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Charging methods and accuracy

uunfews on Wed August 13, 2008 3:37 PM User is offline

Year: 2001
Make: Honda
Model: Civic
Country of Origin: United States

I know the perfect and correct way to recharge is to evactuate out all freeon and recharge with the proper amount per the auto manufacture's spec.

But what I wanted to know is has anyone ever measured the accuracy of the old method of topping up on refrigerant using the traditional method of using the manifold gauge and thermometer at the center vent to see how far off it is from the auto manufacture recommended method of full evac/recharge. That is after topping off a system have you evacuated then measure the freeon to see how far off it is from the manufacture's recommended amount. Is it off by 10%, 20% ? And is this overcharged or underchaged? Or is it neglible like less than 5% or 3, 2, 1%?

Thanks all.

Newbie wanting to learn how to fix his 01 Civic AC in this freaking hot Dallas TX area.

iceman2555 on Wed August 13, 2008 9:01 PM User is offlineView users profile

MACS did a article several years ago concerning this topic.....have to see if I can locate it. Although it was not a true' study' as set forth in this post, it did contain some very important information.
What you state and consider to be 'traditional' to me is simply the 'old' way to service and A/C system. The down side of failing to change with a complete change with the newer more accurate service procedures is, unfortunately, unsatisfactory repairs or even, this we see more and more, an increase in failed parts....newly installed...esp compressors.....and these failures are normally attributed to warranty issues.

The automotive A/C system of today bears only a slight resemblance to the systems of yesteryear....yes..true they have the same parts...both still transfer heat....however, the modern system is much less tolerant to undercharging...over charging....lack of engine cooling.....condenser restrictions....the system of today requires more specific service procedures as those of years gone by. Recharging is one of those more specific aspects. This does not even take into effect the change from a TXV to CCOT system.....critical over charges....flooded evaps....and other changes in the systems.

Most HVAC compressor engineers will agree that the number one cause of compressor failures is a lack of lubricant. One must remember that the compressor is a motivator for system operations. It must accomplish several operational aspects to maintain system must move refrigerant...lubricant...and this is a serious that 134a is not totally miscible with either PAGs or POEs....elevate pressures/temperatures enough to maintain certain performance criteria.....and often must accomplish this is a system that was not prepared properly for its installation .
Along with this agreement of the cause of compressor failures...OE and after market.....a system that is undercharged by 10-15% may suffer serious compressor damage....or more that likely...a complete compressor failure....tie this to other changes in the modern system.....this failure may equate to a total system replacement.

Recharging....correct and a major cause of compressor failures. Often when compressor returns are evaluated for possible failure issues....we see many units that are locked...burned clutches...or notice of 'excessive noise'. When these units are inspected....there is clearly indications of lack of lubricant within the compressor....discharge ports that indicate movement of lubricant from the compressor...but suction ports that are 'dry as a bone'. This is a good indicator of an undercharged system.....the compressor is able to push the charge refrigerant/lubricant from the compressor....but because of the undercharge condition the system lacks the ability to maintain this flow of lubricant and the compressor starves for lubricant. Even with OE failures...this issue is often mimicked.......the number one failure of OE compressors is a locked/noisy unit. When the OE compressor is removed from the vehicle and lubricant is drained.....(part of the installation procedures)...the compressor drains no to very little lubricant.

If one looks back as the 'traditional' (older) systems....the recharge rates on most of these systems exceeded 3 lbs....48 oz or more. This 10-15% undercharge was not as important as it is today with a system that requires only 16 oz...or less. The +/- allowance was sufficient to allow for 'topping off'. Also keep in mind that many of these older systems utilized a compressor that was 'sumped'....maintained its own lubricant. The compressor of today...actually the R4 was the a non sumped compressor...they are totally reliant upon refrigerant to maintain that required flow of lubricant. The variances were such that a system could be 'topped off' using pressures...and vent temps as a tool. These variances simply do not exist today.
An R12 type condenser was almost impossible to become restricted....and could be cleaned easily with chemicals available during that period. A change to the more efficient condensers of the modern system does not share this same characteristic. Charging by pressures is an 'inexact' procedure....note recognized by most top notch techs. They rely on the exact charge rates of modern charging stations to remove this very important variable from the diagnostic procedure. Combine this with the idea of what an excepted pressure should be at a given point. This is a learned is one that has lost much of its reliability because of several conditions. One of the most important aspects of simply using pressures is the change in service port locations.
Changing high side ports from the liquid line to the discharge port is a significant change in the system....and may result in many erroneous computations.

Charging to a 'low vent' temp has always been another 'inexact' procedure.....under certain heat loads....and undercharged system may actually indicate a 'cooler' vent.....keep in mind that 10-15% this method also lacks some validity.

All these aspects of recharging become much more relevant when 134a is used in a 12 system....this change all but negates the 'traditional' pressure/temp method of recharging.

