HOW TO: Charging your A/C air conditioner conditioning system at home.



I posted this thread on HONDA-TECH about a year ago. I spent a LONG time researching and verifying whats true and whats fake, and compiled EVERYTHING i know into this How To Writeup.

You can also check out the OVER 350 questions and answers posted on the original honda tech thread here....


After reading the threads posted here, I am sick to my stomach with all the false information. I will correct a few things.


I would like it to be known that my goal for this thread is to ANSWER EVERY POSSIBLE QUESTION ABOUT A/C REPAIRS for automobiles. This is going to be the all knowing, famous referrance for repair. So ask away! And I will do my best to answer or direct you to the answer.

On with the article...

From 1994-present, all a/c is r134a. 1993 and below is all r12. However, apparently SOME 1993 are r134a, according to feedback from some users.

I will explain to you IN DETAIL exactly how the air conditioning system works. Just keep reading on below.

If you need to vacuum your system out, GO TO AUTOZONE and rent a professional grade vacuum pump. They charge $200 up front. When you return it, you get ever dime back. Free rental service.



Due to the high volume of people complaining of how autozones near them dont rent vacuum pumps, I have decided to do our country a favor and rent out a vaccuum pump for a deposit plus 20 dollars. By the way, here is the part number for the vacuum pump at autozone....#90062 - This is the correct number not what I had listed before.

So what am I saying? I am saying that if you can't find a vacuum pump and you need one, I will go down to autozone myself and rent it. Then, you send me the deposit I pay ($213.00) plus shipping and $25. Yes, its a lot of money upfront. Yes, you will pay for shipping there and back, and I will make $25 off it. So you can expect to get a vacuum pump for anywhere between $35-$45 net cost. When you return the pump, you get the $213 deposit back. That equals $248-$258 approximate UPFRONT costs.

So, is it worth it to you? I don't know, But I am making it an option. Email, Call or PM me to take me up on this. And my name is Nate, if you don't know by now.


Well not really, but it sounds cool. What I'm saying is I have ANOTHER handy tool for rent! I just bought a professional grade ELECTRONIC LEAK DETECTOR by Bacharach...the TRU POINTE. This sweet ass device can detect a leak AS SMALL AS 0.1oz PER YEAR! Thats not a typo, 0.1 oz per year! Let me put this into perspective for you. An average size honda a/c system holds 22oz. That means a leak that small would take TWO HUNDRED TWENTY YEARS (220 years!) before the leak completely depleted the system. Meaning, if you have a leak, this will find it, GUARANTEED. You can view the specifications here:


Why do I say this with such enthusiasm...well one because I am a salesman and Im getting you hyped so you will rent it from me, and TWO...because it really works. I was able to find my leaks that were otherwise invisble to the UV dye I had previously tried. I had a couple leak drier connections (didnt put the fuckin o-rings in, now i wasted a whole batch of precious r12) and my nipples. Um, the a/c line nipples.

So, I am willing to rent this out, once again, for my cost ($150) plus shipping ($10) and a fee of $40. Why more? because find somewhere else where you can get PROFESSIONAL GRADE leak detection, that you KNOW is gonna be done right, for less than that. I already know the answer. You won't find it. Otherwise I would have done it myself. And let me tell you, I am smart shopper.

Recap, you pay $200 upfront, and you get back $150, and $40 of that original $200 goes into my pocket, for providing you this convenience.



If you have an r134a system, you can recharge it yourself. If you have access to r12, you can also, although you can not buy it at the stores. You need an EPA handling liscence to buy it legally, although if you are smart you can get a hold of it.

Proof that r12 owns. This is my vent temp while while ambient outside air is 100 degrees. 49 degrees vent temp at an parked idle. It will get down to 40 when driving and it is 95 degrees or less. Sick.


My lucky bottles of r12.


WHILE YOU ARE AT AUTOZONE, buy a "gauge manifold set" which looks like 3 hoses, red yellow and blue, and 2 gauges. Get the $70 or whatever is more expensive, because the cheap one doesnt have as many readings on the gauge. Buy the can tap and referigerant while you are there, or buy the can that already has the hose attatched to it.

