Topping off R134a - how to?

[WestPoint]

Happy Thursday everyone, I used the search function but did not find anything conclusive.

I realized I am a bit low on the refer charge and thus I want to add more R134a in. Probably need to use hot water and take my time to get in more refrigerant as vapor via low side. Since the system is now closed, what is the best way to go about hooking back up the couplers and purging the lines?

If my thought process is correct, please let me know:

1.) engine is off and manifold controls CLOSED
2.) hook up quick couplers to low and high ports which will give you pressure readings
3.) turn on engine
4.) hook up central/service line to R134a bottle and purge at manifold connection
5.) purge low-side and hi-side lines by unscrewing momentarily at manifold to allow R134a to fizz out
6.) now add R134a to desired spec ONLY to low side. Close low-side manifold valve.
7.) remove the low side when its running then remove the high side with the engine off, it gives the lowest pressures in the lines.

[tbirdtbird]

How do you know it is low on refrigerant?
How will you know when you have enough?

I thought you charged this by weight from previous posts?
That is the only correct way, not by pressures

BTW many of us bleed the liquid refrigerant that is in the hi side hose back into the low side so as to not lose any refrigerant

[WestPoint]

My car takes 18.7 oz MAX. I did attempt to charge by weight but I realized my setup was terrible by the time I was filling via suction side.

I charged probably 11.5 ounce from first can (.5 approximation from bleed off). Fill net wt is 12oz

The next can I weighed again after disconnecting since it's hanging off a stiff vacuum hose. I got roughly 9.7 ounce on the scale. So a rough estimate is 2 ounce from second can got in? There's still refrigerant in the manifold and service line which I didn't bleed off yet.

Assuming I only got in 13.5 ounces, I am a few ounces off from the min spec which is around 16 or so ounces.

[JohnHere]

The previous questions and comments by tbirdtbird are right-on.

As for me, I don't use the small 12-ounce cans for charging. It's just too difficult to "juggle" them and to get the correct charge in, as you discovered. It's much easier to place a 30-pound tank on the scale and let the scale count up to the desired weight-of-charge and then, turning off the refrigerant flow. Some scales even do this for you automatically.

I also purge the high-side hose into the low side before disconnecting everything, as tbirdtbird mentioned. Again, it's much easier doing that instead of trying to evacuate and pre-charge each hose.

[WestPoint]

Hindsight is 20/20 and next time around I won't be using these little cans. It wasn't wise at all to use a 1/2" Appion vacuum hose to charge dinky little 12 oz cans I deserve the genius award for that one.

[tbirdtbird]

Suggest let pro recover, evacuate and charge by weight.
You used the word 'assume' too many times and you never get all 12 oz from the cans, they really are a downer

[tbirdtbird]

Tim carries an electronic scale, see this link
https://www.ackits.com/accu-charge-elec ... gerant%20s

This type of scale is what the pros use and eliminates guesswork, gets you an accurate charge, and the best performance. A whole different world. Those little cans are to me a bit of a joke