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Can gauges introduce air?

2000_civic on Mon June 23, 2008 8:08 PM User is offline

I was just wondering what happens to the air in the hoses attached to a gauge set. Does it end up in the system? If it does is there a method to purge it? Forgive me if this is in the FAQ section, but I took a cruise through there and didn't see it.

bigkev on Mon June 23, 2008 8:18 PM User is offline

yes the can. In the read only part of the forum the say something about purging some by cracking a hose. On my gauges (mastercool) I have an extra center port with a schrader valve type fitting that i can hook my pump up to to get all lines and gauges pulled in a vacuum. I read something in a haynes manual that seemed interesting the other day. They said you hook you vac pump to your high side gauge, blue to low side on vehicle, and yellow to refrigerant. After you pull the vacuum they say you close the high side valve and unhook the pump. After you get the system charged by recommended capacity you can then hook up your high side gauge and not introduce air, or so they say. I personally like doing it my way by vacuuming on the extra middle port on my gauge.

bigkev on Mon June 23, 2008 8:26 PM User is offline

I quit being lazy and went and found the thread:

Also, a trick I did the other day was neat while playing around with my Ac. Normally when I have wanted to add a little oil or leak detector i have taken out the schrader valve and tried to pour the oil in. They make an inline tool that does this also. The other day I had an idea. I hooked my pump up to my yellow hose, Hooked my blue up to the low side, and hooked red up to the high side. I closed the high side valve so vacuum was only being pulled on the low side. I unhooked the red hose from the gauge, not from the vehicle. Now I can use the red hose to pull in any oil or leak detector that I want.

GM Tech on Mon June 23, 2008 10:32 PM User is offline

I've been doing that for years- but I use the blue side to pull the oil into the low side-where the compressor can get it first-- pull the vacuum on the high side- then re-attach all lines- but now since I have a machine I can also use it to introduce my pre-mixed with dye oil......

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Mon June 23, 2008 at 10:33 PM by GM Tech

2000_civic on Mon June 23, 2008 11:35 PM User is offline

So if I pull a vacuum in my gauges before I attach them I can prevent air from entering my system. Will I have to add a small amount of 134 to offset the refrigerant that gets pulled into the gauges? And The method for adding dye and oil ya'll mentioned is interesting! I don't quite understand it yet though. Is this what you're saying?

1) Pull vacuum in gauges with the low side valve open and high side valve closed

2) Add oil or dye to high side hose and attach it to the gauge set

3) ?

I don't quite get the next step. What do you do with the air in the high side hose after that?

2000_civic on Mon June 23, 2008 11:40 PM User is offline

O.K. It looks like I botched step 2. So the high side hose was on the gauges with the valve closed and then removed from the gauge while connected to the car? Is this done on a charged system?

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