I would like to mention to never buy the kind that has "stop leak" added. Only refrigerant, the proper oil, and UV dye is safe in your a/c system, regardless of what any advertising says.

Now there is really only 4 main things that are likely wrong with your system.

1. Moisture/air/low freon in the system. You can check this easily by looking at your receiver-drier. Look at the site glass on top of the drier. You will probably need to wipe it off to see through it. Now, if you see a million little bubbles, or a couple fat bubbles, then you obviously have either air in your line or you are low on freon. Check your pressure before topping off with freon. You do not want to overcharge. The safest way is to just drain the entire system and start from scratch, considering how cheap refrigerant is...where as if you overcharge and blow your compressor, thats gonna cost you $100 for a used on and several hundred for a new one, along with a new receiver/drier, new TXV/orifice tube, and if you are really unlucky, evaporator and condensor. Thats over $650 right there. Aparantly some AC systems don't have a site glass on the drier, so the only way to check is to check your low and high side pressures. Below 30psi LOW and 150psi HIGH is undercharged.

2. Your thermal expansion valve or TXV is not properly functioning. If debris got in your line, it can clog the valve, or it may just stop working. This is a $33 dollar autozone item you can replace while the system is open. When you open the system, you will also need to replace the receiver drier, because it absorbs moisture and will become saturated one you open the lines, making it useless. That is another $30 dollar item. Not to say that it instantly will absorb all moisture and become useless, however after if it is more than 2 years old you should replace it anyway, or if the drier was exposed to air for more than a day. Now if you suspect a leak in the line, you should hold off on replacing the drier until you fix the leak, unless you want to buy another drier while you open the line up and fix the leak.

If debris is caught somewhere in the line, it will cause premature expansion of the refrigerant. You will be able to tell this by checking the hot line for an immediate cold spot. Thats where the debris is located which needs to be flush out. When flushing you line, you CAN NOT flush through the compressor or thermal expansion valve. Most of the time flushing through the condensor will not clear the debris because it will just flow right past it.

3. Your compressor is bad. Unlikely though. If your pressure stays stable while the a/c is on and the pressure is within 25-50 cold side and 150-200 high side, normally that means its good. If the clutch spins with no grinding then that is a good sign.

4. You have a leak in your line and the system will not hold a charge. FIRST AND FORMOST, replace the valve cores on the high and low side nipples. I just found out last night I had a FAT leak in my valve core, and it turns out that was my only leak. If your system is already low or empty, you might as well replace them anyway and save money and a headache later. They cost $4 for a repair kit at autozone. It says its for r134a however it will work on r12 lines, even bycicles nipples.

So to recap what you will need to recharge your system:
1. Rent a vacuum pump from autozone.
2. Buy a gauge manifold set from autozone, 3 hoses with 2 gauges attached. Return them when done.
3. Buy saftey gogles. Protect your vision always.
4. If you have a leak, buy the valve core (high pressure and low pressure nipple) repair kit.
5. Buy refrigerant at autozone. Do not buy the kind with stop leak added, only regular or UV added kind.
6. Drain your lines of refrigerant. It is illegal to vent into the atmosphere, so use your common sense.


7. Attach the gauge manifold set to your high and low pressure nipples. Attach the vacuum pump to the middle (yellow) line. Open both the high and low side lines. Run the vacuum pump for 30 mins MINIMUM up to one full hour. If the compressor sounds like its seriously about to break, you can shut it off sooner, BUT NO SHORTER THAN 30 MINUTES. (A weak compressor may not have the power required to suck perfect vacuum, and will stress the motor.) Some may say less, but I say why risk under pumping when you can just let it sit a little longer.

In the first picture, you will side a r12 High Side adapter. Not all a/c systems will require this. Some r12 systems will have the proper fittings already installed. If you have r134a, then you would simply screw on the adapter pieces onto the gauge manifold.







