• Login or Register Here.
  • Login is located in the upper right corner of all pages.

Announcement

Collapse
No announcement yet.

AC Charging problem

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • AC Charging problem

    Hi all, First post. I installed a hot rod air conditioner system in my 40 Ford PU about 9 years ago. This year I decided to finally charge it and get it operational. The shop that charged it said the pressures weren't right even though it was blowing pretty cold. A couple of weeks later, it stopped blowing cold. Suspecting a leak, I added some R134A with a small can and a low side gauge and it began to work again. I had a friend at a garage introduce some dye into the system and I located a small leak which I corrected by snugging up the connection. Unsure of the charge level. I took the truck back to the shop that initially evacuated and charged it. He evacuated and charged the system again, well at least he tried to.
    The low side of the system was going into a vacuum and the high side is about normal.
    He concluded there is a blockage, most likely the TXV. After he evacuated the system again, I ordered and installed a new TXV. No love...same issue. I noted that even though the system had been evacuated, there was pressure in the line between the receiver/dryer and the evaporator when I opened the system. I didn't think much of it at the time but after the new TXV didn't fix it, I decided to go back in and look at things. The shop recovered the refrigerant again.

    This time, when I opened the system, there was the same pressure at that connection. I removed the line completely. I tried to blow through it and I could, in one direction, the other way, it was blocked. I snaked out and cleaned the line and blew it out with compressed air and re-installed it. I pumped it down with a Robinair Venturi pump. (I have a 16CFM compressor to run it) It went to 30 inches and I held it there for about half an hour. I tried introducing refrigerant into the system, no dice. The low side was in a vacuum and the high side was about 100 lbs or so. Since it wouldn't take refrigerant, I shut it down and removed the TXV. I'm not a very experienced AC guy but the TXV was closed at room temperature. The old one was open at room temperature and it closed after about half an hour in the freezer. From this I concluded that the new TXV wasn't working correctly and I reinstalled the old one and pumped it down again.

    My charging procedure was: introduce the refrigerant through a manifold gauge set, relying on the pressure in the can and the vacuum in the system to get an initial amount of refrigerant into the system then start the engine and try to charge. Although I got some into it, I had to jumper the low pressure switch to get the compressor to run.

    The system was still going into a vacuum but less and less as it slowly took gas. I stopped after 1-1/2 cans (about 18 oz.) The system takes 28 oz. but the high side was about 250 psi. I think I may have needed to supplement the engine fan to keep the high side down.When I stopped charging, the low side was 10 lbs and the high side was close to 250.

    I know the system can't be overcharged with the amount of refrigerant that's in it but not sure if I should keep trying to charge it.

    Any Wisdom?

  • #2
    Hi Tom C and welcome: Nothing likes sitting unused A/C stuff or much for 9 years! It's just too long oil never moved around if a PAG would leak out some would say a normal something per year if ever known exactly right (?) ounces of oil and the 28oz of 134a.

    Whole vehicle is custom to just for laughs where did this kit put the compressor? Higher or low in this system? So far it's custom not easy to know precise expectations but you seem to have a problem with what equipment you are using. You almost can't have any vacuum on one side and nothing on the other plus you said 6CFM Venturi vacuum isn't used for A/C the CFM was how much air was used at what pressure the vacuum can't reach close to 30Hg, general seal level if exact is 29.92Hg just BTW.

    Dessicants wherever they are, are probably junk have finished absorbing moisture and PAG oils absorb moisture if exposed to air then turn acidic.

    Can't know but should be carefully checked out by a shop with tons of superior equipment for checking the system where blockage may be if any. I personally just can't know from here need some hands on checking person/tech should know it wasn't used for 9 years to help diagnose it out.

    *Vacuum pumps: You would need a real vacuum pump not those Venturi things not for this all air must be out and kept out mean no mistakes with that,

    Tom
    MetroWest, Boston

    Comment


    • #3
      I suspected things weren't going to be happy after 9 years. The system was closed the whole time. Once I did get it running, I wasn't happy with the sound of the compressor so I swapped in another same model Sanden that came from a working vehicle. I also installed a new receiver/dryer at that time so outside of the evaporator and condenser and hoses, the stuff is pretty recent.I hear you about vacuum pumps but 29" is 29" no matter what type of pump it's generated with. Besides, every time I take it back to the AC shop, it gets evacuated with a "real" vacuum pump. It's not having a difference on the condition. The compressor is mounted in the factory position, as the engine I used came from an AC equipped car.

      The whole AC kit came from a company called Rainbow Air in NC. Its identical to a Vintage air kit, as a matter of fact, the new TXV that I got from Rainbow air was a Vintage air part.

      Tom, I see you're in Metro West area, I'm right near Gillette Stadium in Foxboro. Do you know of any really good shops out your way?
      Last edited by Tom C; 08-25-2018, 10:01 PM.

      Comment


      • #4
        I'm in Marlborough. Family came from South St., Foxboro of course that goes back to 1895 (no typo!)
        A/C in MA is a b*tch. Have to put stuff away off season there's no room for all the stuff in your way MOST of the year. Dealers will also keep in mind when cold refrigerants don't flow and few or nobody keeps it in storage all year above say 70F somewhat like propane doesn't work well cold, spray paints machines or not.

        I asked location being a "Hot Rod" most would use a Chev. 350 (5.7) anything parts wise is made for that block. A low compressor floods with oil and chokes and high ones go dry each a problem the high up one sitting will be so dry if not purposely lubed it will self destruct over that many years at first engagement already zero lube throw debris all the odd stuff will happen in short order - usually?

        Venturi vacuum? That's flow of air over a tube essentially can't reach 30 Hg - never saw one get close maybe 18-20 real Hg. By rights that's enough to remove moisture but don't count on it. Would work for a little while or lots longer if R-12 tolerant of lots more than 134a inferior junk IMO in comparison. It's what we have avoid that 12a crap and run if you see 1234yf just light it on fire.

        OK: It sat is the trouble at hand. Moisture did invaded with temp swings as you know it's been switching heat waves, downright cold, soaking wet - all of it the dew you see on a window or metal is inside things too as droplets of water oil on top prevents it from evaporating - how special!

        Here's the trouble. Debris if already means system get trashed just a new or working compressor is good for a few minutes if that and start all over again! No forgiving either debris or moisture.

        It locked pressures! It really can't! Your gauges and the fitting are not working properly if the whole system was dead or not being used properly. Some 134a I call Acme quick connects use Schraders and some use (useless) ball valves - you see the ball just removing the cap. If in a vacuum you are sucking in air while vacuuming it just use low side you really don't need both IMO no it should charge or vacuum both.

        Air in lines of gauges needs to be purged out or vacuumed out.

        ? Who in your area does this all year? I really don't know and you are just 35 minutes away or so doesn't really matter just we live the same weather and insane costs of everything.

        Who? Not sure if still there I'll let you check was "Ray Everett" A/C anything, Westboro, MA near center rotary there. He can't still be working the place may be?

        Hey - 134a found cheap at "Tractor Supply" just $4.99 for 12oz cans all with new EPA tops that don't work as intended yet for me adaptors and all just leak out idea was they wouldn't.

        Lost - anyone long in biz stopped, moved or passed away in any order of that! Not a great "State/Commonwealth" for A/C anything. Look for ASE certified shops if for diagnosis only and for cost of 28 ounces should be nothing really as A/C goes may take an hour for a vac and charge then see what it does or doesn't do AGAIN. Once you lost info have to start there again a TXV set up should work with just two cans if you don't purge out much add the rest if it runs cool - use water on condenser to really suck last 4oz in,

        Tom
        MetroWest, Boston

        Comment


        • #5
          Before you say 29" is good enough look at this chart:

          Remember, just like any refrigerant ,water absorbs heat as it boils, 29" will just start the boiling at 80 deg. any cooling of the piping due to that boiling will stop the process.
          Add to that, conventional "compound" gauges are very inaccurate at measuring vacuum in my opinion, hard enough to discern 28 from 29 never the less 29 from 29.3"! I don't trust my gauges to 100% accurate in their readings, only that I can use them as a guide, the numbers should not be taken as absolute but rather they should read the same system to system.

          there are electronic vacuum gauges that can, but their price is out of reach for most of us, and aren't really necessary for most jobs.
          It is why it is recommended to shut off the vacuum and watch for a rise in pressure, a small rise indicates moisture boiling to gas, a large rise indicates a leak.
          A venturi vacuum pump may do an adequate job of removing non-condensables (air) from the system but not moisture. Even so my books recommend three sweep charges to get it all out.

          Comment


          • #6
            Great chart! OP and Cornbinder. I don't even own a Venturi vacuum thing never needed one for anything. There's just no way IMO only for lack of witnessing one do more than maybe 18-20 give or take. You can get that out of engine vacuum!

            Sorry if a repeat but air = moisture even in a dessert. That can cause quick frost right at X valve the game will show all erratic work then not at all.

            All info for detail charging must be observed all at the same time at the given temps, specific RPMs knowing adequate airflow as well plus really helps if not right have touchless IR thermos looking for where the functions of "change of state" go wrong if in the wrong spot or too severe. All that stuff can cost a freaking fortune plus see this all at once if it behaves again catch it right in the act.

            Try other gauges I frequently can't make a good connection or not at all with one brand and another will? No joy need doubles of everything!
            Tom
            MetroWest, Boston

            Comment


            • #7
              Also, Tx valves shouldn't open and close, they should vary a restriction but always pass some refrigerant. There are some that will close on a rising low side to prevent rapid heating of the condenser with the compressor off, but these are more likely used in commercial refrigeration and not in automotive.
              Think about it, if they did shut off then there would be no need for a "frost switch" and they would starve the compressor for returning oil. All go from passing a small amount to a larger amount of refrigerant but they don't "open" and pass unlimited amounts nor close and pass nothing, it is why we have different Tx valves with different tonnage ratings. Too large a Tx valve on a smaller system will have trouble regulating the amount needed for the smaller system and too small a valve on a larger system will not pass enough to fully utilize the full area of the evaporator
              Placing a Tx valve in a freezer is likely to get moisture in it as the air inside cools and the moisture 1st condenses then freezes. It isn't a good test of anything and shouldn't be done..
              To put it another way:
              the Tx valve's job is to measure the temp at the inlet and outlet of the evaporator and allow enough refrigerant through the valve that it is still boiling to liquid at the outlet (for 0 superheat) or if the superheat is set a few deg warmer (if the bulb is place on the line after the last set of fins) that the outlet is X deg above the inlet. No where does it state what the temp of the evaporator should be, just that the Tx is passing enough refrigerant to make use of the evaporator surface area.
              Last edited by Cornbinder89; 08-26-2018, 01:39 PM. Reason: workings of the Tx valve.

              Comment


              • #8
                Until you figure out what was plugging that line, all else is moot. anything that can plug a line will plug a Tx valve. Drier beads?

                Comment


                • #9
                  Originally posted by Cornbinder89 View Post
                  Until you figure out what was plugging that line, all else is moot. anything that can plug a line will plug a Tx valve. Drier beads?
                  Agreed, but the TXV wasn't plugged, the line to it was and since it was only plugged in one direction, I suspected a "flap" or some other piece of the inside of the hose was causing the problem. Actually, I was disappointed not to find anything recognizable inside that hose, no sludge, residue, drier beads (the dryer is new anyway).

                  Please let me know if I'm understanding this correctly... The compressor was pulling down into a vacuum on the low side. I took this to mean that something was restricted enough to keep the flow of refrigerant back to the compressor from happening. So, in order for the low side to operate at 25-30 lbs of PRESSURE, there has to be more refrigerant available to the suction side of the compressor than it is able to take in, hence the positive pressure rather than the suction.

                  When the system was apart, I flowed dried compressed air through the hose from the discharge side of the compressor, through the condenser and through the hose that was attached to the input side of the receiver/dryer. I has no obvious restriction to flow in either direction. From what I can tell the next test should be to discharge the system, remove the TXV and test the evaporator alone to see if it is restricted. If the restriction is present, this would help explain the fact that the system never had normal operating pressures from the first time it was charged. Currently, it is charged by weight to 28 OZ of R134A, the low side pressure is at 10 lbs, the high side is at 240 lbs ad the outlet air temp is about 35F. My concern in operating it this way is that these readings are at an elevated idle speed approx. 1100 RPM. I'm guessing that having such low pressure on the low side would only get worse as engine speed increases, starving the compressor for oil.

                  If you can comment on these thoughts, it would be very helpful.

                  Comment


                  • #10
                    Quote from prior post "> Currently, it is charged by weight to 28 OZ of R134A, the low side pressure is at 10 lbs, the high side is at 240 lbs ad the outlet air temp is about 35F. My concern in operating it this way is that these readings are at an elevated idle speed approx. 1100 RPM. <"

                    Just that for the moment. Is this to say you know it has correct 28oz and vent temp is 35F just sitting still not anything else? If I saw only that would call that working as well as possibly intended if not a bit too cold to output temps could frost up evaporator.

                    Maybe just me or reading into this all wrong? Sorry if so not intended. I don't believe your measurements of much of anything would want other of same equipment to prove these observations. L=10, H=250 and can blow 35F if quiet and stayed working you probably wouldn't be looking for troubles at all.

                    The key note is it's an add on, aftermarket A/C set up for a HOT ROD no real telling from the maker what creation it's really going to be used in - all of which would be painstakingly well engineered if a production something to make zillions of.

                    Just notes and refresh: The Venturi effect: (Google it, it's a person's name for that bit of physics) It isn't that perfect said I've never seen it used for A/C work effectively?

                    "Dried compressed air:" Sure - that's so you don't get water in the tank for the compressor as much or water in air tools not dry totally just better or lasts longer before you drain water from a compressor's tank sure would use that for tools or blowing things out - anything you use compressed air for.

                    I wouldn't expect some normal pressures in the middle of some known standards for this just acceptable in a range and probably substandard performance if it worked it's best vs a production vehicle unless known to be lousy. Just a couple of many - never could make a 60s-70s Corvette freeze you out nor an air cooled VW bus. All wrong placement of parts it wasn't intended to be a rolling ice box.

                    Note on hose blockage: Hose intended for flexing in use A/C, brakes, hydraulics can fail inside making a Reed valve effect usually from use, age, trauma or bad luck.

                    Oil and compressors: If starved for any reason would fail usually make noise first not always for long (minutes) and would be all over. Apparently not? It's making pressure if those observations are even part close?



                    Tom
                    MetroWest, Boston

                    Comment


                    • #11
                      Originally posted by Tom C View Post

                      Agreed, but the TXV wasn't plugged, the line to it was and since it was only plugged in one direction, I suspected a "flap" or some other piece of the inside of the hose was causing the problem. Actually, I was disappointed not to find anything recognizable inside that hose, no sludge, residue, drier beads (the dryer is new anyway).

                      Please let me know if I'm understanding this correctly... The compressor was pulling down into a vacuum on the low side. I took this to mean that something was restricted enough to keep the flow of refrigerant back to the compressor from happening. So, in order for the low side to operate at 25-30 lbs of PRESSURE, there has to be more refrigerant available to the suction side of the compressor than it is able to take in, hence the positive pressure rather than the suction.

                      When the system was apart, I flowed dried compressed air through the hose from the discharge side of the compressor, through the condenser and through the hose that was attached to the input side of the receiver/dryer. I has no obvious restriction to flow in either direction. From what I can tell the next test should be to discharge the system, remove the TXV and test the evaporator alone to see if it is restricted. If the restriction is present, this would help explain the fact that the system never had normal operating pressures from the first time it was charged. Currently, it is charged by weight to 28 OZ of R134A, the low side pressure is at 10 lbs, the high side is at 240 lbs ad the outlet air temp is about 35F. My concern in operating it this way is that these readings are at an elevated idle speed approx. 1100 RPM. I'm guessing that having such low pressure on the low side would only get worse as engine speed increases, starving the compressor for oil.

                      If you can comment on these thoughts, it would be very helpful.
                      Systems can operated at lower pressures, even into less than atmospheric, many commercial systems do, so that doesn't worry me too much. As long as there is flow, it will carry the oil back to the compressor.
                      1 st question is where is the low side tap? If it is near the compressor or on the compressor it self, the low reading may just be the line loss and if the tap was closer to the evaporator it would read closer to what you expect to see. Does it raise up to around 30 at idle?
                      The 240 Psi High side indicates a condensing temp of around 140 degs, What is the temp of the air passing thru the condenser? You may have air flow problem across the condenser. A quick test is to mist the condenser with a water hose while watching the pressures and temps.
                      If I knew nothing, I would think you were slightly low on charge, but that would only be a guess and is not held out by the fact you charged to the spec'd amount by weight.
                      Your 35 deg outlet temp says things are pretty good. If you can get to the evaporator inlet and outlet pipes, you want them to be about equal. the inlet (after the Tx valve) and the outlet just after the fins of the evaporator, if they are even in temp, that says that there is enough refrigerant to fully make use of the surface area of the evaporator.
                      Don't fixate on just pressure readings, look at everything as a whole unit and if it is cooling well and seams to work, then don't worry about it.
                      With something that isn't factory designed, the installer has to be sure that there is good airflow over the condenser, and there is good heat transfer from the refrigerant to the air passing through the condenser.

                      Comment


                      • #12
                        Thanks for your comments. The low side tap is on the hose fitting at the compressor, so yes, it's as far from the evaporator as it can be but the line is only 20 inches or so long. The low side pressure is 10 lbs at idle. These tests were conducted in small garage on a hot day so available air flow was minimal however I did have a box fan blowing on the condenser but it was just probably blowing hot air around. I can certainly mist the condenser out in the driveway to see what happens to the high side. I also have a non contact IR thermometer gun so I can measure the inlet and outlet temperatures of the evaporator. Another thing I haven't done yet is to re-insulate the TXV and the bulb area on the outlet tube of the evaporator. It's quite possible that if the insulation was installed the evaporator temperature may be a little higher. If I understand correctly how the TXV works, it should be throttling the flow of refrigerant through the evaporator in order to maintain an evaporator above freezing.

                        Comment


                        • #13
                          OK - Better understood for me now. Not optimal setting for pressure testing and airflow boxed in a small garage NOT best. More, take pressures at raised idle not just idle IDK what pulleys would be on this for how fast compressor turns another spot to change results. The Tx does meter in liquid with the aim of it totally evaporating just in time so can send just the right amount of liquid/condensed gas which is why temps of last inlet and outlet are so close or should be. If bulb isn't insulated or in the right spot all bets off that you need to tend to.

                          Products to seal it or a putty that absolutely works hot and cold, wet and compatible for the job. Of course it catches heat send more, too much or just all wrong doesn't send correct amount on.

                          The water use can exceed what airflow can do if the right set up and can do that where it is or if possible do it outside, level is best and allow some run time in a ride around the block type thing for performance tests and pressures - it did for a bit it's just not optimal conditions YET. Keep at it. Doubt IRs myself unless they can prove themselves with another something known my own (two) don't like air rather something solid. IDK and don't ask I'm in a kitchen right now and ice cubes read about -10F about where I want them. Said don't ask why I have the thing in my kitchen!
                          Tom
                          MetroWest, Boston

                          Comment


                          • #14
                            Originally posted by Tom C View Post
                            . If I understand correctly how the TXV works, it should be throttling the flow of refrigerant through the evaporator in order to maintain an evaporator above freezing.
                            NO! the Tx valves job is to meter the refrigerant such that it all boils to gas by the time it reaches the outlet of the evaporator, regardless of temp. Basically, it looks at the temp of the refrigerant just after the valve, when it just boils out of the Tx valve, and compares it to the line temp at the outlet of the Evaporator. If both are about equal, it is metering the correct amount, if the outlet if colder it has let through too much, and if it is warmer, it needs to let more through. All of this is predicated on having the right amount of refrigerant in the system.
                            The frost switch, POA, STV, EPR are all ways to control evaporator temperature and are used in addition to a Tx valve. They do different things.

                            Comment


                            • #15
                              Thank you for the clarification. I will be sure to check the temperatures at the inlet and outlet of the evaporator coil.

                              Comment

                              Working...
                              X