It's not the cans pressure that can rupture anything it's the system pressure once you inject the freon and the compressor starts to cycle. The high side can run 300 to 500 psi.

Picture of low side port. Pretty much dead center in the photo it's under the black cap sticking up from the aluminum line.

 

I might be thinking of the V70 I will check today. We got 7 Volvo 850s N/A and turbos in for a/c work.

(in a racing announcer voice) Its that time of year again folks and here we gooo!

 

That's why I STICKYied the AC thread.

 

Quoted for importance. It is no small risk to mess with the A/C without a little knowledge of safety.

You are dealing with potentially high pressures and sub zero temperatures. Overfilling can certainly result in a line or connecting bursting, I've seen it happen. I'm not recommending against refilling it yourself, but be aware of what you're dealing with!

 

exactly why I have what is in red in my signature.

 

Physical danger is the main reason they changed fitting sizes when they went to R134. With the older systems (R12) the high side and low side fittings were the same and you could hook up a can to the high side and blow it up in your hand.
Now it's just a matter of the DIY'er coming back and saying it doesn't fit because they are trying to hook up to the only port they can find or the "easy" one and it's the high side and it's designed not to work on that one. If you are doing it yourself and you can't hook the line up to the connector you likely have the high side and you need to look a little harder for the other (low) connector.

Doing it yourself isn't that difficult but you need to read the directions, you need to have a gauge so you can tell how much is in there, you should watch a youtube video or three of someone doing it and take your time.
Without a gauge I'm not sure why you'd even try as you're just guessing and your chances of under filling or over filling are much higher than you getting it right. The result, you might end up on a really hot day with the windows down because it's cooler that way then with the system running.

With a gauge you'll do OK but you are still just getting into the ballpark but for most of us it will be good enough. You have to realize that temperature and humidity will dictate a different desired low pressure value in your system to indicate that it's full and that you are still shooting for an average and not an exact fill for your specific system and vehicle.

It doesn't happen very often but once in a while I've had people discharge their system because the pressure on the low side was too high !!
You only check the pressure while the system is running. If the compressor isn't turning the low side will equalize with the high side and the pressure in the whole system at any point will be the same. In most cases this will be well over 50 and even over 100 psi. It's normal, do not let any freon out of the low side unless you're positive the compressor is running. All the systems I'm aware of have both low and high pressure shut off switches to protect them. Unless you know what you're doing I don't recommend jumping the low pressure switch when you're doing a recharge. If you are really low on freon it does make it a little faster with the first can but you run the risk of something happening that you didn't expect and you can't get the jumper out of the switch fast enough and you fry the compressor. Just isn't worth it.

You pay the big money to a shop to evacuate the system removing all the freon. Then they pull a vacuum deep enough to actually boil any water that is in the system and remove that also. Then they should shut down the system and leave it in vacuum and see if it holds (leak check). This is the step a busy shop or lazy tech will skip thinking it doesn't matter or hoping yours isn't a fast leaker because they found some pressure in the system when they started. Once it's empty and dry they use weight to inject the amount of freon (and measured lost oil) the engineers designed the system to run on. Then theye should check the air temp at the ducts to insure customer satisfaction and that there isn't a blend door problem or something else hindering the AC system from performing as it should. This recharging procedure if done right isn't quick and it's why it's expensive. It takes a tech's time to do it properly and the machine isn't cheap.

 

If you are wondering about the different formulas of R134, the slightly more expensive ones do seem to give a better efficiency and cooler temp reading of the outlet air.

I've used the arctic cool and it does perform better that just straight R134. IMHO

 

Wow didnt think this thread was gonna get big any way i go to look a the pressure in the system with can of R134a with gauge on it, it read low so i had everything on let the car run for a bit be for adding when i started adding it the compressor did not engage and now im filled to the proper PSI so i start disconnecting the pressure switch the closest to the fire wall on passenger side to see if the clutch would engage but it didnt and i disconnected the other switch below the service port on the low side and that one kicked on the fan and now when i click the AC switch on and off the fan goes on and off too and at this point the compressor clutch does still not engage i try to add more freon and it wouldn't let me add anymore in stayed at 35psi. What did i do wrong here i have a feeling a messed something. What do you guys think about this situation??

 

If the ac switch is on, and the system has freon, and the car is running, and the fan is on full blast, I would probably bump the front of the compressor with a broom stick handle to see if that starts it.

 

you can't trust those dinky (yes they are dinky) gauges that attach on the small cans. Only manifold gauges will tell you the exact correct pressures.

there is a yellow sticker on the passenger side of the engine compartment that lists how much Freon in KG.

Pressure in the system may be correct but if the freon levels are still low you won't have cool air.

With the engine off take a test lead on the a/c clutch wire (round white connector by the compressor). run the lead to the positive side of the battery. Observe if the clutch is actually engaging. If it does -- still too little freon, or wiring issue (if you have correct presser and amount of freon). If it doesn't clutch is bad.

 

IF you're going to run it straight to the battery you best put a fuse in there just in case the AC clutch is shorted to ground. Otherwise that wire will burn off the insulation and anything else (your hand) it gets close to before it glows red and melts.

 

And yes the gauge you buy with a can of freon isn't deadly accurate but it's a trade off between buying a manifold set for a hundred bucks and then freon too or someone spending 25 to 50 on a big can of freon and a gauge that will get them in the ball park.

Can you trust it, you sure can for what the typical DIY guy is doing. Is it exactly 45.3 or 16.8 psi ?? maybe not but it's margin of error seems to have worked for any car I've helped someone use the store bought cans with a gauge on. That's seven years worth and yes I do own two manifold sets, R12 and R134a.
But that's the trade off with the DIY system. You may not get the maximum efficiency out of your AC system but that's why it's cheaper than having a shop do it. You may have it a little under or over filled but you've saved at least a 100 bucks and you need to choose on a really hot day when the system is struggling to keep you cool if it was worth it and or if you had the extra 100 bucks to spend in the first place.

 

I use the gauge to get close, and observe the temperature drop of the air coming out the vents to know when it's enough.

 

I use gauge set with a scale and a 30 pound cylinder. I have a dedicated vacuum pump hooked to my gauge set and a branch t. Its home brew, but it allows me to do a complete vac and charge in less than 30 minutes. that means $65 (which is our shop charge per hour for walk in work) and the customer will have correctly pressurized system and diagnostic (via the vacuum pumping before charge to check for leaks).

Im sorry, but its a ritual for me when I get a vac and charge job.

Pull car in, set up gauges, twist ****, turn on vac pump, wait 15 minutes (run Autologic diagnostic during wait) after 15 minutes over make sure holding negative pressure, close low side, run car a/c on full, re open low side, twist a **** other way, turn 2 other ***** open zero scale, double check sticker for KG weight, open 30 pound can valve until correct weight is emptied, close all *****, use infrared gun to check vent temps, out the door.

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@kiss frog

I for someone who may not have a $500 power probe that is another way of going about it.