FIRST, I will explain to you exactly how an a/c system works. The compressor will be the start of the process. So, the compressor first compresses AMBIENT TEMPERATURE low pressure vaporized (gas) refrigerant. (and this initial gas starts out at AMBIENT TEMPERATURE [ambient = surrounding temperature] simply due to natural tendeance for heat to balance itself among two platforms when the a/c has been turned off for a while. This low pressure gas will become a cool low pressure gas after it makes a few cycles through the system, thus the reason why your a/c blows colder over time.)

Once compressed it becomes a hot high pressure gas. Then this gas travels to the condensor and is cooled off (condensed) to a hot high pressure liquid. This was the first "phase change". It requires a LOT of energy for a substance to change phases. So when it condenses into a liquid, a LOT of heat is released.

The liquid refrigereant then travels to the drier to filter oil dirt and moisture, then to the Thermal Expansion Valve and becomes a cold low pressure liquid which causes it to absorb some heat.(Depending on the make of the car, it may use an orifice tube instead of a TXV, which does essentially the same thing. If it was equiped with an orifice tube then rather than passing through a drier previously, it would go straight to the orifce tube then to an accumulator after the evaporator which serves as a dirt and liquid filter to prevent liquid refrigerant from traveling to the compressor and potentially locking it up.)

Now that its a cold low pressure liquid the boiling point has been reduced significantly. It now travels through the evaporator which is where it absorbs its heat from and is also where the second phase change occurs. When the refrigerant reaches its boiling point halfway through the evaporator, it requires A LOT of heat for this phase change to occur. Thus the absorbtion of the heat from the surrounding air making it cold, and is then blown at your face as conditioned air! Now that the refrigerant has absorbed a LOT of heat, its a cool low pressure GAS and heads back to the compressor and repeats the whole cycle!

Now....Air in the system can lead to higher than desired pressures in the a/c lines, which could falsly activate the high pressure cut off switch and turn off the compressor when in reality your compressor hasnt been running long enough to cool you down at all! Air-Air is also a VERY poor heat transfer platform. So when it reachers the evaporator, its just wasting space and doesnt actually remove any heat. However, Air-Liquid is a GREAT heat transfer platform, hense why your radiator has LIQUID flowing through it, and same with your evaporator and same with your condensor. So this is ONE reason why we pull a deep vacuum.

Moisture in the system can form corrosive acids when mixed with refrigerant or oil which will tear up your a/c system over time. It can also freeze and cause a block in the line considering its freezing point is MUCH higher than that of refrigerant. This is the OTHER reason why we pull a deep vacuum. To lower the boiling point of water and make it a vapor which can then be sucked out with a vacuum pump.

On with the vacuuming process..."

(For this section, when I refer to "psi" I am really refering to "inches of mercury" or "inHg" which is the proper measurement for vacuum)

Once the vacuum has completed, CLOSE BOTH VALVES BEFORE TURNING OFF THE PUMP, or air will be sucked right back in the system and you will have to repeat. Your vacuum should be close to -29.92 psi. Now, it likely will not be this close, because that is perfect vacuum. But the closer the better. I got mine to -28.3 psi. If it only reaches -15 psi. then you likely have a leak somewhere preventing deep vacuum and your a/c system will NEVER blow cold with that a shallow vacuum due to the excessive amout of air and moisture left in the lines. I will repeat that. YOU MUST HAVE A DEEP (CLOSE TO -29 PSI) VACUUM FOR YOUR AC TO BLOW COLD. Vacuum lowers the boiling point of liquids, so at -28psi water will boil at approximately 10 degrees. Remember, if vacuum never gets deep enough, the water will never boil and be removed from the system. And we already know why air and moisture is bad for our a/c system.

Keep the gauge manifold attached with both valves CLOSED. Now you want to keep the lines up there to check for any leaks in the system. I let mine sit for 24 hours to check for any leaks. If you have a leak, the pressure will begin to stablize towards 0psi. Now its very possible that you have a small leak that lasts several months before fully depleting the system. There is another way to check for leaks. If you bought the UV dye kind of refrigerant, then you can check with an UV flashlight once you finish the charging process. You can also buy an electronic leak detector to check. It beeps when it senses refrigerant and detects as small as 0.1oz per YEAR. I do not know how small of leaks UV dye will show.

