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Faulty Expansion Valve?

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  • Faulty Expansion Valve?

    I'm hoping that someone can help me diagnose what appears to be a faulty expansion valve in a 1990 Volvo 240.
    The car was converted over to r-134a about 8 years ago and worked great until it developed a hole in the condenser. I replaced the condenser as well as the drier and vacuumed the system down for an hour and then verified that it held vacuum for a couple of hours. I added the recommended 2.2 lbs. of r-134a and got the gauge readings in the photo.
    The inlet line to the expansion valve is getting frosty while the outlet of the evaporator is staying at near-ambient temperatures. It was 90° in the shop today.
    From everything that I've read, it sounds like the expansion valve isn't allowing refrigerant to enter the evaporator at the correct rate.

    Any advice would be appreciated.

    Thanks very much.

    Last edited by Wren; 06-04-2019, 12:02 PM.

  • #2
    To be clear: you are saying the INLET to the Tx valve is frosty? The Outlet to the evaporator can get frosty, but the inlet is on the high pressure liquid side of the valve, and if it is frosty, then you have a restriction before the Tx valve.
    Pressures alone look undercharged, but that is only a guess, as pressure doesn't equal charge amount. Are you adding by weight (with a scale)?


    • #3
      Too low or a problem just by high pressure should be 2.5 X air temp coming in the grille +/- RPMs count, fans on and IMO inside a closed area who knows what air you are getting and where it's going? In thru, down and out under.

      Just my observations with retrofits done now was a rush long ago now that 80% of a 46oz system was guide actually no more than that. New condenser is probably not tube and fin so you have to wing it with all readings all at once. Stop, drive it around and see then if better or worse always watching how much went in. By rights you put too much in but that smacks of too low by quite a bit or lost a lot while charging just didn't notice or leaking at higher pressure but not what you see now?

      Car should have a sight glass isn't accurate for 134a but is a clue of just what's right there.

      If a guess it's way undercharge if that was a sudden loss with hole in condenser also chance you lost oil but would leave a mess.

      Unsure why depends on how fast is lost charge with the hole?

      First thought is way undercharged but there's so much to check while operating. You can tell a real blockage the temp along line changes for no great reason if you are sure BEFORE X valve it just isn't right of course that's why you are here!
      MetroWest, Boston


      • #4
        Actually, it's the txv itself that's getting frosty. The nut is where the valve joins the evaporator. Please see photo.

        Yes, in fact, the new condenser is a 16x21 parallel-flow model.

        I charged by weight using a 30# cylinder and am certain that 2.2 lbs. went into the system.

        Click image for larger version  Name:	Y3xP1-VCNylkakiX1etdbPHe4U_-xsSCgAIgYRuuM3lq-kEkVB6Ti_BDBoQ67Wu_X300NtExpk1pC_EC1bStJVO-4x-HY0pDCCYfYpcglo2_4ZO1RKDP4dq8YIKxiCRFDRWOn_iyVCciqeAXmWtZ16XJisFMetLEqfzCsPcejO6-hMWmWJiwEhhDtTfz2RRu_bsmcLcuHCqnMBgYqvDtoCV9XqVB0ahW-qFSVgJvWMlAxExVWEFMV0zwhV-GmCk Views:	0 Size:	96.9 KB ID:	1790
        Last edited by Wren; 06-04-2019, 07:52 PM.


        • #5
          I just can't see how it can be a Tx valve problem (with the charge amount correct) with temps you are reporting and the high side that low. With the low side near vacuum, all the refrigerant would have to be in liquid form in the receiver, and the pressure required to achieve that would be higher.
          Both low, high and low side is usually a sign of an undercharged system. Your high side condensing temp is around 104 and you say the ambient temp is 90! A liquid cooled condenser would struggle to do that, it is out of the range of what an air cooled could achieve.
          Either the "recommended" weight of charge is wrong, or the compressor is turning to slow. At what RPM were those readings taken? Are you sure there is no belt or clutch slippage? Still if slippage, I would expect a higher low side.
          If you want a low tech roll of the dice, keep adding refrigerant a few oz at a time and record the pressures. If both the low and high side start to rise you are making progress. Allow the system to "settle" between adds (let the pressures stabilize) and keep the RPM between 1000 and 1500
          Frost on the outlet of the Tx is normal, as the liquid refrigerant flashes to gas in the low pressure beyond the valve.
          When you shut the system off, how long does it take for the high and low sides to reach the same value? They don't have to totally read the same, but how long for the high side to drop to close to ambient temp and the low side to come within 10 deg of that?


          • #6
            Thanks, Cornbinder. I'll check the belt. Those readings were taken at idle, which is around 800 RPM.
            I'll make note of how long it takes for the pressures to more-or-less settle between adds tomorrow.
            I know it isn't the most useful tool, but here is the equalized-overnight pressures today when I got back to it. Ambient temperature was about 92°.
            I did notice today when I was taking the photos that the system is blowing cooler-than-ambient air, so now I'm wondering if the correct charge with the newly-fitted parallel-flow condenser requires a significantly higher amount of refrigerant to function properly.
            What do most folks do while wading through this no-man's land?

            Click image for larger version

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            • #7
              ">> What do most folks do while wading through this no-man's land?<<"

              Pull out a lot of hair to answer that question! New parts on an R-12 system usually use less than the OE but unless it's stated in with packaging who knows?

              Just a question on the overnight equalization readings shown - That's not equal in the picture. 92 + 100 show? That's a lot off. I don't think the system can do that but the gauges could be off? Do those come apart to adjust for accuracy?* Of course if they did would need some known accurate measure to set them to. More hair loss.

              *If they do some incredible highly accurate ones may have a screw in the back I don't see one on the face. IDK if in question and I am set to zero when not on anything and hope they can read equal just from your 30# bottle whatever pressure it has.

              Tweaking a system is plain hard and takes time also need to know there are no other faults with it or all bets off. Said somewhere most require a test drive around the block type thing get oils to settle where they will helps prove you've found the right spot. Write the amount down under the hood it known so it can be duplicated if needed later by you or another is just handy,

              MetroWest, Boston


              • #8
                If at 1200-1500 rpm the high side goes dramatically higher and the low side goes lower, I'd change the Tx valve. if the high side stays approximately where it is, I'd add more refrigerant. If you have a way to save what you put it, and the Tx is a bear to get too, I'd add refrigerant 1st.
                Parallel flow condensers don't generally add volume to the system, they add surface area, so as a rule you don't need to adjust the amount for them. The tubes are smaller and narrower but there are more paths to take.


                • #9
                  Totally agree and probably just to that Tx valve.

                  Sorry if a repeat but love this tool for A/C and in general.

                  The cheap type IN-OUT WIRED THERMOMETER usually a thing you'd put wired end out a window and base on a window sill thing.
                  Turns out at least ones by ACU*RITE are fast to instant! Placing the wired end in a center vent and run wired base to in front of the vehicle in sight you get both at a glance know what's happening live data.

                  They may make these thing just as tools for A/C I wouldn't pay it. These are about $10 bucks. Yes you can place the wire thru a closed door just think where. So simple they'll make the things illegal someday!
                  MetroWest, Boston


                  • #10
                    So I check the pressures while increasing engine RPM's and the high side didn't increase. Based on the advice above, I added 4 ounces of refrigerant and saw an increase with each addition.

                    Starting pressures at idle:
                    Adding 4 oz. refrigerant: -5/125
                    4 oz. more: -3/135
                    4 oz. more: -1/150
                    4 oz. more: 0/175

                    While the pressures seem to be going in the right direction, my vent temps are at ambient. Unless there's a stuck heater valve, I'm not sure what to guess could be the issue. I don't believe the heater valve is the issue as when I drove it over to the shop, I didn't notice any heat coming out of the vents. 240's are known to have heater valve issues and when one stays open there's no mistaking it. The heaters will keep you warm in sub-zero conditions, so it's pretty hard to not notice if it's on.

                    The inlet to the evaporator is still cold/frosty, but the outlet of the evaporator is at ambient temp.


                    • #11
                      Your high side is going up but not the low side, so I would change the Tx. The higher high side is showing that the compressor is stuffing the refrigerant into the receiver, but it can't get through to the low side. That points directly to the Tx as the problem. What threw me off the scent was the low high side pressure.


                      • #12
                        Thanks very much. I'll see about fitting a new tx and report back.

                        Speaking of which, I've heard that all newly-manufactured expansion valves should be calibrated for r-134a, but I've also heard otherwise. The one in the car has a r-134a sticker on it and we believe may have been installed at the dealer when the car was initially converted years ago. Any idea on what is being supplied today?

                        Click image for larger version

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                        • #13
                          A Tx valve only needs to be the correct size (in tonnage) for the system. It DOESN'T set or regulate the evaporator temp. it job is to meter refrigerant such that the inlet and outlet of the evaporator are about the same. In otherwords that enough liquid refrigerant is in the evaporator to make it to the outlet but not enough to pass liquid beyond the outlet. It does that regardless if the evaporator temp is 80 deg or -15.
                          It does its job by comparing the pressure on the inlet side of the evaporator (outlet of the Tx) to the temp sensed by the bulb. They are usually biased so that the outlet is slightly warmer, this is referred to as the "superheat" setting and on industrial valves is adjustable, but most automotive one are not.
                          Some also use a pressure connection on the outlet of the evaporator, to sense the pressure leaving the evaporator. This is called an equalizing line.
                          On a properly charged system pressure is directly related to temperature, so even that the temp is measured in different ways, they can be compared.
                          A Tx valve doesn't ever close fully or open fully it is a modulated restriction. If the outlet of the evaporator is way warmer then the inlet, the Tx open more to allow more liquid to pass, if it is close to the same or cooler it closes to limit the amount. It never cares what the actual temp is, only that the outlet is slightly warmer than the inlet.
                          If the Tx could or did regulate evaporator temp, we wouldn't need frost switches of cycling switches.
                          Since R134a and R12 have close to the same properties (otherwise we couldn't retro-fit) the Tx valve will work just fine with one or the other.


                          • #14
                            Thanks very much. I'll order a new expansion valve and report back after I've opened the system to inspect the line from the drier to the tx.


                            • #15
                              I pulled out the expansion valve expecting to see some sort of blockage (decomposed desiccant, etc) but it was clean. I was able to blow through the line going back to the drier and it was clear as well as blowing through the evaporator going back to the compressor, so it would seem that the issue is the expansion valve is faulty.
                              I tried to blow air through the expansion valve itself, but couldn't get any to go through, of course not knowing if I should be able to do so. I put everything back together, vacuumed the system down, and am awaiting the new Tx which arrives Tuesday.