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Old 03-19-2021, 09:48 AM   #1
bandit0067
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How do I find a leak in the AC system...

Guys, I got a one owner 71 GMC 1500 with factory air. The original compressor was not locked up but the clutch hub would not engage. I rebuilt the original engine awhile back and just now trying to get the ac going. I put in a remanufactured compressor and found I have a leak. The factory installed system has not been opened and I ran the new compressor a short bit I can find no evidence of leaks in any outside joints of oil. Looked for leaks with a soap solution on the pressurized system showed nothing. Been a while since I did some trouble shooting on one of these and was wondering if any new technology is out. I see cans of drop in with leak stop and leak check but not sure they would be ok in my original 50 year old system. Any ideas or opinions on how to proceed.....thanks.....
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Old 03-19-2021, 11:39 AM   #2
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Re: How do I find a leak in the AC system...

Get you a bottle of A/C oil florescent dye and a ultraviolet light you will find the leak. These are examples only you will need to determine what weight oil your compressor requires. Once repaired any future leaks are found real easy with the light.
I put this in all of my systems even when it's a brand new install.

https://www.amazon.com/Blacklight-Fl...xpY2s9dHJ1ZQ==

https://www.amazon.com/TSI-Supercool...s%2C244&sr=8-6
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Old 03-19-2021, 11:44 AM   #3
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Re: How do I find a leak in the AC system...

One of these is a must have in my book also

https://www.amazon.com/Podoy-Injecto...s%2C244&sr=8-9
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Old 03-19-2021, 12:30 PM   #4
bandit0067
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Re: How do I find a leak in the AC system...

Thanks Sheep, as I understand things, the original system used mineral oil and that oil is still displaced thru out the components . The replacement compressor contained 3 oz of oil, but did not say which . I am pretty sure it was PAG oil of some weight. I use a drop in R 12 replacement gas and it works great in several of my older cars. They say this gas will pickup and move both the new and old oils the same. Do you have any idea how much of this leak detecter oil I could add and NOT overfill the system. thanks....
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Old 03-19-2021, 12:43 PM   #5
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Re: How do I find a leak in the AC system...

Hope you have more than 3oz in that system. They take a lot more than that to keep that huge compressor from locking up. The additional dye will not really affect the overall. All you really need is about a tablespoon of the dye. When I get a fresh bottle of oil I just put the dye in that. That way any system i put together automatically gets dye in it
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Old 03-19-2021, 01:38 PM   #6
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Re: How do I find a leak in the AC system...

As an HVAC tech I always start with the good old fashioned method of using Big Blue or Cal-Blue leak detector. You spray or brush it onto the fitting and lines and watch for bubbles. You should be able to pick some up for around $10 at your local home improvement store, supply house and maybe auto parts store. The key with the spray bottle is to pull the trigger slowly so you don't create a bunch of bubbles. Brushing it on works even better. I have found some very slow leaks using this technique, this stuff blows some big bubbles. Dish soap will work on larger leaks but wont bubble up like the Big Blue. If I cannot find the leak with the bubble method i go to my electronic leak detector. If I cannot pinpoint it with the electronic detector then i use dye & UV light. Since most guys don't have the specialty tools I suggest starting with the bubble method. Good Luck!
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Old 03-19-2021, 01:53 PM   #7
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Re: How do I find a leak in the AC system...

Quote:
Originally Posted by kwmech View Post
Hope you have more than 3oz in that system. They take a lot more than that to keep that huge compressor from locking up. The additional dye will not really affect the overall. All you really need is about a tablespoon of the dye. When I get a fresh bottle of oil I just put the dye in that. That way any system i put together automatically gets dye in it
^^^^^^^^^^^^^^^Good method also^^^^^^^^^^^^^^^^
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Old 03-19-2021, 01:57 PM   #8
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Re: How do I find a leak in the AC system...

