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When do we call it "done"?

TominKY on Sat July 19, 2008 10:09 PM User is offline

Year: 1997
Make: GMC
Model: Suburban
Engine Size: 5.7
Refrigerant Type: 134a
Ambient Temp: 82* F
Pressure Low: 35
Pressure High: 185


I posted earlier asking questions about an educated guess (yes, I know they are dangerous ) for the proper amount of oil to add to my accumulator. I settled on 3 oz. To make a longer story shorter, I got everything installed, vacuumed it down for an hour or so, and added the refrigerant. I do not have access to a 30 lb container, so I had to opt for the 12 oz cans. My system calls for 68 oz of 134a. I went through 6 12 oz cans, which adds up to 72 oz, but I think purging the lines between cans will bring me back pretty close to 68 oz.

I ended up with the following:

Test#1 - 8:35 PM - truck running at idle, front air set to MAX, rear air off, front windows rolled down
Ambient temp: 82*
Evap Inlet Temp: 65*
Ctr Vent Temp: 49*
High Side: 185
Low Side: 35

Pressures with front + rear air on max:
High Side: 200
Low Side: 50

I took the truck for a run up on the interstate and around some side roads. Vent temp seemed to stay around 42*, although it dropped to around 38* at one point for a short time. I threw the gauges on it after I got back, and got the following:

Ambient temp: 80*
Ctr Vent Temp: 42*
High Side: 155
Low Side: 32

What temperatures should I expect from this system when it is functioning correctly? I feel like there is another 5-8* in temperature drop in there somewhere, and my pressures make me think I might not be quite fully charged - especially the second set of readings. I am going to check it again in the morning - if the pressures seem lower, I guess it is time to start looking for a leak somewhere, although it held vacuum for well over an hour. I know it is best to have the proper scales and charging equipment with a 30 lb container, but that is just not in the cards right now. I think I am close, but as it stands now I don't think the air will be able to keep up on a very hot, sunny day.

I would appreciate anyone's advice and opinions. Should I add a few more ounces, or hold off? I don't want to overcharge it, because that will also cause problems.

Thanks for the help! This is an awesome board!


Chick on Sat July 19, 2008 10:24 PM User is offlineView users profile

When you first started, the pressures look perfect.. After you were all done, the high side seems a bit low..Could be one of two things..,Either you have a slight leak, you'll know tomorrow, or you're "DONE" ...looks fine to me as far as vent temps for a dual system... hope this helps...

Email: Chick


Freedoms just another word for nothing left to lose

TominKY on Sun July 20, 2008 7:57 AM User is offline

Hi Chick, thanks for the reply - Man, you are all over this board!

I agree that the second reading seemed a little low, but I am confused that I got a drop in the vent temp with this reading. I guess it could be that the interior of the vehicle had a chance to cool down more. I will do a visual inspection for leaks later this morning, and throw the hoses ack on it.

TominKY on Sun July 20, 2008 7:29 PM User is offline

Well, so much for being "done"!!

I was getting ready to reinstall the straps that hold the rear refrigerant lines in place, and I noticed that once again I have a pinhole leak in my high pressure line. This is an inch or so from where the original repair was made. Apparently it is another porous spot from corrosion caused by the "protective" rubber hose that GM put over the aluminum line. My big decision now - whether to take another shot at TIG welding the defect, or just bite the bullet and spring for the new, $175 line from the dealership. I suppose it might also be possible to splice a new piece of line in place of the corroded section, but I would have to get all of the bends just right. It might also be possible to braze in a coupling and go with flexible line up under the hood, but it comes pretty close to the exhaust under there. I am bummed! The place where it is leaking is not even that corroded,, but I can see it bubbling out slowly.

I guess I also need to see if a local shop will recover the charge for a reasonable fee, if I want to be enviro-friendly. I wish I had an empty 30 lb cannister laying around - I figure I might be able to vacuum the tank real good and store some of the leftover charge. I did this with R12 in the past. Has anyone else had any success with this?

Chick on Sun July 20, 2008 10:02 PM User is offlineView users profile

Do a search on the board for dual system Burbs, I know this has been brought up a few times..possibly by Gm Tech, and I just can't remember the easiest fix for those lines, but yes, it's a common leak spot..Maybe one of the guys will see this and respond..good luck with it..

Email: Chick


Freedoms just another word for nothing left to lose

TominKY on Sun July 20, 2008 11:33 PM User is offline

Hi Chick,

I tried searching with several different terms, but did not turn up anything discussing leaky rear air lines. I might try posting a new topic to see if it catches anyone's eye who has dealt with it before.


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