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  • Honda CRV TXV system has be stumped

    Hi, I created this account specifically to try and get some insight into the issue I am having on a 99 crv. This is the first AC system I have worked on, but I am quite adept at car mechanics. Being in Vermont, and being the type of guy that drives old junkers, I never bothered with working AC, until my wife got pregnant. She would like working AC.

    I just bought the car, and do not know the AC history. AC did not work, but had some refrigerant in the system. I bought gauges, and a vacuum pump and charged up the system. The compressor ran, but I did not get any cooling. The low side pressures were decent at idle, but the compressor would pull into a vacuum if the revs were increased.

    I thought that maybe the TXV was sticking shut ( I only had a low side gauge at this time).

    I replace the TXV and the dryer. I vacuumed the system for a few hours. Added oil and dye and the specified weight of charge. That static pressures made sense, and I got cooling.

    Most of this work has happened with ambients in the 50-60 range, so its tough to really test cooling. I thought it was fixed.

    This weekend I took it on a long highway trip, and ambients got up near 80F.

    The compressor would cycle on, I'd hear some hissing from the TXV, and get some cool air and the compressor would kick off and air temp started climbing. This repeated every minute or so, and the system really isnt able to keep up with the heat load.

    I got home and threw some gauges on it, but it was back down to about 55 ambient. The charges still look the same, no apparent leaks.

    At idle, the low side may be around 20-30psi, high side is 80-100. If I increase rpm, the low side drops down to near zero while the high side climbs to maybe 120. Again, this is 55F. I do not know what the pressures looked like at higher temps outside.

    It seems like the compressor drops out when the low side drops below a setpoint after a certain amount of time, maybe 2-5 seconds.

    Now I think this sounds like classic low charge, but I put in exactly the right amount by weight, and my static pressures are dead on with the corresponding ambient. I added a hair more r134 in desperation, but there was no effect.

    The compressor shaft turns very easily by hand, and I feel basically no resistance.

    I am at the point where I think I will replace the compressor, but the low side dropping down to near zero has my confounded. (with the old TXV it dropped right into the negative, but the charge may have also been low at that time).

    To me, my high sides seem consistently low, and I would expect the low side to be around normal if I had a weak/worn compressor. What I cannot figure out is how I could have a low side that drops with RPM while the high side creeps up some. Is this the TXV closing down almost shut because the refrigerant flowrate is too slow because of a weak compressor? That doesn't quite feel right to me.

    Another thing I cannot figure out is: does this car normally cycle the compressor, or would the compressor run and the txv take car of matching the load? I think my cycling on the interstate is because of the low side being sucked down too far and the low pressure safety switch opening.

    The condenser fans work great, new cabin air filter, the rest of the HVAC system works great and all the flaps are in nice shape.

    The compressor has 217k miles on it.

    I am about ready to order a new Denso unit, because I don't know what else to try.

    Thanks for reading all that.

  • #2
    I think you have a refrigeration leak, and it's now low. I recommend having a shop check for leaks, and to pull out and weigh the amount of refrigerant in the system, the only real way.

    Static pressures don't tell a whole lot. Typical high side pressures at about 2000 rpm are 240 to 280 psi.

    Comment


    • #3
      I do not think I have a leak. It holds vacuum overnight with the vacuum pump off. The static pressures are the same as they were when I added the exact right amount of r134a by weight, and correspond exactly with the temperature scale on the gauges (as they did two weeks ago when I charged it). The system has never worked right, even right after I charged it with the exact correct amount of r134 by weight.

      Comment


      • #4
        Not a simple problem! I would NOT throw parts at it, better to damage old parts than brand new ones.
        1st question is where is the high side tap located in the system? If it is after the condenser, then you might be looking at a clogged condenser. If the system has a high pressure cut-out located closer to the compressor than the high side tap, this would explain the system shutting down, then cycling back on. In otherwords, you are not "seeing" the true high side pressure. I agree that all pressures seam low, but if you are sure you have the right amount of refrigerant in the system, then look for other causes, don't add more.
        Start by feeling the temp of the compressor outlet line, if it is too hot to touch, then move down stream until you find a rapid temp drop in the line or condenser, this will be close to the restriction.
        Other than the condenser, the receiver is another possibility, but I believe you already changed that. Look for a crimped line, or anything where there is a large change in temp before the high side tap.
        Tx valves don't "close or open" all the way, they are a variable restriction but always pass some refrigerant.
        The hissing sound, is likely low pressure vapor passing thru the Tx instead of liquid.
        If possible try and get a manual on the car in question, it would be helpful to know what kind (at the set point) of any switches or sensors.
        A 1999 is more likely to have switches over sensors, but I am not an expert on them.

        Comment


        • #5
          Thank you for the response. I don't have the car in front of me, but to answer some of your questions:

          -I believe the system has only switches. There is what is termed a "dual switch" that threads into the receiver/dryer. I believe there is also an evap temperature switch as well.

          -I dont think the compressor outlet line has ever really felt hot. I think the outlet lines have been warm and the suction lines have been cool. But not cold or hot.

          -The high side tap is right in the tube that connects into the dryer, so the reading there should be the same as the "dual switch" is seeing. However, I'm not sure which side of the condensor this line connects to. I will need to investigate on the actual car. I believe the receiver/dryer, dual switch and high side connection port are all downstream of the condenser, so it stands to reason that the condenser could be plugged and that could cause the symptoms that I'm seeing. I dont know how common that would be, or why that would be. The old TXV I took out was very clean inside, so I do not suspect a fouled up system inside.

          In the attached diagram, you can see #18 is the high side port, and #17 is the dual switch.
          https://www.hondapartsonline.net/aut...ses-pipes-scat

          -I will look more closely for kinks and maybe take a video of the gauges with the RPM's varied.

          -Is there anything to be said about the fact that I can spin the compressor shaft very easily with one finger? I really cant even feel the resistance of a piston compressing anything even with the system charged.
          Last edited by vtpsd; 05-28-2019, 04:26 PM.

          Comment


          • #6
            It could be a compressor, but I find it odd that it will pull to vacuum if the compressor is shot, one would think if it was loosing pressure by the rings, it couldn't pull a vacuum on the low side at the same time. The compressor "crankcase" is the low side, so one would think leaky rings would make the low side higher not lower.
            The dryer is always on the liquid side of the condenser, as part of its job is to store liquid refrigerant.
            I can turn my A-6 when properly charged, if I try to turn it fast, I feel some resistance, but it doesn't take much to turn slow. It is a judgment call, and hard to say from this far away.
            If the outlet line from the compressor stays cool, and the pressure stay low, even on a warm (80 deg) day, then I would be more inclined to think it is a compressor failure. Bad reed valves or one or more stuck open could be the cause, but better to rule out everything else before condemning the compressor.
            Alternatively, you can evacuate the system, put you thumb over the outlet port of the compressor and see if it will build pressure against your thumb when you spin the shaft. I just hate to see you spend money on a compressor to find out that wasn't it.

            Comment


            • #7
              I totally agree, how could the compressor pull a vacuum if it was worn, and that was the only problem. I don’t know how common the condenser plugging really is or how that might have happened. I think I am going to replace condenser and compressor for a total cost of about $275. The idler bearing is bad on the compressor as well.

              Comment


              • #8
                Just add some: To do even just that bearing I'm pretty sure compressor has to come out no room thru a wheel well last was metal there not a plastic shield. If the case and doing it check oil remaining for junk/debris. That would change the approach.

                BTW, do keep in mind holding a vacuum is possible and still have a leak. The math of it, the full vacuum at sea level is holding OUT just 14.7 PSI. System just with a small charge can be lots more or working 100s. Other all my own do this if left out in super cold? Took me a long time to guess that but shafts to seal doesn't expand and and contract well or the same as warmer, oil evidence not found and it's sealed later. Been same for many of my own of course should know the best.

                Just finished one (doesn't matter) vehicles are 1989 and 1997 model built in '96. So after pulling hair out for years with same vehicles just defeat them from working off season at least it saves the compressor which would run with defrost or defog request or just engine heat enough to fool them pressure is enough to work at all for a short time.

                So back to top - if doing compressor you would see debris by all odds if low and think it was once would do it,

                Tom
                MetroWest, Boston

                Comment


                • #9
                  Your money your choice, I am one who HATES throwing parts at something, but sometimes that is the best you can do. It would be interesting if when you get the old compressor out, if you put your thumb over the outlet and spun the shaft to see how much pressure it would make.
                  One thing about shaft seals, unlike most other applications, the shaft seal on an A/C compressor sees the highest pressure when it is stationary, but we expect it to seal from vacuum to several hundred PSI,
                  Some Hyd pump seals see high pressure but only when the pump is in operation, many others have drains behind the seal so they don't have to hold back a lot of pressure. A/C shaft seals are the only ones that see the highest and lowest pressure when the shaft is stationary, it is surprising the do as well as they do.
                  Older seals are of the "face seal" type where the sealing surface does not ride on the shaft, the two halves are secured to the case and shaft, the shaft half rotates with the shaft, and the case half is stationary in the case. Some of the newer compressors have a lip seal that rides on the shaft, and while this may seal slightly better when everything is new, WILL wear a groove in the shaft over time that even a replacement seal can not fix. With the old face seal tech, all wearing surfaces get replace when the seal is changed, and they use the compressor oil to do the sealing, kind of like a vacuum pump.
                  If the outlet pipe from the compressor isn't hot hot, and the pressure is low, then a bad reed valve might be it and a replacement compressor is in order. A reed valve failure isn't likely to put debris in the system, but if the condenser has some age on it, I would change it as well, NEw England winters are not kind to them.

                  Comment


                  • #10
                    That was so well said Cornbinder! 1st the "Parts Cannon" as I've said here and there. NO. Each one you risk a new failed part vs the original becomes the problem!
                    Hope this pic shows it's a joke in a way about that...…..That isn't funny!
                    >

                    The magic of sealing a rotary shaft from leaking under vacuum or pressure, liquid or gas at temp extremes below zero to way above boiling then expect it to last is just beyond realistic. Past and some present ideas were to make a metered leak whatever it is such that item get dirty with use. That oily dirt in turn protects it. If it stays totally dry the conditions outside end up corroding it. Can't win - chose a way and live with it. Duplicating it later if excessive has the failure rate isn't a surprise,
                    Tom
                    MetroWest, Boston

                    Comment


                    • #11
                      I completely understand that throwing parts at a problem isn't ideal. But what other methods of diagnostics can I do at this point? I DO need to replace the idler bearing, which I have had mixed results with in the past. A denso compressor is $195. The condenser is about $60. My condenser appears to be in good shape from the outside. The car has never been in the road salt.

                      My wife is pregnant with a baby due in August, and I am in the middle of building a house, and sometimes you have to do the best in the situation that you are in. Evacuating the system repeated times just to rule out one item at a time is not really an option for me. Its kind of a hail Mary type situation, since I have other very important things to attend to.

                      I do not feel great that a new compressor will fix the problem. The fact that the system can go into vacuum while at the same time having a low high side pressure just does not feel right to me.

                      I took a couple videos the other night to show the action of the gauges. Since this is my first time using AC tools, I was hoping someone more experienced could take a look and see if something jumps out that I am missing. The two things that seem the strangest to me are :1) the high side pressure seems to react slowly and 2) The low side can get pulled into vacuum in certain circumstances.

                      You can see in one video, I did find evidence of a slow leak at the outlet of the condenser. I can also see some potential UV dye around the compressor shaft, but its very dirty down there and very hard to see without taking the car apart.

                      https://www.youtube.com/watch?v=m4YnSi2bpUM

                      https://www.youtube.com/watch?v=iU8HP2-1xrQ

                      Comment


                      • #12
                        I watched your videos. Yes, the condenser fitting is leaking, both oil and refrigerant. Your pressures at high rpm look low, but not terribly bad. If my vehicle, I would add another 1/2 can R134a and see what happens, and then decide whether to add the remainder. $4.88 at Walmart.

                        Yes, that's a gamble, but for me would be worth the gamble. But you also said the compressor idler bearing is bad too, and that needs to be addressed too ! Or it will bite you in the butt someday, maybe soon. The addition of more R134a is just to learn, maybe the information for R134a amount for your Honda is wrong, like someone installed a larger condenser in the past.
                        Last edited by Cusser; 05-30-2019, 09:38 AM.

                        Comment


                        • #13
                          Originally posted by Cusser View Post
                          I watched your videos. Yes, the condenser fitting is leaking, both oil and refrigerant. Your pressures at high rpm look low, but not terribly bad. If my vehicle, I would add another 1/2 can R134a and see what happens, and then decide whether to add the remainder. $4.88 at Walmart.

                          Yes, that's a gamble, but for me would be worth the gamble. But you also said the compressor idler bearing is bad too, and that needs to be addressed too ! Or it will bite you in the butt someday, maybe soon. The addition of more R134a is just to learn, maybe the information for R134a amount for your Honda is wrong, like someone installed a larger condenser in the past.
                          Thank you for reviewing the videos. Do you think it seems like the high side reacts a bit slow? Does the vacuum seem strange to you?

                          If you look at my first post, you can see that I did add more 134 just to see if I might have undercharged it. No difference in performance, other than my static pressures now indicate I am slightly overcharged.

                          The idler bearing will be addressed with the new compressor. Like I said, I have replaced those in the past with limited success, but dont want to mess with it this time.

                          Again, thank you for all the responses. I have learned quite a lot about AC systems with this experience so far. I hope I can get it figured out in the end.
                          Last edited by vtpsd; 05-30-2019, 09:47 AM.

                          Comment


                          • #14
                            I had a couple other thoughts.

                            1) When I replaced the TXV, the sensing bulb came with new insulation. I had some trouble getting the insulation nice and sealed. Is it possible that a poor insulation job has caused the sensing bulb to pick up some of the warmer air surrounding it? Its my understanding that this might open the TXV more than it should.

                            2) It looks like the only thing that can cycle the compressor on this system is the dual switch in the dryer and the evaporator temperature sensor. I believe the dual switch kills the system when the high side drops to something very low (like 25 psi) and also kills the system when the high side gets to something very high (like 450 psi). I do not think I have ever had either of those conditions.

                            I wonder if the evap temp sensor could be reading incorrectly and tripping off the compressor too early? That doesn't really explain the hissing TXV. Also, I have never gotten vent temps in the 30's; best i have seen is maybe 42 before the compressor and fans kick off. I dont think the evaporator switch is supposed to kick off until the coil is in danger of freezing.

                            Comment


                            • #15
                              Of course bulb has to be in the right place AND properly insulated or nothing is going to work right.
                              Ask for the stuff locally to seal that up. I use another product totally not going there now.
                              Cut out for high side should be way less than 450 is just way too hot and some things would burst up there.

                              The aim for general best outputs, center vent should be about 42F maybe some see 40 but not intended to stay in the high 30s. Double check your way of checking - hate that always making sure things are accurate with another something.

                              Reason is ice of course first. Just try it in most vehicles put panel vents on only and NO A/C at all while moving along too at good speed, say 30MPH or more. Look at (set this up) real outside air coming at the vehicle and what you see at that vent even windows open. In almost anything I've checked gains 5F thru the ducts the engine heat just isn't blocked out that well plus a heater core many flow all the time seal those off too if violated for some reason.

                              In short the aim is output of about 42 IMO? If you've ever had a constant flow of cold at you anywhere just in one spot it really gets annoying rather better volumes of 42 air to do it still should just fine or car just leaks too much other reasons,
                              Tom
                              MetroWest, Boston

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