Automotive Air Conditioning Information Forum

Hi all i'm attempting to put in a ac system on a 1986 Toyota corolla gts. When running a vacuum and checking to see if the car will hold a vacuum do you open both high and low sides while running vacuum and then close both sides to check if it will hold a vacuum?

The first time i only had the low side port connected....i didn't even hook up the high side hose. I drew a vacuum for about 10 mins and the gauge read 27 then after 3 hours it read 24.

Then after watching some youtube vids I currently have vacuumed for 20 mins on both high and low side and have both high and low side holding vacuum. Now the low side is at 29 and The high side gauge didn't have a vacuum gauge side but the needle did get sucked back to below zero and is pinned to the, for lack of better term, pin. Will update after results tomorrow morning.

Thanks for your time.

Yes, should open both low and high side service gauge valves while pulling your vacuum.

And - of course - any loss of vacuum means one should check all gauge connections for leaks too.

When you add refrigerant initially after the vacuum has held, you can add as a liquid though both sides as the engine will be off. Then you close the high side valve, then you start up the engine and AC to add the remainder.

I know you already know to purge the air out of your lines with a little refrigerant.

Cusser wrote:Yes, should open both low and high side service gauge valves while pulling your vacuum.

And - of course - any loss of vacuum means one should check all gauge connections for leaks too.

When you add refrigerant initially after the vacuum has held, you can add as a liquid though both sides as the engine will be off. Then you close the high side valve, then you start up the engine and AC to add the remainder.

I know you already know to purge the air out of your lines with a little refrigerant.

Thanks Cusser,

Ok I let the vacuum hold until morning.....a good 9 hours....and the gauge shows still 29 vacuum on the low side....didn't move a bit. However on the high side gauge last night the needle was up against the pin but this morning it had moved slightly off the pin......does this mean I have a leak somewhere? Even though the low side stayed perfect? Thanks.

You should be fine.

Cusser wrote:You should be fine.

Thanks again!

Cusser wrote:..................................

I know you already know to purge the air out of your lines with a little refrigerant.

Hi,
I'm a newbee here & appreciate if you could explain on, how to do this.
I thought once you start vacuuming everything is drawn out except PAG oil already in the system.

thanks in advance

Remember vacuuming the system is not the same as evacuating the r134 in a system....if you had a leak or replaced a component of the system then you had to evacuate the refrigerant in your system....the reason for vacuuming the system is after you have repaired the system and it is sealed....you put a vacuum on the system in order to take out any moisture in the system that got in there while the system was opened to the atmosphere. Then if your system can hold a vacuum without leaking.....then you know it will be ready to charge with the refrigerant.

The purge is a schrader valve on the ac service manifold that when after you connect your refeigerant to the manifold service line you press the schrader valve until refrigerant comes out of the valve....this ensures you will not put air back into your ac system. Then you follow your fill procedures after your purge. Here is a helpful video that explains the steps pretty well.
https://youtu.be/Pdq8JAlct6s

I said "system" a lot didnt I?

Good luck.

That you tube video has some bad info. Most gauge sets do not have a schrader at the yellow hose for purging. You would crack it loose to purge the hose. Also, put the blower on high speed not low speed. The you tuber was adding refrigerant as a liquid. you can not do this unless you are charging a system with an accumulator or you are experienced in charging systems. If liquid hits your new compressor, you can damager its valves. It is also a bad idea to weigh the refrigerant on a scale with the hose hanging down. You need to support the hose so it won't influence your weight. You can not add oil into the yellow hose. It will not work well. Oil should be introduced either while the system hoses are open or use an oil injector.

Thanks Guys.
As Dougflas mentioned, my gauge set has no schrader valve and I just crack it loose a bit and release some gas out.

Dougflas wrote: ↑Thu Feb 16, 2017 2:45 pm That you tube video has some bad info. Most gauge sets do not have a schrader at the yellow hose for purging. You would crack it loose to purge the hose. Also, put the blower on high speed not low speed. The you tuber was adding refrigerant as a liquid. you can not do this unless you are charging a system with an accumulator or you are experienced in charging systems. If liquid hits your new compressor, you can damager its valves. It is also a bad idea to weigh the refrigerant on a scale with the hose hanging down. You need to support the hose so it won't influence your weight. You can not add oil into the yellow hose. It will not work well. Oil should be introduced either while the system hoses are open or use an oil injector.

Hi Douglas,

Here's one for you. Prepping to charge a new Vintage Air system on a hot rod. I attached gauges to both high and low side. Pulled a vacuum for an hour. Question is, only the high side gauge would drawn down to 30hg. The low side gauge didn't move at all when applying vacuum. Is that a problem? Should both gauges give a reading or just one? Overnight, high side gauge remained at 30hg. Appreciate your help.