop that had access to POA Valves that have been cut in half, machined out, and new orfice tube installed internally. looks stock but looks 100% orginal. Jay
I tested the POA with gauges & air compressor before putting everything back together. The gauge kept a steady reading of right about 29 like the instructions said it should.

Why should I add dye? What kind? What does that do? Do you add it at the sametime you add the oil to the compressor?
327!275hp!Convt! is offline  
post #7 of 13 (permalink) Old Jul 10th, 11, 11:59 PM
Senior Tech
John
 
Join Date: Feb 2004
Location: Bloomingdale, Il
Posts: 507
Re: My AC Gauge Reads -100 on Vacuum

Dye is used to pinpoint tiny leaks in a running system It is sold in small 1-2oz charges and is added thru low press port same way the system is charged. A leak will show up with a UV light. It can be useful in detecting a slowly leaking evaperator or condensor coil.

You really should check the system under high pressure (after all, it operates under pressure, not vacuum.) Vacuum testing will indicate big leaks right away. High pressure Nitrogen will show a small leak over a longer period of time, say overnight but the longer the better. Use Snoop, or LeakCheck, or whatever popular leak detection liquids to check all fittings or suspect flanges. FWIW, I have seen systems that would hold a vacuum, but not pressure.

Call a local hvac shop. They may charge you up with dry Nitrogen for a few bucks since you already have pulled a vacuum.

btw... Like everyone else has said... You want to pull a DEEP vacuum for an hour or more to insure ALL moisture is removed. 10 min simply isn't long enough. Some techs say 30 min or so vacuum pumping is ok, but if it's humid when the system is open, overnight sure won't hurt! .....Jb

.

Beat it to Fit, Paint it to Match!

Last edited by Johnny B; Jul 11th, 11 at 12:17 AM.
Johnny B is offline  
post #8 of 13 (permalink) Old Jul 11th, 11, 05:02 AM
Gold Lifetime Member
Mike
 
prostreet69camaro's Avatar
 
Join Date: Jul 2003
Location: Spring Texas
Posts: 5,580
Re: My AC Gauge Reads -100 on Vacuum

Quote:
Originally Posted by Johnny B View Post
Dye is used to pinpoint tiny leaks in a running system It is sold in small 1-2oz charges and is added thru low press port same way the system is charged. A leak will show up with a UV light. It can be useful in detecting a slowly leaking evaperator or condensor coil.

You really should check the system under high pressure (after all, it operates under pressure, not vacuum.) Vacuum testing will indicate big leaks right away. High pressure Nitrogen will show a small leak over a longer period of time, say overnight but the longer the better. Use Snoop, or LeakCheck, or whatever popular leak detection liquids to check all fittings or suspect flanges. FWIW, I have seen systems that would hold a vacuum, but not pressure.

Call a local hvac shop. They may charge you up with dry Nitrogen for a few bucks since you already have pulled a vacuum.

btw... Like everyone else has said... You want to pull a DEEP vacuum for an hour or more to insure ALL moisture is removed. 10 min simply isn't long enough. Some techs say 30 min or so vacuum pumping is ok, but if it's humid when the system is open, overnight sure won't hurt! .....Jb

.
X2

I have put a vacuum on systems for a hour then let them sit and the guage hasnt moved. But later on it leaks down. I like using pressure on the system and then snoop or a small concentration of soapy water. If it has a big leak it will just blow the snoop off but you will probably be able to hear it.

Mike
69 Camaro Prostreet - purple w/ghost flames , 502 w/ 871 blower


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
prostreet69camaro is offline  
post #9 of 13 (permalink) Old Jul 11th, 11, 07:01 AM
Senior Tech
Dave
 
Join Date: May 2001
Location: Frisco, TX
Posts: 385
Re: My AC Gauge Reads -100 on Vacuum

If the system holds vacuum for several hours ABSOLUTELY stable, you are fine. Remember, you are filling the system back up with R12 which is a collection of VERY large molecules. Under vacuum,the smallest leak will allow atmospheric molecules to enter which are much smaller than the CFC's that make up R12. If the system stands up to the vacuum test, it will hold refrigerant pressure. The service manuals from GM do not mention anything about pressure testing a repaired system.

I am curious what type of vacuum pump you bought. Most automotive application pumps pull a system down to -30 lbs. All you need is to get the system below -26 lbs so any moisture suspended in the refrigerant oil boils out and is evacuated by the pump. 100 sounds very low, so if it holds that, you should be very confident the system is sound.

Also, I am surprised you bought a pump. Autozone rents them for free. I just borrowed one this past weekend to charge a friends Camaro. I see you live in the Dallas area like me, so now I know where I can borrow a pump if I need one again!