Now. If you have not changed any parts then you will still have oil in your line, so you do NOT need to add any. You do not want to overcharge with oil, or damage and insufficient cooling may occur.

Now with the valves CLOSED, unhook the middle line which goes to the pump and hook up your line that goes to the can of refrigerant. THIS NEXT STEP IS VERY IMPORTANT. With the refrigerant line CONNECTED and the valves CLOSED, open the can tap valve on the can of refrigerant. Now refrigerant is pressurizing the line. With your saftey gogles ON, press and hold the pressure relief button just above of the middle line's input connection. This allows refrigerant to fill the line. Hold this for about 10 seconds. This removed all AIR and MOISTURE from the yellow line and fill it with refrigerant. You do not want to add what you just spend an hour removing right back into the system.


Now that the line has been purged of air and moisture, you are almost ready to begin charging the lines. Turn your car ON and turn the a/c to max cooling max fan. Your compressor will most likely not turn on due to the low pressure cut off switch, which prevents damage to your compressor when the pressure is too low in the line. Now open the can top on the refrigerant can and open the LOW SIDE (BLUE) valve on the gauge manifold set. ONCE AGIAN, THE LOW BLUE SIDE, NOT RED. If you charge on the high side, you risk blowing the can of refrigerant up. Think about how much pressur 200psi is on a baby can of refrigerant. Now it will take about 30 minutes to an hour to fill the system with refrigerant. You might need to use two cans of refrigerant. If this is the case, when you are ready to switch cans close the blue low side tightly. Remove the empty can and attach the new one. NOW DON'T FORGET TO PURGE THE LINE AGAIN. Now repeat the process until the system is charged properly.

For those of you who are just a little low on refrigerant, you can top off your system if the leak is not major. You deside whether the leak is over a long enough period that it is worth it to simply top off and let it leak out again. To me, a 3 year long leak would be worth it to top off. Its easy enough to fix a leak.

To top off your ac, you do not need a gauge manifold if you are careful. Hook up the bottle straight to the low side line. REMEMBER TO PURGE THE LINE. To purge it without a purge valve, open the can so refrigerant is flowing out of the line. Now just screw on the hose while refrigerant is flowing out. Now you are safe from contaminating your precious time-invested a/c system.


Each a/c system takes its own amount of refrigerant. It's also very hard to judge how much of the can you have used, so be smart and pay attention so you dont overcharge. I highly doubt that the using the full can will be the exact amount you need.

WHEN YOU ARE FINISHED SERVICING YOUR A/C, MAKE SURE TO PUT THE CAPS BACK ON THE NIPPLES. If you dont have caps, GET SOME. The valve cores do not always seal properly. I just replaced mine and it still leaks a little bit some times. The cap will 100% seal them from leaking.


I hope this guide helped anyone who read it understand how a/c systems work and gave you enough knowledge so you can at least charge you system at home. There is no reason to pay a shop $100+ bucks in labor plus the cost of refrigerant when you can do it at home for ONLY the cost of refrigerant.

Here are a couple of websites that have a lot of great info on them about a/c's.

Stay cool.



Since you are probably wondering now...I will update my post.


1. First, go buy flush at autozone. DON'T use regular soap, detergent or degreaser. The resedue left behind is not compatible with a/c oil or refrigetant. A/C flush solvent residue IS compatible with oil and refrigerant, so if any is left behind its no worries.

2. Rent an a/c flush gun from autozone. This just makes the process 8000 million times easier. If you cant find one, you could make one. Its basically a can with a charging input at top where you connect the compressed air source, and a removable peice at the top where you pour solvent into, and an output line coming out of the bottom where the pressurized solvent flows out. Otherwise, if you are really ghetto, you could get a funnel and pour it in the line 1 oz at a time, shoot some air through, and repeat.