When traveling thru out the US....the shops that have the least amount of warranty returns....that exhibit the most professional service.....all have forgone the 'traditional' manner to 'top off' as a service procedure. I was in a shop recently...the 'tech' was in a 'fit to be tied' mood....hated auto A/C.....system were trash....134a sucked.....nothing was like it was....should bring back 12.....he was 'servicing' a late model GMC truck.....and could not get the pressures 'right' and the darn thing would simply not cool.....must be the damn truck. Never mind that he had 'topped off'....several times....released who knows how much 134a.....all in an effort to make a system conform to what he perceived as 'good' pressures.
A simply recover/recharge eliminated all these problems and then pointed him to a potential fan clutch issue.

All in all....keep the 'traditional/older' methods in mind...but change the method....move ahead into a more reliable....more accurate method of A/C service....use of the correct and proper equipment to insure that the system is completely and totally recharged to OE specs.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

befuddled on Thu August 14, 2008 12:40 AM User is offline

Someday, when you are looking for a good chuckle, I will tell you my experience that made me the AC guy in the shop.

In the mean time let me say that I am the least experienced and capable 134a guy here. But you might be interested in a recent experience. I did a full charge on a late model foreign car. Nothing remarkable about it. It called for something like 24 ounces of R134a. I used two 12 oz cans, right side up, so vapor charge in the low side port. It took awhile for the system to absorb it all, maybe 20 minutes or a half hour. There was not much in the way of a good vent temp until I had something over 20 oz in. Then I could see significant cooling. I got my lowest temperature at about an ounce short. As I added the last ounce, or thereabouts, judging from the ice on the outside of the can, the vent temp rose slightly, a degree or two. And the system seemed reluctant to swallow the last ounce, but it did. That tells me that this particular system is pretty sensitive. And probably precisely engineered for performance.

I am not so sure that R134a systems are inherently temperamental as they are designed on the edge for cost of manufacture. Can't spend money on a extra ounce you know. On a few hundred thousand units it adds up. With computers, the engineers can know exactly the volume of the inside of the AC system in seconds. So they can calculate exactly how much lube and refrigerant the system needs. And build it to exactly match the car they are putting it in. Want to figure that out with 1960's technology? And I didn't mention fluid dynamics. Those equations were virtually unsolvable when I was in school.

NickD on Thu August 14, 2008 8:27 AM User is offline

This is somewhat of a system dependent question, in the manual of say my 65 Buick with the constant running compressor and the POA valve, was recommended to use a charging station, depending on the amount of bypass, couldn't really rely on pressures to determine the state of charge. In my Supra manual, they actually recommended using a vent thermometer and pressure gauges giving a full chart of preferred pressures and vent temperatures versus ambient temperatures and RH values.

In more recent Ford and GM manuals with the CCOT system, they recommended dumping in a fixed charged, but their vent temperatures and pressures varied all over the board, dependent on production variations. Kind of ignored that and set pressures to the mean values to get the best performance. Not sure about these new variable displacement compressors like the V-5 and 7, haven't played with them yet, but should be like the old POA.

Actually with the old POA and STV systems got by with hooking up the gauges, tank to yellow and adding charge until the outlet equaled the the inlet temperature on the evaporator, and could feel pulsations on the inlet, added charge until those pulsations disappeared just looking at the gauges to make sure the pressures were not going through the roof, still have a pressure relief valve. That resulted in great ice cold vent temperatures in those good old systems. Time is also a factor if doing this professionally, if that was the case, would get a charging station, it takes extra time to charge by pressures and vent temperatures. The accumulator or receiver also act to provide a fudge factor for a little extra reverse, yet another indicator of charge in the system when you can see that moisture line. Gauges are always good, something may be wrong.

When playing with pressures have to keep in mind that in extremely hot environments you tend to undercharge that will cause excessive cycling when the temperatures dip or vice versa, will tend to over charge if the temperatures are low. So I like to do this on a 90*F day that is a good compromise, but really do not have control over the weather. In this instance, best to charge by recommended weights and hope for the best because all days are not perfect.

Edited: Thu August 14, 2008 at 8:41 AM by NickD

uunfews on Thu August 14, 2008 2:38 PM User is offline


I appreciate all your responses. Actually I was checking' up on the advice of a shop locally here which offer AC servicing and mentioned to me that they top up using the 'traditional' method if upon checking that the freeon is low. When I brought up the subject of that being against the recd' OEM procedures he said that is not true and that the old method is the way that has always been done and that they can get it to within +/- 0.10 of an ounces. Now I find that hard to believe hence I asked here to see if any testings have been done to compare against the 2 methods. This shop also mentioned that they have a evac/recharge station but it would be 170 bucks if I want it to be done the OEM way. Was unusual to see they got the machine but wouldn't do it by the book.

I am just gathering info to contemplate if I can do the AC fix myself or not since the quote I got was outrageously shocking to say the least. My compressor is making a knocking/rattling noise whenever the clutch is engaged ONLY but still blows cold air...checked temperature the other day at 84 ambient and 44 center vent and another day at 92 ambient and 42 center vent. I been reading numerous site and it's suggested that I could have air in the system/excessive oil/or an overcharged or undercharged system. I don't know if the system has ever been worked on since I bought the car used at 84k miles.

