Automotive Air Conditioning Information Forum (Archives)

rastoma on Wed June 08, 2011 9:07 PM

Year: 2003
Make: Chrysler
Model: Town & Country
Engine Size: 3.3L
Refrigerant Type: R134a
Ambient Temp: 90
Pressure Low: 35
Pressure High: 110
Country of Origin: United States

The current readings are fluctuating because I know there's not enough R134a in there yet. I know it will need less than a can so wanted to know pressures before adding that last can to it.

TRB on Wed June 08, 2011 11:36 PM

I have no pressure listings on this one.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

iceman2555 on Wed June 08, 2011 11:44 PM

The correct operational pressures of this system are those pressures derived from a fully charged system. The recharge should be completed utilizing the correct recharge equipment that is able to charge to within 1/2-1 oz of OE specifications. Charging by cans and seeking a perceived pressures is a very good method to insure system component failure.

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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

rastoma on Thu June 09, 2011 9:38 AM

If that's the reply you give everyone asking for help such as pressure numbers, then there's no need for this forum. There would be no need to help anyone or provide any information at all. There should be a main page that says this is not a DIY forum take it to the shop and use CORRECT RECHARGE EQUIPMENT.

But yet the majority of the information offered is aimed at those who are doing this work at home.

I have CORRECT equipment, other than using 12oz cans instead of a 30# canister.

So you just told me that the correct pressures are from a fully charged system. And in order to get a fully charged system you must fill it to OE specifications.

So that is EXACTLY what I was asking.

So if someone else would be so kind as to tell me what pressure readings will show on a fully charged system I would much appreciate it.

mk378 on Thu June 09, 2011 12:17 PM

The manufacturer's specification is to fill it by weight. If the air gets cold and the high side is reasonable for your ambient then you're done. You can assume each 12 oz can will deliver 11.5 oz of net charge, but it's much better to use a 30 pounder and a scale.

iceman2555 on Thu June 09, 2011 1:51 PM

A highly accepted misconception is that one can accurately charge a vehicle utilizing a 'perceived' acceptable pressure range. This is not now.....nor never has been an acceptable method of charging a vehicle. This is simply a 'short-cut' derived by technicians over a period of time. Pressures are a method, not always the best, the determine the operational conditions of a 'FULLY' charged system. Unfortunately, this does not always work in the reverse....using a 'perceived' pressure as indication of a fully charged system. There various operational conditions that have an effect on this.

OE test specifications are based on a fully functional engine cooling system, a system with no restrictions, the correct amount of lubricant, and most important...a FULLY charged system. Even if we go back to the 'old days' when a great deal of this 'charge to pressure' procedure originated, technicians should have been utilizing the correct procedure of charging using the graduated charge cylinder to determine a fully charged system. Over a period of time, most tech's determined that at certain charge rates....certain pressures were obtained. Following this 'advancement' it became a standard procedure to charge to this or that pressure was determined. Yet even in this time, this procedure was still 'hit and miss'. The 'saving grace' of this time was that all of our compressors were designed and manufactured with a true sump type lubricating system. If a system were serviced and an acceptable vent temp and system pressure were derived, the repair job was considered a success. The system could actually be undercharged and still the compressor would maintain itself due to a storage of lube within the compressor. The introduction of the 'sump-less' compressor in the mid 70's presented an entirely new issue....the use of refrigerant to maintain the flow of lubricant thru out the system.

The number cause of compressor failures is lack of lubricant or lubricant flow to the compressor. The major cause of this lack of lubricant flow is lack of refrigerant (charge) issues or a restriction within the system.

Fast forward to todays system and the entire system has totally changed. The reduction of refrigerant charge in a modern system of 5-10% can and will contribute to a failure of proper lubricant flow to the compressor. The amount of undercharged may not be noticeable to a 'pro tech' and can be assured that a 'DIY'er' will never see this problem. Back to the issue of 'what pressures are good'....those 'good' pressures are derived from a fully charged system....fully operational engine cooling system....and operational ambient temps and humidity. If one were to poll 100 'pro techs'....one would probably be supplied with 100 different pressure ranges. To properly service a system this is a non acceptable method of charging. Remember even the OE spec's are predicated on a 'FULLY' charged system.