3. If you have a flush gun, pour solvent in, hook up compressed air that will supply at LEAST 90PSI at 2.5 cfm. Ideal is 135psi constant, max 150 psi. Any less than 90 will not blow the solvent through efficiently.


4. Unhook the lines at either the compressor. Then unhook the opposite end of the line and have a little bucket there to catch the flush material. So example. You want to flush the high side. Start at the compressor output line, then it will go through the condensor and come out of the drier fitting. (Remember, cant flush through the drier.) Then, start again at the drier output, and finish at where the expansion valve would be. Either do that, or take the TXV out, reconnect the lines, then flush from the drier output all the way through the evaporator then out the input line for the compressor.

Start flushing. It will shoot through the lines. The solvent is clear. If the solvent comes out BLACK and thick then you need to keep flushing with more solvent until it comes out CLEARISH and THIN. (It came out literally like melted chocolate when I flushed this dude's ford explorer.) The whole flush process takes about 30 minutes to an hour depending on how many times you need to flush it.

Its good to have a hand around to hold the compressed air line on the top of the flush gun while you hold the flush gun line in the a/c lines. Its stupid because you cant just screw the compressed air on the top, you have to hold it like pumping up a bike tube. It sucked to hold both by myself.

Once you are satisfied with the color of the solvent output, continue to flush with PURE AIR for 5-15 minutes, or until mainly air comes out. Be aware that most of the time, the solvent will be coming out as mist, while some will be dripping out in your bucket. It didnt kill me to breathe it, so i assume its non toxic. Also, when you first start to flush with a full can of solvent, BE SURE TO HOLD THE FLUSH GUN LINE UP TO THE A/C LINE FIRMLY, OR IT WILL ALL SHOOT RIGHT BACK OUT AT YOUR HAND.

Have fun.



Upon successfully recharging my second a/c system of my life, mine, my vent temp now blows at 50 degrees when ambient (outside) air is 110.

At 95 degrees and below, my a/c will max out at 40 degrees vent temperature (verified with a gauge) , which is when the compressor cycles off to prevent frost/ice from forming on the evaporator coils.


And by the way. If anyone wants to send kind donations, do so with paypal at

Modified by drumminforev at 11:19 AM 8/30/2006


Setting the standard
Feb 22, 2007
Central Florida
You can speed up the filling process alot quicker by putting the can on a hot engine part :)

In the process of motor swaps, upgrades, a hose breaking.. I think i've done this 5 times in the last year to my car.

It's going to be #6 in a week while i remove my hard low side line and have the nipple moved because its 1" from the turbo and I cant fill it.


Yes true. I always just get a big cup full of hot water and it speed it up by about DOUBLE.


Yeah that surely couldnt have worked to well. First of all, the odds of you actually removing all of the air is 0.2%. you might have displaced some, but not anywhere near vacuum

and the fact that you have no vacuum is probably limiting the cooling ability by 10-20 degrees.

and since you didnt vacuum it, that means you have moisure in your lines, and over a few years that will absolutely destroy your a/c system, along with limiting its cooling ability.

I think its too easy to just hook up a vacuum pump and do it right and spend 15 minutes instead of only 5


Setting the standard
Feb 22, 2007
Central Florida
The a/c compressor on my SC300 never seems to cycle, it just stays engagued with the AC turned on. Is that normal? Or what could cause that? It's been pulled with a vacuum machine for 1hr, and filled to the correct amount


Arizona Performance
Nov 14, 2005
Mesa, AZ
I worked for GM between 91 and 95 and R134 was mandated By the EPA to be used in all vehicles manufactured for the 1994 model year. All the manufacturers knew about this more than 2 years in advance. Some manufacturers knowing this was coming just switched over as soon as they could especially if they had a new model year change over or if they were particularly quick on their feet when it came to engineering and design. Of note, very few Domestic manufacturers compared with the imports were able to release vehicles equiped with R134 A/C systems before the 1994 model year.

