How to recharge a previously working A/C

[francesconyc]

I want to attempt recharging my AC.
The PO told me the AC needs only to be charged, and it seems he was doing DIY as he came me some accessories I don't understand.

I just bought one of those blue, yellow, and red gauges.

now. all the youtube videos suck. they ignore to teach step by step.
is there anyone who can help me?

only thing I understood is that the blue line goes to the lower port, the red line goes to the upper port. that's it

[GH85Carrera]

The blue line goes to the suction side, and the red line goes to the high side, or pressure side. The yellow is the refrigerant connection.

The biggest "trick" is too understand the simple fact, you can't ever have too good of a vacuum. I believe in belts, suspenders and duct tape overkill method to charge the system. I pull a vacuum, for an hour, and let that sit overnight and see if it stays at the same reading. That tests the system at 1 atmosphere of pressure or 14.6 PSI at sea level. Not much of a pressure test, but is will show a bad leak.

After a overnight vacuum I charge with nitrogen to 100 PSI or so, and then brush on soapy water to any fitting I can access. Assuming no leaks, I pull a two hour vacuum. One more charge of nitrogen, and then I change the oil in the vacuum pump with fresh oil. I then pull a long pull and get to double digit reading in microns with a micron gauge. Then finally I know all the moisture is boiled out, and I can charge with refrigerant.

The purpose of a vacuum is to get all the air out of course, but the moisture in the air will boil out abut it can turn to ice, and "hide" in the system for a long time.

When you charge, and feel ready to remove the hoses, leave the engine running and carefully remove the suction side. Then tun off the engine, and wait for the pressure to equalize, then remove the high side.


This is my nitrogen rig. I bought it a welding supply place. The regulator gets the pressure to what you want, and they welding supply place had it. I just asked for a AC service nitrogen regulator. They "sell" the nitrogen tank, but it is really something I just take back, and the swap it for a full bottle for $25 bucks or so. The nitrogen rig is handy to fill tires as well.

The micron gauge is just something needed to see the pressure change at the bottom of the gauge range. 50 microns is 0.0009668388935658 PSI 200 microns is 0.0038673555742632. Neither of those will show up on an analog PSI gauge. You want to get below 100 microns if possible.


Hopefully you have barrier hoses now. There are about 27 feet of hoses, and multiple components for the moisture to hide in.

If you system has been open to the atmosphere, replace the receiver dryer before recharging.

[David Inc.]

Spoiler alert, the PO was lying and there's definitely something wrong with the system. If what Glen is talking about doesn't immediately make sense you're better off having the system checked out by a professional.

It's not a terribly complicated system but it's definitely possible to make it worse if you don't know what you're doing.

Edit: Oddly enough one of the best and most straightforward descriptions and how-to's for auto A/C I've ever seen is on the something awful forums.

https://forums.somethingawful.com/showthread.php?threadid=3970674

[911convert]

I found the Youtube videos to be quite good. ChrisFix does a pretty good job describing, even though the test vehicle is a Tacoma. Its pretty much the same.

https://www.youtube.com/watch?v=Pdq8JAlct6s

Never fill on the high side. In fact, do yourself a favor and close the red valve on the high side by turning the knob clockwise. Never open it. You'll damage something else but more importantly hurt yourself.

Now, if your hoses are original, you need to replace them with barrier hoses first. The refrigerant will just leak out out through the hose and not through the joints.

[GH85Carrera]

Originally Posted by 911convert

I found the Youtube videos to be quite good. ChrisFix does a pretty good job describing, even though the test vehicle is a Tacoma. Its pretty much the same.

https://www.youtube.com/watch?v=Pdq8JAlct6s

Never fill on the high side. In fact, do yourself a favor and close the red valve on the high side by turning the knob clockwise. Never open it. You'll damage something else but more importantly hurt yourself.

Now, if your hoses are original, you need to replace them with barrier hoses first. The refrigerant will just leak out out through the hose and not through the joints.

The high side should be connected to to the system just to read the pressures. If the high side is getting up to 250 or 300 and the low side is now in the 40s and cold air coming from the AC vents, you have an issue with a blockage. Get a good pressure chart to see the ranges you should achieve.

But yea, be very sure the red valve is closed when adding the refrigerant.

And if you do't feel comfortable doing it, hire a pro, but do a long vacuum pull before he touches it. You can't afford a pro to spend hours pulling a hard vacuum. Most AC pros work on systems with all the components right in the engine compartment. They are not familiar with the long hoses and all the condensers in the front and back.
Spend a LOT of time getting a good vacuum.