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changing from fixed orifice to TXV, possible?

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  • changing from fixed orifice to TXV, possible?

    I build a lot of "hybrid" type cars with different makes and model parts. Currently I am doing a popular swap of putting an old Ford truck body onto a 2007 Ford crown victoria police car chassis. The crown vic has a fixed orifice type system, and I wanted to keep it all other than the evaporator as the case is big and ugly. There are aftermarket evaporators available but all have a TXV valve.
    Is it possible to lose the crown vic evaporator and orifice tube and install the aftermarket evaporator and TXV valve?
    can I leave the accumulator on the low side or would I have to replumb and put a dryer on the condenser outlet?
    I assume the system has the usual high and low safety switches along with the clutch cycling switch, could I leave those in place?
    or should I just punt and see if I can remove the TXV valve from the aftermarket evaporator and put a fixed orifice somewhere in the condenser outlet line?

    I know this is not the normal type question but any help is much appreciated. I have the tools to make my own A/C lines so no problem making custom hoses.

  • #2
    Greeting to you too. Seems you just don't like the invasive HVAC boxes of either of the vehicles? If you want to play or are real serious about building a vehicle, both are chassis type for strength and A/C just invasive to your end "thing" that you are making why do you want A/C at all? Just asking as it gets in the way if style, appearance or other purpose is primary to this.

    Just thoughts on some IMO failed ideas of past. The Ford chassis once the choice for limousines sold new to cut body to essentially add a middle section for passengers a lot put the A/C works behind the driver's area seat/seats and just ran ducts to the rear rather than the guts of A/C stuff just insulate the ducts work well enough seemed OK but lousy IMO only with just those nobody would or could touch to make work for real a real limo company near me the vehicles didn't fit anywhere to work on had to outdoors and at location not many would even plain to look.

    It might help you to see what assorted coach builders already did that worked or not I'll let you look for which ones did engineer designs to modify for those ever important HVAC for basically locked in passengers separate from the creation that moved at all.

    In short would choose the priority probably can't have it all your way.

    Just noticed over some decades of vehicles I think failed at putting A/C last over other functions of the things.

    Corvette: Car made to go like a rocket, pack in HP like a nuke now want A/C? Fail! Too little room the heat invasion smoked parts for A/C so even small cabin area was just marginal knew and worked on the CCOT type ones some.

    VW Bus: Rear engine, air cooled now let's add A/C? Hmmmm? Compressor had to go on engine but no extra air back there so ran lines to front for condenser the length of them with sight glass under the things was a treat. FAIL. It was better than nothing but could neither heat or cool interiors very well but held lots of people if the objective.

    In real short think TXV will suit you best. You are creating this choose what's important first sacrifice what isn't as important something will be a trade off,

    MetroWest, Boston


    • #3
      Hi Tom,
      This is a 1960 F100 cab on a CV chassis with CV floor and firewall, so there is nothing as far as A/C from the 1960, and the CV HVAC case is not the best looking piece to be sticking out under the dash, but a retro looking 60s evaporator bolted to the bottom of the dash fits the style just fine. I have built many cars, I do one every year or so, but am new to retrofitting the A/C. Just did a "newer" car, 1981 trans am, and retrofitted 1995 Z28 A/C to the trans am with the 81 evaporator. It works great so now I want to start keeping A/C in my 1930s and up cars as well, this being the first to try an aftermarket evaporator.
      Am I on the right track as far as what needs to be done to lose the orifice tube and switch to the TXV? Keep the existing cycling switch, safety pressure switches, and can I leave the accumulator where it is on the low side or need to re-plumb and put a dryer on the high side before the TXV? It would be great to leave the accumulator where it is and only have to make a couple new lines to attach to the new evaporator.

      As I understand it the TXV take the place of the fixed orifice, being a more accurate variable control instead of the fixed one.
      Can you tell me why the difference in location of the accumulator vs dryer for the different designs?
      Last edited by rustystuff; 06-14-2019, 08:58 AM.


      • #4
        Wow, You are doing to VERY wild alterations and IDK what firewall of a 60 F100 looks like with nothing there if holes ready or what. I do recall this old not much had A/C OE it was nasty costly new plus think for trucks when they were just trucks would do the under-dash thing was ugly and invasive to interior was bad enough.

