R134 refrigerant in a can

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Anyone use those cans of r134 to refresh a/c systems? They're fairly idiot proof. They come with an attached gauge, they only fit the low side port, etc. My question is, is the gauge a "smart gauge" meaning if it indicates a properly charged system will it prevent you from adding refrigerant to the point where you might risk overcharging the system. Both of my cars started off in the middle of the green so to speak but after several seconds of hitting the trigger even though the gauge didn't budge the a/c is noticeably cooler. Does a little go a long way?
 
The only proper way to charge is vacuum the system, measure the refrigerant correct the level and recharge.

Rod
 
It is said that the last couple of oz of refrigerant does all the cooling. The rest of the charge is there to push those few ounces where they need to be.

As noted, the gauge doesn't really mean anything. If a couple of hits from the can don't make it cold, STOP and seek professional help.

A modern car typically has less than 20 oz of refrigerant in total-- so a whole can is a huge amount for it. If all or nearly all of your refrigerant has leaked out it will just leak out again pretty quickly.
 
Last edited:
Originally Posted by ragtoplvr
The only proper way to charge is vacuum the system, measure the refrigerant correct the level and recharge.

Rod

x2. The low side gauge is a gimmick to get you to buy the thing. We need a high side reading to get the charge even close.
 
Thanks to all. Actually I'm just [censored] around looking for things to do. Cars in question are a 2012 Versa and a 2013 Sentra. Neither system touched since new and to be honest they both blow pretty cold. I will say they're a tad colder since I tinkered with them but I think I'll stop here.
 
Yeah I wouldn't futz with something that isn't broken unless you have the tools to make sure you're doing it correctly (i.e. not overcharging.) The recharge kits with the cheap low pressure gauge are good a quick top-up to get a leaking system cold again, but it's not much help measuring the correct charge or determining whether the A/C is working correctly.

A manifold gauge set is $50 at Harbor Freight and will tell you a lot more. It's not rocket science, lots of how-to's online which help decipher what the numbers mean. Basically at a given temperature a good working system with proper fill will have a normal range of high / low pressure readings, that's what you shoot for when you're topping up on charge. That will get you in the neighborhood of the correct charge, but the best way is to vacuum and refill with the correct amount of refrigerant instead of just shooting for "close enough."
 
If you're going to do what you're doing at least get a vent temp so you can tell for sure if you've made an improvement. Low 40s should be your target. High 30s, run away, you've got perfection.

Holding the can while it discharges cools your hands off so they aren't a good feeler for an A-B comparison.

Remember every time you hook up the hose you add a squirt of normal air-- and it's inherent humidity.
 
Ya. Thanks all for advice. I was very cautious with what I did. It amazes me how some a/c systems are trouble prone and some like mine are seemingly tight and leak free after 7-8 years on the road. Design? Dumb luck?
 
Originally Posted by Aredeeem
..... and to be honest they both blow pretty cold. .
I will say they're a tad colder since I tinkered with them but I think I'll stop here.


Yes..... STOP while you are ahead!!
 
Thanks Linc. I will. I will. My wife just told me there's a sparrow building a nest in my dryer vent. Thank God, I thought, something to do to tomorrow.
 
If you overcharged R134. it will gets warmer.

Unless you want the AC to go warmer, then stop trying to make this a project. LOL!!!
 
Line set, R134 without anything else in the can except possibly tracer dye. No oil or conditioners to contaminate your system. I was watching that South main Auto guy on youtube and he is claiming a natural loss of refrigerant every year.
 
Unless that car's last stop is a junkyard, stay away from that AC Pro stuff. The only things that belong in the refrigerant loop of an HVAC system is refrigerant and oil - UV dye if need be as well. AC Pro and the like have sealers, seal swell agent(usually MeCl), methanol and dye. That will do a number on a recovery/recharge machine and contaminate recycled refrigerant.
 
You can get a set of gauges from Harbor Freight and virgin R-134a. The key to using them is to learn how the service valve couplings work and the high/low pressures of your system - and purging air from the hoses.
 
I just had our 06 Odyssey in the shop for its first AC recharge since it was blowing cold only on the pax side. They said out was a can low, charged $65 incl $45 in labor. I could see a lot of stain in the engine compartment by the fill valve. Blows cold now.

I used the AC pro sparingly on my 03 Accord with good results. Wouldn't put it on the odyssey but if you don't care about the sealers , it's not a bad alternative.

Others have recently complained about the quality of HF gauges, but I haven't used them myself.
 
5 bucks a can at Walmart, it is good stuff.

No need for the expensive ones with all the oils and such, if it is a Low Refrigerant problem, they will do the job. Blessing for all us with just the low side hose that know what the problem is, I believe the first reply was about why they shouldn't be used but in reality they work fine.

One thing of note I would like AC expert to chime in on is also someone repeated the claim that some refrigerant is lost just by using it over time. I have heard this too. Ol' SK says that some has to, a very small amount, or the AC wouldn't work properly. Others also hint that a small amount leaks out over time, over normal operation and nothing else, thus the primary (only?) reason the $5 can (~$20 at Autozone, usually for same size and stuff) apparatus is sold at Walmart and other places. Buy a big can for the hose, then don't use the big can and buy small cans if needed. Same price, really.

Do systems really lose some charge over time, or is that just old wives tale?
If so, how much lost is normal?
If so, how much time until it feels less cold?
 
Yes, some always leaks out. It is not a hermetically sealed system like a refrigerator.

Barrier hoses are much better today than they were 25 years ago, the amount of leakage is far smaller today than it was back then.

It will feel less cold when enough has leaked out that gas is presented at the expansion valve instead of liquid.
 
If you over-charge an AC system there is a real danger of liquid refrigerant getting sucked into the intake of the compressor. Liquid refrigerant is not compressible and the compressor can very easily be seriously damaged if liquid refrigerant is sucked into the intake. Once that is done the compressor has to be replaced if you ever want the system to work again, that is a very expensive repair.
 
My 04 Camry AC system uses less than twenty ounces of r134. Difference between not enough and too much refrigerant is less than three ounces. Our local Toyota dealer will NOT add refrigerant to an AC system.
 
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