Quote:
Originally Posted by bandit0067 View Post
Thanks Sheep, as I understand things, the original system used mineral oil and that oil is still displaced thru out the components . The replacement compressor contained 3 oz of oil, but did not say which . I am pretty sure it was PAG oil of some weight. I use a drop in R 12 replacement gas and it works great in several of my older cars. They say this gas will pickup and move both the new and old oils the same. Do you have any idea how much of this leak detecter oil I could add and NOT overfill the system. thanks....
A teaspoon or 2 will do it for the dye but you will need to determine how much oil your system/compressor requires.
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Old 03-19-2021, 09:38 PM   #9
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Re: How do I find a leak in the AC system...

Stock systems of old ran about 9 to 10 oz as my finding show. Breaks down to 3-4 oz in the compressor, 3 oz in the condenser , 1-2 oz in the filter dryer and some small amount in the evaporator coil. Of course all this does change as the system runs and more so if a leak is big enough. I just used soap bubbles and have not heard of Big Blue solution. Hoping the leak is not in the evaporation coil but maybe so and it prolly needs cleaning anyway. Prolly a rat nest or something as this ole girl has been an outside work truck all this time. Thanks guys.....
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Old 03-19-2021, 10:09 PM   #10
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Re: How do I find a leak in the AC system...

I've lived in the hot part of Texas all my life.. Automobile AC systems really get a work out down here.. When I worked as a mechanic, half of the cars that came in during the summer were needing AC repairs, and about half of those were leaking evaporators..

All the dye and brush-on bubbly stuff in the world won't detect a leak in the evaporator unless you have X-ray vision and can see through the case. You'll just stumble around in the dark. If you want to do professional type AC work on automobiles, get yourself an electronic leak detector.. The good ones are pricey..
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Old 05-07-2021, 02:51 PM   #11
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Re: How do I find a leak in the AC system...

Hey Guys, I found my leak and got the system gassed and it is cooling better than I expected. So now I need to know where the flappers are supposed to be. As y'all know they are vacuum activated and my tubings are rotted/gone. Im talking about the flapper on top of the cowl and flapper on passenger side vent. My cowl flapper seems to fail open. Under normal AC mode is it supposed to be open or closed.....and also the side vent. Seems I shall have to move and set them manually for now. thanks....

PS. In running the AC , the fan started blowing the remnants of a rats nest out of the vents. So, with the cowl flapper being open always, Im sure there is/was a nest in there. How would be the easiest to get to the coil to clean it out. Can you take off one side of the ac coil in the engine compartment , the side towards the engine looks the easiest. ......
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Old 05-07-2021, 03:20 PM   #12
leddzepp
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Re: How do I find a leak in the AC system...

With the AC on the cowl flapper (fresh air) should be closed and the passenger kick panel flapper (recirculating) should be open.
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Old 05-07-2021, 10:14 PM   #13
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Re: How do I find a leak in the AC system...

Got it. Just what I needed, many thanks....
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Old 05-08-2021, 01:00 AM   #14
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Re: How do I find a leak in the AC system...

For all the work you're doing on that AC system, you need a service manual. If you don't have one, they're available all over the internet.. Google is your friend.. I don't have a GMC service manual within reach but I do have '71 C/10 manual.. For what you're doing, a Chevrolet manual will suffice.. In section 1-A page 31, 32, and 33 are the cable and vacuum line diagrams.. Shows where each vacuum hose connects to those "flappers", as you call them...
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Old 05-08-2021, 11:24 AM   #15
bandit0067
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Re: How do I find a leak in the AC system...

You are right about a manual Rusty, I have gotten by with an old Motors manual long enough ......
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Old 05-08-2021, 01:14 PM   #16
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Re: How do I find a leak in the AC system...

Here is a few threads about the flappers and doors.

Thread started in 2008: https://67-72chevytrucks.com/vboard/...+control+panel

Thread started in 2016:https://67-72chevytrucks.com/vboard/...+control+panel

Theard started in 2005:https://67-72chevytrucks.com/vboard/...+control+panel














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