Was thinking that if I attempt to DIY then get myself a digital scale/placing the freeon can on the scale platform to weight the freeon as it leaves the can. What do you think? Will this work? But then what about the freeon that is left in the line once I shut off the valve at the top of the man. gauge. Will this make the system short or undercharged?

Iceman: I like to see whatever studies you have to see how far off it is. As a matter of fact anything to compare the 2 methods.

PS: Anyone got some info or diagrams on all the locations of the AC components/switches/etc...I dread the idea of replacing the expansion valve since I heard that it is only accessible inside the car only am I correct? Better yet any link to the service manual for my car???


Newbie wanting to learn how to fix his 01 Civic AC in this freaking hot Dallas TX area.

Edited: Thu August 14, 2008 at 2:45 PM by uunfews

mk378 on Thu August 14, 2008 3:09 PM User is offline

How long have you had the car? If the compressor used to be quiet but has gotten noisy without anyone doing anything to the system, it is probably the compressor itself starting to come apart inside. Needs to be replaced now as it will shed metal debris into your system which are hard to clean up. The cause of such failure could be too little or too much oil, but it is too late to correct now.

I think the 2001 was the first one Honda made with the evaporator built into the dash instead of a separate removable evaporator case. There will be a block type expansion valve mounted just on the engine side of the firewall. The expansion valve can be easily removed for replacement or flushing the evaporator.

NickD on Thu August 14, 2008 3:14 PM User is offline

Your car does have a sight glass, on a warm 85*F day, door open, engine running at 2,000 rpm, AC on, blower at max, this glass should be clear or a bubble now and then. R-134a can be slowly added till that glass clears, but also good to check for any oil stains any where on the AC system.

Last Honda I looked at, the compressor attaching bolts to the block were falling off that caused quite a noise, could be your problem as well, look at it.

iceman2555 on Thu August 14, 2008 4:20 PM User is offlineView users profile

The compressor noise issues is probably related to a possible undercharged...esp if the system has NEVER been serviced and the mileage exceeds 84k miles. It is also possible that the system has been serviced in the past....but because of possible undercharge in the past...the compressor has suffer some internal damage. The unfortunate part of this problem...the resultant debris produced by the internal damage may be restricting the flow of refrigerant and lubricant and the result is farther internal damage.
Servicing the system....evac/recharge will aid in possible increase in cooling efficiency...however, the noise issue may or may not be solved.
As against all the rules known....if the compressor is noisy...but the noise in not objectionable....why not service the system.....evac/recharge and run it till the compressor gives up the ghost. Heck it could operate for a very long period of time.
The process of repair would basically be the or then....a replacement compressor....a good cleaning.....evap TXV....rec/drier/filter....and a suggestion to replace the condenser. Serviced a neighbors Honda several weeks ago.....did not want to spend the money for a new system...was thinking of trading the car......yeah....yeah....yeah.....heard that before....but still...wanted the system serviced....did the recovery/recharge...added an oz of lube (not always necessary....just that part of the 'traditional' method that remains).....and the result was a somewhat less noisy compressor.....acceptable vent temps.....and someone who got exactly what they wanted.
The shop in question....a +/- .10 that is fantastic.....heck...that is even better than the best recharge machine on the market today.....this is outstanding.....what are the rest of us gonna do....heck these guys are in the top .000000000000000001 %....we should all be seeking their exalted knowledge....and not to mention try to scale the heights of their ability......boggles the mind!!!!

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

Edited: Thu August 14, 2008 at 4:21 PM by iceman2555

uunfews on Sat August 16, 2008 1:43 PM User is offline

Iceman ,

What do you think of my method of using a digital weight scale to meter in the refrigerant???

MK378: Thank you for giving me the info on the expansion block being accesible at the firewall side. You gave me some hope about my chance of success if I decide to tackle this myself. I dreaded it being under the dash. Trace the big and small pipe to the firewall being under the cruise control that deadend into some plastic but havent seen any block type exp valve yet...?????? Help please.

I also don't know any type of servicing history of the car's AC having had the car for only a month and the previous owner saying he knows of nothing either since it was his kid's car.

Newbie wanting to learn how to fix his 01 Civic AC in this freaking hot Dallas TX area.

Edited: Sat August 16, 2008 at 9:00 PM by uunfews

iceman2555 on Sat August 16, 2008 5:38 PM User is offlineView users profile

Along with the recovery/recharge equipment used in the shop, we also use gauge sets/digital scale/heater blankets to service vehicles. The heater blanket allows for increasing pressure within the refrigerant container and allows for complete charge introduction without engaging the compressor to complete the charge process. They are well worth the investment, esp if purchasing the scales and perhaps planning for some future expansion of A/C service.
Keep in mind that the expansion of services, actually, any type of A/C service, legally requires the use of specific equipment. It is illegal for anyone to knowingly vent refrigerant, 12 or some others...but these are the ones we are dealing with here.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

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