        TXV at least you are metering in the flow vs flood it and catch in an accumulator should avoid choking a compressor of choice with liquid. Best I can do it's so custom you already have more ideas of how to place things for what you want. Just try to shroud the condenser real well, tight to a capable fan even that of choice. If using a FORD engine see if you can find those flex fans they gave up on in the 70s for shooting blades thru the hoods about two did that and wasn't done any more but OMG they really worked great! An OE one not so sure of balance of the aftermarket ones I just glance not into altering that end up eating up water pumps or some PITA too much.

        Good luck. I can only be of so much help this is such a custom project clearly you have the ability to make up parts isn't so easy in MA anywhere the trade intensive work is about gone,
        MetroWest, Boston


        • #5
          Ok, This is going to get involved. I think it would be best to only re-use the Crown Vic compressor and build you own system around that. Orifice tube systems use different switches and setting than Tx valve systems. Also a Tx system needs a receiver tank on the high side to store liquid refrigerant ( and commonly holds the drier as well) and the OT system has the storage on the low side.
          The compressor and possibly the condenser can be re-used, but I would fit the largest parallel flow condenser (generic replacement type) as will fit.
          I would use a trinary switch on the high side for high and low cut out and for a condenser fan if used. The receiver needs to be placed between the condenser and Tx valve in the liquid line. I assume any evaporator will have its own "frost switch" to turn off the compressor to prevent iceing, If not, you need to either add a frost switch or an evaporator pressure regulator (expensive, but means the compressor will not have to cycle on and off, the EPR will control the temp). EPR's are called "two temp valves" in commercial refrigeration, and may be sourced from a commercial refrigeration supplier.
          Fit up your chosen evaporator package along with its Tx valve and eliminate the low side accumulator from the Crown Vic and run the low side line back to the suction port.
          If you are not using the Crown Vic controls, I'm not sure how the compressor load will act with the idle and WOT stuff for the fuel injection, as these are normally relayed to the engine ecm when A/C is called for, but I don't see it being a major problem.
          The Original Crown Vic pressure switches would give the wrong signals to turn off the compressor with the Tx, so I would run a new power feed to the A/C controls for the Evaporator, compressor clutch (thru the trinary switch) and basically make it independent of the engine controls.

          Once all this is done, and you have the system plumbed in, the hard part comes. How much refrigerant? Having built my own systems, and asked as many people as possible, I have never got an answer for a way to calculate the amount. You will need to go by trial and error until you find the correct amount. My advice, from experience, start by under-chargeing and work up in small amounts rather than too much. It will be a guess and you might have to make multiple adjustments before you find the best amount of charge. Good Luck!


          • #6
            Thanks cornbinder (I have 56 and 57 IH pickups as well!)
            Your thinking is what I figured, I would have to replumb for the dryer and add the trinary switch..basically rebuilding the system. I really want to leave the crown vic stuff alone, so maybe a better idea would be to remove the TXV valve from the aftermarket unit, install a orifice tube fitting and basically keep the original style system with a different evaporator. It looks like the TXV valve threads onto the back of the evaporator, so it should be easy enough to remove, but I dont know where the small capillary tube goes or if I would need to solder it closed or do something else with it.
            Here is a picture of the aftermarket unit and the TXV valve from the side and also a picture of an orifice tube fitting that maybe I could install in place of the TXV valve.

            Click image for larger version

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            Last edited by rustystuff; 06-14-2019, 09:21 PM.


            • #7
              If it were me, I'd stick with the Tx valve system, they are more forgiving of charge amount and mis-matched stuff.
              If you want to try the OT they make OT repair kits, that have the section of hard line that accepts the OT, you would need to splice it into hard line before the evaporator.
              If you do go the route of splicing in an OT PLEASE let us know how it works out, I for one, would be interested. My guess is, the orifice tube size will be critical and the size of the evaporator may play a part in what size, You are going into waters that I have not plumbed, so best of luck.
              I have done a few Tx systems and found it will work if you put the time in, So if the OT doesn't work out you can always go back and change the system around. Nothing ventured, noting gained.


