First off let me educate you on what Freon is. Freon is a trade name, kind of like Mayfield is to milk. More accurately, it is referred to as refrigerant by all air-conditioner technicians. And, there are about a dozen different types of refrigerant.
While both of them are responsible for absorbing heat, they both do it in completely different systems for completely different reasons in completely different ways. Coolant is a liquid and comes in a bottle and is not pressurized until it is put in a radiator with a pressurized radiator cap. The refrigerant is a gas until it reaches either 40° below zero or about 250 pounds of pressure; whereupon the refrigerant gas then becomes liquefied.
I know that's technical, but when someone calls up and says to me or one of the service writer's "I need some coolant"... That is when the questions from us begin. Typically, we are going under the assumption that they see a green or red liquid under the car and the vehicle is experiencing an overheating problem.
Not a thing to do with them sweating their butt off while going down the road.
The automotive cooling system and the automotive refrigeration/HVAC system are completely different animals and the only common area between the two is typically used by the engine control module to determine whether or not it is going to allow the air conditioner to come on based on coolant temperature. If the car has overheated due to a cooling system issue, the engine control module will not allow the air conditioner to come on when temperatures exceed about 250°F. Other than that, there is no link between the two.
In automotive use right now there are only three types of refrigerant or Freon, and two of those are about as rare as hen's teeth. So, this discussion is going to be about R-134A.
R-134A is the refrigerant which replaced R-12 in 1996. The R-134A is less destructive to the ozone layer than the old R-12 was.
The next is the stuff that's going to be in all of the automobiles by about 2022. It is called R1234yf refrigerant. And boy is that new stuff ever expensive! But enough with this technical stuff.
So it is based on your car, the age of your car, and if your Japanese car has had a complete refrigerant change to the R-134A. It is most likely R-134A but without information on the last time your system was charged your just taking a guess and could potentially do more damage than good.
Every Japanese automotive air-conditioning system I've ever seen in the past 44 years is going to lose refrigerant over time.
How much it loses is the hundred dollar question.
The refrigerant can leak out in a couple of different places. It can leak past the seal in the compressor. It can leak past the charge ports where the system is serviced. Or it can leak past any of the O-rings which connect all of the components.
But, it's going to leak a small amount over an extended period in even the best conditions. What makes this such the potentially costly problem is that when it leaks refrigerant, is also leaking the lubricant which protects the moving parts of the compressor. And that will cause the compressor to fail. And sometimes when the compressor fails, it will damage/clog up other components, typically the condenser.
The condenser is that "second radiator" that is in front of the other radiator. And when the compressor and condenser fail, it can have a snowball effect.
So how often you need more freon/refrigerant can vary from vehicle to vehicle. Though having it tested by a professional can help you gauge where you currently stand and if it is time. If your car is blowing warmer air then normal, it is most certainly time.
Now if you consider adding your own Freon/refrigerant you must remember, too much refrigerant in a system will also cause problems. If that extra can of refrigerant is added without the correct ratio of lubricating oil, that can have the same disastrous effect as running it low on refrigerant and oil.
Excessive refrigerant- even with the correct ratio of oil will cause the system to run at much higher than designed pressures which also leads to component failure. Quite a balancing act here, don't you think?
So, you still have this notion to go to the parts store and grab a can of "Freon" (because your uncle/brother-in-law/want to be mechanic friend down the street thinks it's a good idea) and have a whack at it yourself, let me warn you about one last thing.
Most of those cans on the store shelves have this nasty little ingredient known as "stop leak" added in the can.
When this stuff is introduced into your air-conditioning system, it also has the capability of wreaking havoc on your system. There are a bunch of very tiny holes in a bunch of different components in your car's air-conditioning system that doesn't need to be stopped up.
If they do get stopped up, your air-conditioning won't work- no matter how much or how little refrigerant is in the system.
This stuff is so bad that every single automotive manufacture I am aware of has all sorts of written warnings about this stuff and how it will void any and all manufacturers warranties on anything and everything related to your air-conditioning system if this stuff is found when a part is submitted for a warranty claim.
I think that pretty well spells out why that stop leak stuff should be kept away from all automotive refrigeration systems.
So, does your Japanese car need more Freon/refrigerant? Here's my best advice: bring it to us! We have the training, the tools, the chemicals, the know-how, and most importantly, the ability to accurately determine what it's going to take to have cold air coming out of those air-conditioning vents in your ride.