You ask a question and an answer was supplied...the fact that you did not 'like' the answer is of no concern. The fact remains that to properly charge a system...the system MUST be changed by measuring the charge thur a weighted scale or other metering procedure....not a 'guess-ta-mation' of how much refrigerant was removed from a 12 oz can. or a 30 lb cyclinder
It is your vehicle...do with it as you determine best....but know that if this system is undercharged by a few ounces....the compressor will fail due to lack of lubricant migration. When this compressor fails, the repair can be quite extensive (think $$$$)....but once more it is your money.

Good luck!!!!

-------------------------
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 June 09, 2011 at 1:56 PM by iceman2555

NickD on Thu June 09, 2011 2:55 PM

Year: 2003
Make: Chrysler
Model: Town & Country
Engine Size: 3.3L
Refrigerant Type: R134a
Ambient Temp: 90
Pressure Low: 35
Pressure High: 110
Country of Origin: United States

Won't get into charging by pressures, but looking at what you have, your differential pressures are really low, and charging more is not going to solve your problem. Would expect to see around 28 psi at 90*F on the low side and around 230 psi on the high side. Adding more refrigerant will cause both sides to increase where you want your low side to go down and your high side to go up. It doesn't work that way.

Then you say your gauges are jumping, not a good sign either. So what happens to your pressures when you kill the compressor with the engine running, do they equalize very quickly? Like in a few seconds?

I suspect from what little I have read, you have compressor problems, mainly reed valve problems. Then would have to know the history of this vehicle. Because you tell me you are charging, interpret that as you have or had a leak. Did you even have zero pressures? If so, did you do a complete flush and replace the dryer adding the correct quantity of new oil?

I am suspecting sludge in your system, was stop leak ever added?

If you were to charge by weight, would still have the same problem.

NickD on Fri June 10, 2011 6:11 AM

Partially plugged orifice will also caused that symptom.

Dougflas on Fri June 10, 2011 7:33 AM

Another reason why chwrging by pressures is not a good idea is that depending upon the temperature of the vehicle will influence the low side pressure. Take a hot vehicle and measure the low side. Then cool the vehicle down. Restart the system and measure the low side again. You will have different pressures.

The experienced techs here will tell you the correct method to do things. If you don't want to follow them, it's your choice. Today's systems use less than 2 lbs of refrigerant. If you're off by 3 or four oz, that is a large perecntage of the correct charge. An experienced tech can fudge a charge; by your question, you're not experienced enough as yet to safely do that yet. Pull the charge and do it correctly. If you don't have the proper equipment, rent, borrow, or (I did not say steal!!) purchase the equipment.

rastoma on Sat June 11, 2011 8:52 AM

Ok, I appreciate what iceman was offering. I'm sorry if I was rough in my reply back.

The point I was trying to make, is this is a DIY forum. It may not say DIY forum. It may not have a heading that says 'fix all a/c problems yourself'. But this forum is just that. And I say that because look at the ones answering the questions. The company that put this forum up is doing so people can help people and then hope to sell product to the DIY'er.

This is not a pro's only forum. If it was, it would be restricted and the basic questions that get asked here 95% of the time all the experts know because the experts are the one answering the questions.

So I got a little miffed when I'm told (in so many words) that it can't be done by someone at home. And again, that's the majority of the people this forum and website (ackits.com) caters to... home shade tree mechanics.

Now..... after reading iceman's second reply, I understand what he is telling me and I can appreciate the offer of wanting to make sure the job is done correctly. I believe what you are saying.

But like most others here, I'm trying to do this myself, and I can't find a post yet where successful at home jobs were completed by weighing refrigerant. I checked at a Chrysler dealer yesterday where I went to buy an ambient air temp. sensor and asked them about weighing the refrigerant. The guy in service looked at me funny and said the gauges tell them when to stop, depending on the temperature in the service bay. The local Firestone service center doesn't weigh refrigerant. An independent garage with ASE and licensed a/c mechanics don't weigh refrigerant.

Now maybe if I were to say I found ONE place that doesn't weigh refrigerant then you could come back and say he doesn't know what he's doing. But 3 random, unrelated and NOT mom and pop grease pits, in 2 different towns, about 80 miles apart between the two farthest ones that don't weigh refrigerant, tells me that measuring pressures is acceptable.

To nickd - I don't think this compressor has an orifice, it has an expansion valve, which was replaced. I do have what I believe to be proper equipment. And I do have a digital scale that can weigh ounces, in case it's possible to use that in conjunction with 12oz cans. I can go and have the system evacuated and then pull vacuum again myself and measure the weight if you can tell me more information about that.

Other than that, some of the other problems I had I believe were coming from a fault set of manifold gauges. I had gotten a loaner set of Mastercool gauges from Autozone. I was having a terrible time getting refrigerant in the system and pressure levels were extremely erratic. Even with the engine and a/c off, the high and low pressure were extremely apart from each other.

I purchased my own set of gauges yesterday and without adding any more refrigerant, with the engine and a/c off, both high and low side were less than 5psi apart from each other.

So, can anything be done at this point without starting over?



Edited: Sat June 11, 2011 at 8:58 AM by rastoma

TRB on Sat June 11, 2011 1:46 PM

When a vehicle rolls down the assembly line. Is it charged by pressure or weight. End of discussion.

Why do these other companies not do it this way. Because it takes effort to do things correctly. Time is money. You think Firestone wants to pull out a reclaimer, remove refrigerant, pump down the vehicle and then recharge to the correct spec for their $19.99 A/C inspection?

Pressures supply valuable information. But if you don't know the refrigerant level! It's pointless to a degree. You are correct, AMA offers this forum to help others! "If" someone decides to support us great. Odds are most just use the free information that is provided. You also have gotten a response from a well know tech support for a very large company. He has forgotten more about auto a/c then most here will ever know. Would be wise to listen to what he is saying. Now if you don't have the equipment to follow his advice I understand. That's where it becomes a choice on your part as to how you want to repair the system. We won't provide info we don;t agree with. But will try to help with your questions. Good luck and keep the inquires coming.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

NickD on Sat June 11, 2011 5:55 PM

Quote
I purchased my own set of gauges yesterday and without adding any more refrigerant, with the engine and a/c off, both high and low side were less than 5psi apart from each other. So, can anything be done at this point without starting over?

Apparently, you still don't understand the difference between dynamic and static pressure, thought I already explained that Then you report using terrible gauges, not sure what kind of gauges you did buy, but for me, a 5 pound difference in gauge readings is an unacceptable error.

Could order a Mastercool AC basic training manual from TRB and read and study it. Wife twisted her knee last week, I looked at it, teased her about coming down to my work bench, but got serious and said you better see a doctor. Like to be a DIYer, but have to draw the line with some things.

Regarding your only specified pressures, already told you, you have major problems, and I have no idea what your did. But you are asking us, do you have to start over? Feel you know the answer to that.

rastoma on Mon June 13, 2011 6:39 AM

I really do not understand how the same questions that get asked by dozens if not hundreds of other people get answered without any kind of hostility, but I ask the same ones and get the 3rd degree.

I am NOT discounting ANYTHING ANYONE has told me. Just the opposite. I am using it all to learn. But when I ask questions elsewhere and get told different answers by a dealer that sells the car I own... different answers from a national service center (which no matter how little you like them, they are a huge company and must doing at least a few things right), you want to basically tell me I'm on my own.

And so I am taking in all this information. And not once have I said I don't care what anyone here says.

A large number of posts get made here with all caps, every other word misspelled, not a single period or comma per 100 words and people here understand the point they are making. I know I am an amateur/newbie/whatever you want to call it and acknowledge that. I have not in anyway said I know more than any one here. But apparently I don't explain myself correctly so whatever I say is interpreted as I am dismissing everything people HERE have told me. I guess I type TOO much information in the hopes of making sure I am making myself clear. But many of you just skim through my replies instead of reading every word and pick out keywords to use to make me look even more clueless than I already am.

All I have tried to say is, YES I BELIEVE YOU WHEN YOU SAY HOW THE PROPER WAY TO ADD REFRIGERANT IS DONE. But I prefer to do this myself and I know that people just like me have done very well in getting cold air to blow out of the vents of their cars and their a/c system has lasted for years afterwards. Some have not lasted so long because of cutting corners. I know that. So it's a crapshoot it seems. At first it was a price issue that I wanted to try and do this myself. Now I don't care about price, I thoroughly am enjoying learning about this a/c system in my cars with the help of everyone here. Also, since it's apparently true that measuring a system using pressure can result in a somewhat properly filled system, that's the road I would like to take. Just because I choose to do that doesn't mean I don't appreciate or believe everything else someone has said here. It just means I am at a point with this van that if I get 6 months to a year our of it, I think I will be lucky. I don't think I will have this same van a year from now so if I can use this as a learning experience for first time hands-on a/c work, then that's what I prefer to do because it's enjoyable and fun to me.

No I did not fully understand the difference between dynamic and static pressure initially when I started, but now I do. What I did not know is that I could have had a malfunctioning set of manifold gauges that I had loaned to me from Autozone. My reply stating I now have a 5 pound difference showing was to show I now should be able to get a handle on this because I am getting good measurements. Not that my numbers are good but the gauges are now working properly.

But it looks like I have already made a bad first impression and no matter what I say or do is going to have anyone looking favorable on helping me.

Edited: Mon June 13, 2011 at 6:50 AM by rastoma

NickD on Mon June 13, 2011 10:24 AM

Maybe what you need is someone to lead you by the hand, in person, can't do that on this board. I didn't have to comment, but when I saw YOUR posted pressures, you have problems that neither charging by pressures or weight will cure.

None of us are mind readers, but all of us, if we don't do it right the first time, have two choices, one is to do it again, second is to say, screw it. And all of us, even me, had a first time. I did a lot of study and reading before I worked on AC the first time. And also purchased the finest equipment. It worked the first time!

TRB on Mon June 13, 2011 11:12 AM

Let's approach this from a different direction. What did the car dealer and national service center. Inform you the pressures should be with a system 3/4 and fully charged?

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Bob on Mon June 13, 2011 11:56 AM

Do you have rear AC? The amount of R134a for front only 34 oz. If you have rear AC 46 oz.

JJM on Mon June 13, 2011 10:21 PM

I can make this easy:

Chrysler dealer = HACK
Firestone dealer = HACK
Independent garage = HACK

Service procedures from nearly every manufacturer calls for charging by weight, but I guess the hacks above know better than engineers who actually design and build the vehicles.

If measuring pressures alone is acceptable, then what happens when:

- The system is contaminated with air and/or moisture?
- There is a condenser and/or airflow issue?
- There is excessive oil in the system?
- The expansion valve is stuck open?
- STV or POA valve is malfuctioning?

In each of these cases, an undercharge would mask these symptoms and return "normal" pressure readings? Of course the system won't cool properly, so I guess their next step would be to just start replacing parts. And after all, why should they worry about replacing parts and needless repairs - it's not THEIR money (but yours you will soon be theirs).

Why bother with stickers and capacity listings then if not necessary? Going by the dealers logic of the gauges telling them when to stop, I guess we could add oil, transmission fluid, coolant, power steering and brake fluid in this matter, since actual levels don't matter. Yeah... just add enough oil to get that pressure reading up, and don't worry when the vehicle is running up or down hill and the oil is on the other end of the pan, the engine will be just fine without oil for a while!

Joe

When considering your next auto A/C purchase, please consider the site that supports you: www.ACKits.com

rastoma on Mon June 13, 2011 10:49 PM

I didn't ask them what the pressures would be as I was in each location for a different reason and just in passing mentioned that I was reading online how service centers generally filled R134a in cars.

The van has just front air only with rear vents.

Am I just asking the wrong thing here? I realize now that by asking what the pressures should be on a filled system, left out the fact that I had used 2 x 12oz cans of R134a. My main issue came with being told I need a scale, when for so many people filling with 12oz cans works and they don't have a scale.

So if the system holds 34oz of R134a and I put in 2 cans, do I count that I have 24 oz or is an oz or two include other ingredients (assuming it's only R134a in the can and not any additional oil, dye, etc.)? Then, while it's hard to guess what 90% of a can is, is there not a reasonable method to use that tells me when to stop adding the third can? If you tell me it can't be done, then tell me can I use a scale that measures ounces and pounds, by the use of 12oz cans, and know when I have the correct amount of refrigerant in the system?

I'm just not able to wrap my head around the fact that it's not possible for someone to do a reasonable job at home using 12oz cans of refrigerant from the parts store after seeing so many that do (along with a proper a/c manifold gauge and vacuum pump).

Ok, well thank you for the time you have all spent thus far in explaining this to me. It is appreciated and helpful.

TRB on Mon June 13, 2011 10:58 PM

First if you use a 12 ounce can. Always use one that has refrigerant only. You original question was not how many ounces did your vehicle take. I took it you were trying to charge by pressures. For a vehicle designed for a certain refrigerant. It's always wise to charge by weight, which has been mentioned over and over. Once you have the proper amount of refrigerant in the system Then pressures will provide the proper information on how the system is performing.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

JJM on Tue June 14, 2011 12:26 AM

Not ideal using cans, but you can use an inexpensive postage scale to weigh the charge in.

Just put the final can on the scale with the hose connected and measure the total weight - say it comes to 20oz for the full 12 oz can with the tare weight of the can and hose. (You must make sure the hose is stable so now to throw off the readings.) Now open the can tap and purge the hose. When done, say the weight is at 18 oz - you need 10 more ounces in the system (34 - 12 - 12 = 10), you'll so charge until the scale drops to 8 oz.

When charging with cans, you need to take into account losses when switching cans and purging the charging hose of air.

Joe

When considering your next auto A/C purchase, please consider the site that supports you: www.ACKits.com

NickD on Tue June 14, 2011 1:29 PM

Repost your pressures with your new gauges at 1,500 rpm, doors, open, AC on, blower at maximum and specify ambient temperatures and RH.

paulo57509 on Mon June 20, 2011 3:48 PM

Quote
Originally posted by: TRB
First if you use a 12 ounce can. Always use one that has refrigerant only. You original question was not how many ounces did your vehicle take. I took it you were trying to charge by pressures. For a vehicle designed for a certain refrigerant. It's always wise to charge by weight, which has been mentioned over and over. Once you have the proper amount of refrigerant in the system Then pressures will provide the proper information on how the system is performing.

I guess it's kind of like an automotive electrical system. Taking voltage and current readings with a half-charged battery yields meaningless data. A/C pressure readings are meaningless when they're taken with a under/over-charged system.

bromodragonfly on Mon June 20, 2011 6:02 PM

Systems that rely on an orifice, or a capillary, or a TXV without a liquid receiver are considered critically charged. The only real way to correctly add refrigerant in critically charged systems is by weight. Even if you're keen and calculate your subcooling after the condenser, and superheat after the evaporator - without a receiver, the conditions inside the system will vary with a rise or fall in load.

The problem with these 12oz cans is that they're tiny, and they don't weigh much. Some contain oil. Some contain dyes. They are difficult to weigh properly. It can be difficult to discharge their entire contents into the system. You have to use multiple cans and disconnect the hoses or regulator each time. Some people who do the DIY approach have very good results. Some have good results at first, and then performance will die off on a hotter day. Some screw it up completely and ruin a compressor or blow a line somewhere.

I would be very concerned if I went to an automotive shop and saw them charging cars with 12oz cans. But all of them will most likely use a 30lb cylinder and a charging scale, or a graduated charging cylinder for the specific refrigerant. The equipment is more expensive, but it's the only way to be sure, and it's a small price to pay for happy customers and little warranty work.

Anyway, I would take what the others have been saying to heart for now. Be meticulous in weighing those cans and accounting for any losses. Once you are sure you have the correct, or close to the correct charge, can you look at your pressures and temperatures meaningfully to see how well your system is performing.

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There is no knowledge that is not power