              • #8
                Very true, no big deal if it doesnt work, I can always change it around. Charge amount will be the variable, but I will see if going by manifold pressures and vent temperature gives a decent result. I think I would start with the crown vic orifice, or see if I can find any info on orifice size vs evaporator size.


                • #9
                  DO NOT cut the small capillary tube from the Tx valve, it will destroy the valve. It should go to the outlet tube from the evaporator and sense the temp. If it has a separate small equalizing tube connected to the low side outlet, you will need to make a plug for that connection, but remove the tube intact so you don't ruin the Tx valve. From what I can see of your picture, the Tx valve just has a temp sensing line and not a equalizing line, so it should just un bolt.


                  • #10
                    ok, so just unscrew the TXV and tape it off out the way, but leave it connected?


                    • #11
                      In the future don't edit you older post with new question, they may not be noticed, just post the question by it self and we will see at as a new post on the thread.
                      The reason Tx valve system use the receiver on the high side and OT systems use an accumulator on the low side has to do with how excess refrigerant is stored when not needed for the temps.
                      Tx valve systems store the excess refrigerant as liquid in the receiver, so there is always liquid refrigerant available when the system is running. Depending on how cool the temps is, will determine how much refrigerant has to flow thru the Tx valve to just fill the evaporator with liquid such that it will all boil by the time it exits the evaporator. With low heat load, not as much is needed and the excess is stored in liquid form.
                      On OT systems the capacity of the system is varied by how long the compressor runs. The restriction is a fixed orifice but it still has to accommodate varying heat loads. The temp of the evaporator is controlled by the exiting pressure of the gas. Without an accumulator the compressor would cycle rapidly and burn out the clutch at heat loads below the rated capacity of the system. Since OT systems don't store any liquid refringent in the high side, the compressor runs less and takes less energy from the engine. The accumulator volume stabilizes the system, allowing long run and off period for the compressor at lower heat loads. Because there is little storage of excess refrigerant, and what little there is is stored as low pressure gas, the amount of refrigerant in a OT system is lower and more critical to get right when charging the system. This makes them much less forgiving of over or under charge than Tx valve systems.
                      Since liquid refrigerant expands in the order of 200 times when it turns to gas, the amount of excess capacity that can be stored in gas form is much less than can be stored in liquid form for the same volume.
                      If you tried to use a low side accumulator on a TX valve system with a low side pressure switch the compressor would cycle on and off before the Tx valve could really start metering refrigerant, in short the two system would fight each other. If you tried to use a high side receiver on an OT system, too much refrigerant would continue to flow into the evaporator once the compressor shut down, and without a buffer volume in the low side, the compressor would cycle rapidly and the evaporator would ice over.
                      In short the two system function very differently from each other. The Tx being more forgiving of mis-matched amounts and parts at the expense of energy used to run the system.
                      Last edited by Cornbinder89; 06-16-2019, 01:18 PM. Reason: 200% to 200 times. wrong wording


                      • #12
                        No, you can remove it completely, but the little tube is like a temp bulb for a mechanical temp gauge, it should be just held to the outside of the low pressure (exit) line, If you open the case, and remove any insulation, you should be able to remove it intact. Some, but not all, have a 2nd small line that is connected to the exit line. This will be either a male flare or male compression fitting, but I don't think I can see this equalizer line on your valve.


                        • #13
                          sorry about the edit, point taken, and thank you for the excellent information on the two system designs. Based on that I will try removing the TXV and using a fixed orifice, maybe I should try one for a smaller car like a honda that would have a smaller evaporator than the crown vic. I doubt these evaporators are that big.
                          Have you ever tried a variable orifice tube? Maybe the best thing to use on a Frankenstein system?

                          Click image for larger version

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                          • #14
                            I prefer Tx valve systems, and most of what I work on have that systems (heavy trucks). SO I have no experience to give on the variable orifice tube, but do try it an let us know how it works for you. As I said, you are going off into the unknown, so anything is possible.


                            • #15
                              Thanks for all the help and information, much appreciated! I will update on how it works out.