Is there a definitive answer on whether it is okay to recharge the AC using pure 134a?

The "gauge" on a refill can is nothing but a pressure gauge.

You might think a pressure gauge tells you something about how much refrigerant is in the system, but it's really not that simple.

Refrigerant gases are chosen for having a phase change to liquid that's right in the useful range of temperatures and pressures. So your gauge will only show "low" when the charge is so low that there's no liquid left.

Any time the system is off and in equilibrium and any amount of the charge is liquid, the pressure gauge is just going to show you the same pressure you could look up in the saturation pressure chart for that gas at that temperature. So it's really just a thermometer with funny markings.

Finding out if the amount of charge is correct is a whole more complicated business.

I don't think you're going to get "solid confirmation" that what you propose is all you need to do. You might read the reasons it might not be a good idea, but decide for your own purposes you'll try it anyway. It's possible you'll get the system to operate and nothing bad will happen, or at least not for as long as you care about. You pays your money and you takes your chances.

 

I've shot my wife's car with 134a in my 2013 and my '09 i'm running AC 12a which is a hydrocarbon blend gas it's a little bit colder than r12 people here don't want to hear that but it's been this way for years and I see no reason to change it for fear of i'm not sure what I do have an air conditioning issue on one of my pre and it is something electrical coating it has nothing to do with gas and charging but I am 134a and ac12a charged up and running in a six cars for about the last 12 or 13 years and if memory serves me correctly i've not had to add any gas or anything that whole time and my air conditioning is ice cold in all vehicles

 

Hello, I am considering "topping off my ac" are you still in favor of doing that?

 

Your AC came with 134a in it from the factory now it's low maybe You see a lot of bubbles in the sight glass maybe? So what else would you fill it up with? Probably 134 a don't you think?

 

Are you making cold air now what is the little gauge say when you stick it on to the fat line like you're going to put gas into the vehicle air conditioner running what's that gauge say 20 lb instead of 35?

 

Yup like Tom said look in the sight glass if it looks like a snowstorm going past the lens real fast you have a leak. Most likely in the expensive evap coil under the dash. I took good care of my evap lots of coil cleaners up the drip tube doesn't matter it lasts about 12 years. Which I thought was a good run. Some cars last longer. But my AC guy had one in stock its so common. i was smart enough not to run it with low refrigerant which damages the compressor. So my compressor was ok. If you smoke the compressor then its another probably $1200 today money.
So you can see if you lunch the compressor and the evap coil is leaking the car is close to totaled in today's climate.

But you have a leak. How bad who knows. I bet now its around $1400 to have the evap replaced. I do know driving a G2 with no ac is the absolute worst. I couldn't do it. And can't drive with the windows open the buffeting is insane.

Its an old car. It was a great car stellar reliability now its a very old car.

 

The sight glass is unreliable in a variable capacity ac system. Generally the right way is to remove the remaining 134a, pull a vacuum and weigh in the new refrigerant. One 10 oz can is not enough, two cans are too much.

Requires a recovery machine and cylinder, a gauge set, a vacuum pump, and an accurate refrigerant scale.

Optionally you weigh the recovered refrigerant to know how much was lost since the last fill. Plus a micron gauge for the vacuum.

Use the sticker under the hood for the amount.

Example Prius v:

 

Well I must be the rare bird of the whole flock for sure because in all of my Toyotas all the way back to hang on air conditioners made by Nippon denzo in the early '70s in my Toyota Corolla 1.2 l KE series cars I have never had an air conditioning failure yet especially the inside evaporator coil the one that's in the dash hanging below the dash wherever it is I've had a few condensers fail in front of the radiator usually because of wrecks or something hitting that condenser I've had a few compressors go bad and I mean a very few most of them lasted well over 200,000 mi even in the '80s even the upright Tecumseh style look like a little engine hanging off the side of your real engine for your car was quite the thing turn it on in the whole engine of the car would almost die It took so much juice to make the cold. But ripping dashes apart like general motors people are accustomed to and trucks and whatnot I have never even thought about never had to All of my leaks and funny business have been under the hood I've had hoses bust apart the metal and rubber combination things that go from the compressor to the firewall that sort of thing. Usually almost every used old Toyota I've ever bought or owned All I did was hook up a yellow charging hose straight from a can invert the can and watch the sight glass and try not to overfill I always want to see a bubble go by every so often if it's completely clear forever I'm slightly overcharged at least that's what I believe and always heeded that . And I've had ice cold snowflake blowing air conditioning since I was a teenager always in every old piece of car I've ever had air conditioning was just important as the car going forward and the turn signals working in my life.

 

Agree. Never had a Toyota I owned leak refrigerant. Which includes three hybrid variable capacity ac systems over a 15 year period.

They sometimes get dirty sock syndrome (musty evaporators) but the Toyota evap cleaner works quickly for at least four or five years at a time. I added some length to the condensate drain to make it accessible from the wheel well for easy injection of the cleaner.

Domestics and Hondas I have owned have leaked but were easy to get close without special equipment. However pulling a vacuum and weighing in provided optimum cooling on those as well.

I have seen evaporators and heater cores replaced in hybrids. It is not a pretty sight.

 

Unfortunately personal experience isn't very accurate statistically, unless I suppose you are a mechanic and fix hundreds of these each year. The evaporator on our 2007 leaked and the dealer's repair department (it was under a "we give you a good warranty when you buy this used car" deal, otherwise I wouldn't have been there) didn't seem at all surprised that that was the problem. To their credit, when all of their early attempts to find/fix the leak failed they did do the evaporator replacement under that warranty even though the time period had expired, since the initial problem was reported while the warranty was still active. And then they fixed the control door problem that they caused when they forgot to plug it back in when reassembling the dash.

 

The Auto AC place I use is a big shop been there 50 years i bet. The manager told me going in my 2007 probably has a leak in the evap they see that so often they stock the evap coil and the compressor also. G2 Prius is a very common car here.

I told him to take his time I have other cars so about 5 days into it I stopped by for an update and saw my car in one of the bays I checked it out and everything on the interior firewall was removed just a sea of connectors oh the humanity. Big labor. i told the manager take your time lol. Few days later I got the car back and was reminded what a fantastic ac system it has it was freezing cold had to turn the temp down to stand it.

That's the thing with ac leaks if there not leaking real bad and a very slow leak You hardly notice it slowly getting less and less cold over months and months until it gets warm.

 

Yes if I have that happen in a generation too I probably won't be taking the firewall down to that to do this I have too many generation twos I'll just move to another one actually I must be extremely lucky because none of my generation twos have had any air conditioning problems at all most of them that I get are all original from the original owners that have never touched the air conditioning system All I'm generally doing at 12:13 years is topping off that system with 134a till it looks right in the sight glass and then usually I'm putting the car out to pasture before there's any air conditioning major work ever even thinking about happening so I guess I've just been lucky. But sometimes it's just like that none of my Toyotas have ever had an evaporator replaced condensers yes compressors one or two not the electric so far these were in belt drive Corollas. So I'll just chalk it up to look and when my luck runs out no problem that's why I keep a few generation twos here at the house.