Why didnt you hear a big stink about all of the extra costs? Because your government had been convinced by the earth Nazis that R12 was bad for the environment. The truth is R134 in its original formula was a carcinogin (not sure if it still is). Which is worse that 12-30 ounces leaking out in an automotive crash "IF" the system is ruptured in a car accident, Or Cancer.

Why didnt you hear about all the expensive changes required to convert an entire industry from one standard of cooling medium (R12 Freon) to the newer less effective more expensive more caustic R134? Because the EPA/government gave huge tax incentives for tooling change over to all the automotive manufacturers and then charged you the consumer again for any more additional costs for an inferior product.

Now look at the costs for a 12oz can of each, the whole industy and your government and eco nazis screwed an entire country on your dime, and almost no one ever heard of it.

Ok I will get off of my soap box now.

Just an FYI.

Sorry for the rant hope it was somewhat informative.


RIC. so it stays on always, but does or does not blow cold, and how cold? It doesnt mean its bad that it doesnt cycle. it might be perfect but just never reaching the low temp cut off switch. need to know the vent temp tho


i dont see how they couldnt have it. cycling system...the evap would for sure freeze over if it didnt have it. but it doesnt mean its supposed to always cycle. like he said unless ambient temp is low or you have the fan setting too low to remove all the temp from the cold refrig


Setting the standard
Feb 22, 2007
Central Florida
Ambiant air temp is usually in the mid 90s, and i dont have a vent temp reading, but it gets COLDDDDDDDDD. Even in a 90 degree day in traffic, I can't have it on full cold.

Doing more research, looks like my car uses a TXV system, not CCOT. So i guess it's working correctly because it's not supposed to "cycle" unless it's below 32* F and then it will shut the system down to prevent freezing.


creepy-ass cracka
Jul 11, 2005
Redacted per Title 18 USC Section 798
Exactly. I don't recall Toyota ever using CCOT so as long as the TXV is controlling superheat the comp shouldn't cycle. Not saying it won't if the ambient gets low, the fan is low, or something goes wrong but it normally won't. It's especially unlikely to do so at a 90 ambient.

Drummin: CCOT systems run with flooded evaporators so they need to cycle. A TXV system operates differently. By sensing the temperature of suction line and controlling superheat evap freezing is normally avoided.


Official SM Expert: Motor Oil, Lubricants & Fil
SM Expert
Feb 10, 2006
Valley of the Sun
Here's the TRSM locations for the A/C parts on the Mk III:

Location of the high/low charging valves:

The low side valve is on the compressor...the high side valve is actually here on my '89:

Location of the expansion valve (TXV):

It's on the top middle of the evaporator...I'm thinking this will be a royal PITA to get to get to ;)

Manifold Gauge readings:


creepy-ass cracka
Jul 11, 2005
Redacted per Title 18 USC Section 798
I'm not familiar with the SC system so I'd have to look at it. They may be doing the heat pump thing. A lot has changed in MVAC since the MKIII came out. Many systems are now using variable displacement compressors for example. I'm 609 MVAC and 608 Universal HVAC certified but since I've never done it for a living it's hard to keep up on all the changes.


New Member
Aug 27, 2005
Southern California
Drum Awesome write up, your're the first person Ive ever seen that put allot of spotlight onto the Vacuum FIRST before the Re-charge, Thanks for the Writeup. I at one time was in Aircraft Refridgeration.


Supramania Contributor
Mar 30, 2005
Arz, a couple notes for you...

R-134a (tetrafluoroethane) is quite different from R-134, which is not effective as a refrigerant. You can read the safety info on R-134a at Wikipedia:

As for R-12 (Dichlorodifluoromethane), it is an incredible ozone destroyer once it gets to the stratosphere. Since the stuff has a life of about 100 years, it has a long time to get up there. Ozone depletion means far more UV rays getting down to earth, and that means an increase in skin cancer.

More info on refrigerants from wikipedia here:

If you'd like proof about the ozone depleting power of R-12, look no farther than the Montreal Protocol, has been ratified by 191 countries so far.