Dave

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

68RS/SS Convertible L48 (350/295 Powerglide)
daverichard is offline  
post #10 of 13 (permalink) Old Jul 11th, 11, 04:15 PM Thread Starter
Senior Tech
 
Join Date: Aug 2001
Location: Dallas, Texas
Posts: 847
Re: My AC Gauge Reads -100 on Vacuum

Quote:
Originally Posted by daverichard View Post
I am curious what type of vacuum pump you bought. Most automotive application pumps pull a system down to -30 lbs. All you need is to get the system below -26 lbs so any moisture suspended in the refrigerant oil boils out and is evacuated by the pump. 100 sounds very low, so if it holds that, you should be very confident the system is sound.

Also, I am surprised you bought a pump. Autozone rents them for free. I just borrowed one this past weekend to charge a friends Camaro. I see you live in the Dallas area like me, so now I know where I can borrow a pump if I need one again!
I messed up on the vacuum pump purchase. You sent me an email via Team Camaro just before you went on vacation. For some reason I over looked (or didn't remember) the part about AutoZone renting a vacuum pump.
I bought the $100.00 U.S. General vacuum pump from Harbor Freight. I am very suspicious of my gauges going down to -100 on the low side; because I had read my vacuum should go down to about -30 before I ever bought the pump.

Did you buy a can of "flush" before you charged your system? I bought a can last night on ebay. It should be here about the same time I get my cans of R12 from ebay.

I found a pretty good video on YouTube the other day that (for me) gives GREAT information concerning (almost exactly) what I'm doing to my car's ac system.


Oh, I bought the Pro6ten compressor like you suggested & you also talked me into sticking with R12. I had been on the fence concerning this issue for a while.
327!275hp!Convt! is offline  
post #11 of 13 (permalink) Old Jul 12th, 11, 11:54 AM
Senior Tech
Dave
 
Join Date: May 2001
Location: Frisco, TX
Posts: 385
Re: My AC Gauge Reads -100 on Vacuum

I did not flush my systems since I changed the hoses, condenser and evaporator with new parts and my compressor was still good. Flushing the evaporator is a very good idea if it has been sitting a while. Obviously do that with the compressor removed from the system.

I assume you have added mineral refrigerant oil to the compressor when you installed it. Definitely want to stick with mineral oil for R12. The instructions that come with the compressor may specify PAG oil, but that assumes you are using 134a.

I would look for a video on YouTube for charging the system. It is pretty straightforward, but knowing how to purge your lines when changing cans can help keep unwanted air out of the system and can make a big difference in the cooling ability when you are finished.

Dave

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

68RS/SS Convertible L48 (350/295 Powerglide)
daverichard is offline  
post #12 of 13 (permalink) Old Jul 12th, 11, 01:10 PM Thread Starter
Senior Tech
 
Join Date: Aug 2001
Location: Dallas, Texas
Posts: 847
Re: My AC Gauge Reads -100 on Vacuum

Quote:
Originally Posted by daverichard View Post
I assume you have added mineral refrigerant oil to the compressor when you installed it. Definitely want to stick with mineral oil for R12. The instructions that come with the compressor may specify PAG oil, but that assumes you are using 134a.
I called Old Air Products after reading your post & confirmed what you stated about using Mineral Oil. You know, there are really a lot of things those guys leave out in their little one sheet instruction page.
So now I am going to take the new compressor back off. I was planning on doing this anyway when I get the ac flush product in the mail.

How do I insure ALL the PAG 46 oil is out of the unit when I drain it? Just let it sit & drain until no more oil drips out?

Since my system takes 52oz of refrigerant, do I need to put in 8.84oz of Mineral Oil? The formual Oir Air Products gives is: 52oz. Refrigerant x 17% = 8.84oz. But they are referring to the PAG 46. Is it the same for Mineral oil? I forgot to ask Old Air about that when I called.

Thanks very much for the help & advice. It's hard to believe my little Camaro is actually so close to having a real live working air conditioning system.
327!275hp!Convt! is offline  
post #13 of 13 (permalink) Old Jul 13th, 11, 07:33 AM
Senior Tech
Dave
 
Join Date: May 2001
Location: Frisco, TX
Posts: 385
Re: My AC Gauge Reads -100 on Vacuum

You should use the same amount of oil if mineral or PAG. As for converting, drain the compressor through the ports for several minutes and turn the compressor several revolutions to make sure you get the majority out. PAG and Mineral oil are chemically compatible, so you do not need to get it totally out of the system and you should not flush the compressor in any way. The majority of the oil is in the compressor with some in the accumulator. I assume you changed the accumulator, so you should be fine. I would recommend flushing the hoses, condenser and evaporator before resealing the system.

Remember that you only flush free-flowing components, so you do not flush through the expansion valve, the accumulator, the compressor or the POA. I also recommend you flush in the opposite direction of refrigerant flow. This helps dislodge contaminants from the smaller passages. Use lots of shop air to get the flush out so it does not reduce the efficiency of the system or collect in the accumulator.

Dave

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

68RS/SS Convertible L48 (350/295 Powerglide)
daverichard is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome