I have done automotive A/C for some time now but have started a business doing mobile work on heavy equipment. Approximately 70% of the time there is no tag showing the proper weight of refrigerant required. About 20% of those units have a sight glass which helps resolve the problem on those, to some extent. In some cases I am doing the work for a dealer who supplies me with the information. My problem is with about 30% of the units that I work on. I have been charging to a high side pressure of about 225 psi on a hot day and around 200 when it is a little milder. I know an over charge is going to show high pressures, there is a the possibility that some of these units may be under charged. Most of us know that an under charge will affect oil flow and can be very damaging to compressor. Here's my question, is there a better way to charge a system if you could not get the proper information on gauge readings or quantity of refrigerant specified by the manufacture? I have been told by someone in the past to keep adding a quarter pound at a time until the high side gauge spikes and then remove a quarter pound. The problem is I have never seen the high gauge spike unless the fan is not working. Any advice is much appreciated.
With our equipment, pressures at spec vary greatly. For example a Deere machine will usually run at much higher pressures than a Cat, just the way the system is designed I guess. Whatever machine we are working on I call the dealer if I don't have specs available. Cat is easiest, they have an A/C book that lists 90% of their models and what the amount of charge they take, including oil. The other mfg'ers are not that convienient.
Thanks but the local area Cat dealers are either to lazy to look this book up or are really having problems finding it. Could you provide a little info on the book.
The cat book number is SENR5664, All products air conditioning and heating R134a. Should be able to just give dealer book number.
a little trick they taught us in school (several years ago) vacunm down. then charge liquid thru high side till pressure equalizes. this will get you very close on charge. try it knowing what it holds for total charge
That's a cool trick. Another way I was shown was to check your vent temps and see if its good (40 F) and make sure the low pressure line at the compressor is as cool as a beer by touch. Again just another one you have to be careful with. 200psi sounds high to me but if it is working leave it alone. What machine are you working on? Maybe someone will have the correct specs and can help you out.
I will try that FSERVICE. I have never put liquid in the high side before. I would imagine it would be recommended to manually crank the compressor before starting the unit. Would this work for both expansion valves and orifice tubes? The other question I would have with this is that I would likely have to heat the tank on some units depending on the temperature. One of the challenges I had was on a piece of mining equipment that I worked on in the spring when it was cool out. There was no information listed for the refrigerant charge. I was working on the equipment in the cool weather and it was going down a couple thousand feet underground where to where it's hot. With that unit I put cardboard over the condenser to simulate a hot environment and charged it to 175 psi on the high side. Who knows where the vent temp would be in the hotter temperatures. It was only about 40 degrees outside at the time. I currently do work for the local Deere dealership so finding information for those is OK for now, until they start doing their own work. I have found with their units the high pressures are around 200 psi on average. That's based on about 5 different types of equipment that I have done for them.
That's the hard part of engine driven A/C work. With an electric unit you can charge it by the amperage draw on the compressor.
One thing I noticed about the few pieces of equipment whith A/C we have ( two trucks and a farm tractor) is they all hold around 4 lbs of refrigerant.If Im just adding refrigerant to the system I use a thermometer in the vent duct and when I see 50 degrees F I quit filling .
i might have not made myself clear on the LIQUID CHARGE thru the high side port!! first vacuum down system to at least 500 microns THEN charge LIQUID Freon thru the high side port. till the low side pressure gauge comes up & the Freon stops flowing. no need to heat the tank as you are using LIQUID NOT VAPOR!!!! DO NOT open the low side port while u are doing this as it will mess up the flow/amount of Freon that enters the system, as the liquid goes in thru the metering device (TXV or ORFICE TUBE) it flashes off becoming vapor on the low side of the system filling it with VAPOR NOT LIQUID.
To clarify, you're doing this with the system "not in operation", correct?
yes its NOT running... the compressor is NOT operating
I love it fservice. Next time I do one Im going to try it. Do you have any other tips for topping a system off without knowing how much is already in the system? I usually fill it until I see on the high side 150-175psi on a warm day here. I usually put my bottle on a scale and don't put more than a pound in depending on the size of the system for example I would feel comfortable putting in more in a loader as it takes five to eight pounds than an excavator that usually takes two pounds. And the fact with the loaders most of them are undercharged after they are worked on because certain people don't own a scale. I found this out a few times changing failed compressors but not leaking compressors as I scale it out and after I do work I vacuum test it with a micron gauge to confirm there are no other problems.
Andrew C, have you ever seen a book or list of AC charge weights for current Deere machines? Sure would be nice to find one seeing as most of the specs are wrong in Service Advisor
This is great guys, please keep the information coming. It is very much appreciated. I do use a micron gauge on about 50% of the units I work on but here is the problem. I do field service which is 1 to 3 hours away. I advise the customer that the system should be drawn down to 500 but in most cases they let me run the pump for 1/2 an hour. Obviously they don't want to pay me for standing around. I do recommend that when the unit is down for service etc.. to have it done properly. Whether I see it back or not time will tell. The other 50% of the calls are local and the unit is shut down for a period of time so it can be done properly. On these jobs I can let the pump run longer. I use my good equipment on these, Robinair 6 cfm dual stage pump and yellow jacket brute 2 gauges with a 3/8 vacuum line but it still takes a long time to reach 500 microns. For example I had a unit with a leaking fitting so I replaced the fitting and the receiver dryer. Checked for other leaks with nitrogen, everything was OK. The system had not worked for a few weeks so I let low pressure nitrogen flow from the high pressure side to the low side to help dry the system. It took 4 1/4 hours to get the system to 500 microns. Any advice on how to draw the system down faster. My next route was to remove the shredder valves to speed the process. The other issue is that I too have seen a lot of compressor failures, don't know why some of this is new equipment with a full charge. Here is how I handle this problem and please let me know any other recommendations. I change compressor obviously, replace receiver dryer and flush the line from the compressor to the condenser. That is as far as I go, I have tried in the past to flush the condenser but have never had any contamination come out. I think it would cost as much in flush agent to clean a condenser properly then the cost of a new one. I know that there are proper machines that would do it but who has that kind of money. Any other recommendations? FSERVICE great info. I am going to try that on a few different size systems. Thanks, Guys
cutting edge, as I said in a previous post I do work for the local Deere delership. Just yesterday I asked the parts salesman to look into it. I have ordered the Cat book and when it arrives he wanted to see it so he will have a better idea what to look for. I will let you know what becomes of it.
Cutting edge. I haven't found other weights other than the ones in service advisor. There are a few dtac cases about low charge from the factory but usually they were ag cases. The weights I have found are usually pretty accurate unless there is another problem in the system, they seem to work. There are a few cases that are good troubleshooting guides. Hittachi case 3 2011 0110. 69491. John deere fos book about ac gives some high specs dependent on temp 80 f 150-170 90 f 175-195 95 f 185-205 100 f 210-230 105 f 230-250 110 f 250-270 Low 1-30psi vent temps below 75 outside 20f vent 75-90 outside 25f vent above 90f outside 30f vent To me these vent temps seem too low. If it is between 30f-40f at the vents I would say there is nothing wrong with it unless it takes a while to get there.
Deere says genesolv 2004 (TY16134) works well. I have never used it though. They say you can flush it through 6-8 times before disposing of it.
One way to check it is to measure the temperature of the condenser outlet, and how much cooler it is than the pressure indicates...this is called "subcooling" and tells you how much extra liquid you have in the condenser. Once you start to see subcool you know the condenser is full and it should be solid liquid reaching the evap. inlet. However, it seems that no one method is fool proof, and on an unknown system I like to just pick a good hot day, run it and "titrate for effect" as they say in medecine...let a little more in at a time and monitor the effect until it is cooling right, then try to resist the temptation to add a little more.
Hey guys, keep in mind that if you have a low pressure going below 6 psi there is no oil movement. The minimum pressure no matter what system you have must stay above 6 psi. I have seen the pressure get low on a couple pieces of equipment but below 6 psi on the low side usually means an overcharge. Please correct me if I'm wrong. On a couple pieces of equipment the pressure stayed close to the minimum threshold but when rpm's were brought up it usually climbs. Feller bunchers for example usually run at max rpm. It all depends on the piece of equipment.
Birken Vogt, I know there is no actual answer to this question but could you elaborate on how sub cooling may help to charge a system or test to see if the system is fully charged. Obviously I have heard of sub cooling, don't completely understand it 100% but have a good knowledge of the principle. I know that it would help to diagnose problems on the high side but how do I determine the proper charge from that I don't understand. How do I know if the system is fully charged? Please expand further so some of us may understand this better. Thanks
I don't have the answer either but I will do my best. I don't think anybody really has a full grasp on its exact effect on the system, or if they do, they don't work for truck or equipment manufacturers because we all know that they continue to this day to turn out trucks and equipment that do not cool very well right out of the factory. It is frustrating. The answer you want is that the compressor compresses the refrigerant and discharges it to the top of condenser. The top rows of the condenser cool the hot gas down to the temperature where it starts to condense. (Condensing happens at a higher pressure when the temperature is higher, therefore the compressor is there to increase the temperature so that the refrigerant will condense at the elevated temperarures present.) There it begins to condense on the metal walls of the condenser as it works its way down. This is happening at a theoretically constant pressure and temperature, since, whether you have one pint or one gallon of liquid in the condenser at a given pressure, the temperature remains the same. It is just that more and more of the vapor is condensing to liquid as it works its way down, giving up heat as it goes, and that is what the fan and surface of the condenser is for. If the quantity of charge is sufficient, the last, bottom few rows of the condenser will be full of solid liquid. This is where subcooling comes in. This liquid is still at a somewhat elevated temperature and the last few turns are still giving up heat, so the temperature of this liquid begins to drop below the condensing temperature mentioned above before it exits the condenser rows. Measuring subcooling at the condenser outlet will give you some idea of how many rows of the condenser are full of liquid. This must be done very accurately with a probe made for the purpose and surrounded with an insulating compound. It would be even better to put multiple probes on the last few rows of the condenser to know where subcooling starts (the liquid level) but we are getting into engineering now instead of field service, and in real life it isn't that clear cut anyway. In the old days we used to use a glass window on the receiver/dryer and charge to solid liquid but some manufacturers say that with R134a, the window may never go solid anymore, and they are usually hard to see anyway. The bottom line answer is, who knows? Like anything, they make it work good enough to get it off the showroom floor, and patch it up good enough to make you go away, and after 1 year, it is up to you to try and keep it working.
None of my Cats is new enough to have cabs or AC but with this 105° heat we have been having it is good to have some of the cars or trucks AC working. My 89 Jetta diesel has a sight glass where the high side line exits the condenser. It was very easy to tell when it was charged. 00 Subaru is real finikey as to charge. Compressor will overheat and kick out. I have found if I keep rpm over 2000 and rolling down the highway it will keep going.
something to keep in mind is sub cooling ONLY works on TEV systems!!!!!
I have to admit fellas, I'm way out of my expertise with A/C systems, still a learning novice myself, but I've come to the conclusion that AC is an exact science that at times can still remain simple. All sorts of thermodynamic principles apply, but at the same time, as TD25C stated, stick a thermometer in the vent and when you see 50F, stop adding refrigerant, and as Birken Vogt added "resist the temptation to add more". I can attest to this, my 2008 Peterbilt, accumulator system with no sight glass, thought I'd add a little more R134A, had a negative effect, no longer making cold air, only cool. Released some of the pressure/refrigerant and cold air comes back. Hmm, there is an exact science to add refrigerant until it hits a certain level of cold air and resist to adding more. I'm intrigued by the concept of FSERVICE of doing the vac draw down, then adding liquid to the high side until pressure/flow is stabilized, then proceed with start up and finish refrigerant charge as needed, this would speed things up a bit, but I'm still in the learning phase, especially when it comes to troubleshooting problems with working systems. Very good knowledge at this thread.
If you had a CCOT system with no data, how would you go about determining charge level? If I understand correctly you would like the evaporator to be full of liquid. Do you want the suction accumulator to be full or empty, and how would you go about finding the level? I know you want to keep liquid out of the compressor like always. When I worked for the fire department we had E-350 cutaway chassis ambulances with a box module on the back, which had the stock orifice tube on the cab and a TXV on the back A/C. They worked great, both sides. It always struck me as funny but it worked.
Just adding a little info in to Birken's comment. I do work for the ambulance services here in Ontario and have for the last 18 years. Ford actually makes a ambulance package that has the a/c lines run to the bottom of the cutaway chassis just behind the drives seat. They have done this since 1994. The odd thing is that the cooling problem is usually a complaint in the front of the vehicle that is controlled by the orifice tube not the rear that is TXV controlled. When the system get's low, 90% of the time it is a complaint about the front A/C. Just wanted to through that out there, it’s a little off topic.
I have some HVAC experience under my belt. If you learn and understand exactly how Subcooling and Superheat works you can tackle any refrigeration problem with a fluke clamp on thermocouple and a set of gauges. Sent from my iPhone using Tapatalk
Forgot to add this link this is for R22 and R410A refrigerants I can't find the one for automotive systems http://www.hvacsalesandsupply.com/Linked Documents/Tech Tips/Proper System Charging.pdf Sent from my iPhone using Tapatalk
Sounds like Ill have to do a bit more reading. Blazin you said to use clamp on temp probes, will a temp gun work instead of buying probes, or is not not accurate enough?
I believe it is very important that you use probes made for the purpose, and that they be installed properly. It is kind of a fine, detailed measurement that you take. The page on fixed orifice vs txv applies to home/office a/c and not necessarily automotive. The principles are the same but the details on how and what the measurements are are different. For instance, the suction accumulator is used on car fixed orifice systems, but not on home/office systems. I think this is to prevent liquid slugging of the comressor under varying load and compressor speeds. How and where to measure superheat in this type of system is not clear to me. There is very little info out there on technician's theory of automotive a/c systems, mostly just "vacuum and charge per nameplate" which is, of course, only good if the nameplate can be read, and the system has not been piggybacked as in the ambulance, and the nameplate was correct in the first place (I have seen that too)
You should ALWAYS remove the Schrader valves when evacuating a system. This will speed up the process for you. Another thing you can do is to triple evacuate. To do that, let the vac pump run until you see the needle isn't moving much lower, then isolate the pump and let refrigerant flow into the system until you get about 1 or 2 pounds of pressure (just enough to get above 0) repeat this procedure two more times and try get the vacuum as low as you can without the customer going ballistic about you standing around. 500 microns is the goal but sometimes (like you said) you just don't have the time. Don't add too much refrigerant between vacuums or when you open the system to the pump, it will blow the oil out of the vac pump. Hope this helps.
Im a little confused, when I fill the system I evacuate and then check for leaks with the vacuum gauge and fill using the vacuum in the system. I cant understand why you would remove the shreader valves unless you re-vacuum after you evacuate.
u should know that it is a violation of the EPAs montreal protocol to vent Freon into the atmosphere!!!! that practice is very outdated & illegal!! just remove Schrader valves from system & use a good pump. tell the customer they get what they pay for!!!
there is a tool that allows the valve to be removed & installed while the system is under pressure/vaccumn!!
He is doing it that way to use a little refrigerant to displace any air that may be trapped in the system a little quicker than vacuuming it forever and waiting for the air to make its way to the pump. It would also work ok if you were to blow the lines out with refrigerant instead of vacuuming assuming the dryer was dry. But this isn't legal or cheap to do.
You are right........I should have said to use nitrogen and only bring it up to 0 psi.
The only tool that I have seen is for hvac applications not auto, could you point me in a direction to find it, thanks.
In field service of equipment A/C, our foreman won't allow for that much downtime of the machine, they would rather it run with the windows open. lol We recover and evacuate the system with the vacuum pump on it for no more than 15 minutes, then recharge.(this is just for minor repairs, not component replacements btw) The methods may not be perfect, but then again this is being done in the 'field', and it gets the machine up and running quickly with a happy operator. The shop jobs get more attention of course. Field servicing of heavy equipment is a touchy subject with most companies, downtime on the machine is critical as it costs more than the repair normally. Our field trucks use an air powered vacuum pump that runs off the compressed air system, we got them from Bumper to Bumper auto parts.
IF u cant make time to fix it right,( my thoughts are wait till you can) BUT then I open that can of worms!! So get a big CFM pump from a HVACR company itll pull down faster. will run on 110volts off genset/welder they are pricey but will make the boss happy that the equipment is up & running.. mine is made by JB & is 8CFM!!!
mine is made by FJC.. Ill try get the PN# for you when I find what the %$@$^# I done with my book!! I know its here someplace
Thanks fservice, I also own a jb, the 6 cfm version, half the price of the snap on ones and better quality if you ask me. I had one of those air powered ones but it wouldn't pull down past about 20 inches of mercury. Will make the system work but not as well as with a proper vacuum pump. I just checked snap ons website the have a version of that tool but they want too much money. $180. Ill see what fjc has.
Oh, that's happens to you as well eh?
I found their p/n 2750. It comes up with $140 on ebay. Does that sound about right?
Here are some good articles on automotive AC theory. http://www.imcool.com/articles/aircondition/index.html
I forgot to add when working A/C systems dont overlook other simple issues like the condenser & evaporator core's being stopped up with debris,loose fanbelt ,etc.Pretty common problem on farm & construction equipment thats working in the dirt. Also when I am charging up the farm tractor I run the engine at 1800 rpm to help on the air flow accross the condenser.on motor vehicals like cars & trucks it helps to put a large fan in front of the vehical to help the air flow as to simulate highway speed when charging a system.Without good air flow ya aint gettin any cool air.
yes especially here lately, since iv been so busy!! I don't think it has anything to do with getting older!!! lol
that's bout what I paid.. still haven't had time to find the catalog. it is worth every penny in the time it will save you over the season!!
The first thingH