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  1. #1
    1000+ Posts gerrypro's Avatar
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    Default Question for air con experts!

    Hi there all of you aircon experts. Here is my question.
    When the air con is not running ie. it is at rest, is the TX valve default position open, or closed?

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    Cheers Gerry

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    1000+ Posts robmac's Avatar
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    Quote Originally Posted by gerrypro View Post
    Hi there all of you aircon experts. Here is my question.
    When the air con is not running ie. it is at rest, is the TX valve default position open, or closed?
    With compressor not running and hi side and low pressure equalized ie the same.

    The bellows controlled by the thermal sensing capillary, will continue to operate, so while the coil of the evaporator remains "cold" there is a chance the tx valve may remain closed.

    However when evaporator temperature reaches ambient the tx valve will be open.

    This fact becomes self evident if you consider the function of the tx valve , as a thermally controlled refrigerant metering device with the flow sensing capillary sensing the evaporator outlet temperature.

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    1000+ Posts gerrypro's Avatar
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    OK then, this means that if the valve is a ambient temperature on a typical Aussie autumn day of say 16 degrees C. then the valve will be open! Correct?
    Cheers Gerry

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    1000+ Posts robmac's Avatar
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    "Open" may be an exaggeration.

    The tx valve is a metering device. So if the sensing bulb is at a temperature, that in operation valve settings would allow refrigerant flow
    some flow should be allowed.

    A tx valve is not an on/off device, it is metering device, controlled by temperature feedback from the outlet side of the evaporator.

    At ambient temperature you should have some flow through the valve. How much will depend on the what refrigerant the valve is designed for and the super heat settings.

    They are not too expensive, if in doubt replace it.

  5. #5
    1000+ Posts gerrypro's Avatar
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    Yes Rob I gather that the principle is that the flow is variable according to the sensed temperature of the evaporator outlet flow of gas. I am trying to avoid dismantling the entire heater box. I can see the TX valve through the side access panel. However the pipe work it is attached to is quite flexible and I run the risk of distorting them by trying to undo the large nut that holds the TX in place. As it is a CX access is rather limited without major disassembly.
    Can I also assume that if I can chill the sensor capillary tube then the TX valve should close proving that it is operational?
    Cheers Gerry

  6. #6
    1000+ Posts robmac's Avatar
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    Why not simply charge up the system and do a real test with the aircon running ?

    Gauge settings will soon tell if the tx valve is working.

    Tx blocked closed the evaporator will be "starved" of refrigerant. Conversely the evaporator will "flooded" if it's jammed open.

    Aircon systems are best serviced a working system.

    Trying to diagnose faults on a component basis isn't really practical.

    However I would check the tx sensing bulb is in intimate contact with the evap outlet pipe and the whole deal insulated with pressite (cork) tape.

    https://www.ebay.com.au/itm/Black-Co...-/122658942584

    External heat loads can play havoc with Tx operation.

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    1000+ Posts gerrypro's Avatar
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    Bulb is well contacted with the discharge pipe. It may not be the accepted norm to run a test on components of an open system but if I can at least establish whether or not the valve opens and closes it gives me an idea of my chance of success before I fork out for another canister of Hychill. I am also going to have new hoses made up and thus far I have removed them to take them to a place that can reproduce some new ones. As the system is open at the moment it is hardly practical to recharge.
    I have ascertained that there is flow through the valve at ambient temp. I will try to check for flow with the capillary bulb chilled. And see whether or not I need to dismantle everything ----I hope not! Many thanks for your input. I will keep the forum posted as to how I go!
    Cheers Gerry

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    1000+ Posts robmac's Avatar
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    How do you propose to cool the sensing bulb ?
    Being attached to the outlet of the evaporator there is considerable thermal mass in involved.

    And how will you ascertain the temperature at which the TX should open and close and if it's flowing refrigerant ?

    Regardless, I wish you all the best in both performing the task and interpreting the results.

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    1000+ Posts gerrypro's Avatar
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    I was going to spray some LPG over it, and avoid any source of ignition, whilst trying to blow through a rubber tube attached to the high side of the valve. Wish me luck!
    Cheers Gerry

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    Thankfully we use H valves in current models.

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    1000+ Posts robmac's Avatar
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    Quote Originally Posted by seasink View Post
    Thankfully we use H valves in current models.
    Electronically controlled Tx valve ?

    or Block style tx valve?

    I've never heard of an "H" valve.

    Please educate me.

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    An old name for the box valve. Turn one on its side and the drillings form an H. I think Ford invented them. Modern Cits have one mounted on the inside of the bulkhead where the lines enter from the engine bay. There is no bulb, and the diaphragm closes one end.

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    1000+ Posts robmac's Avatar
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    Quote Originally Posted by seasink View Post
    An old name for the box valve. Turn one on its side and the drillings form an H. I think Ford invented them. Modern Cits have one mounted on the bulkhead where the lines enter from the engine bay. There is no bulb, and the diaphragm closes one end.
    Called a block valve in the industry and nothing ground breakingly new, the fact that both evaporator supply and discharge ports pass through the block avoids the need for the external capillary in some (but not all) block Tx valves.

    The same technology is employed in both the old style and block valves the only difference is the implementation.

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    Quote Originally Posted by gerrypro View Post
    I was going to spray some LPG over it, and avoid any source of ignition, whilst trying to blow through a rubber tube attached to the high side of the valve. Wish me luck!
    Well that didn't work! Cannot get it cold enough! Looks like I will have to dismantle everything (**&^%$$()
    Cheers Gerry

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    1000+ Posts robmac's Avatar
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    Quote Originally Posted by gerrypro View Post
    Well that didn't work! Cannot get it cold enough! Looks like I will have to dismantle everything (**&^%$$()
    Why not just leave it as is and test when get the aircon up and running ?

    From my experience you have a better than even chance of the Tx being OK.

    The only thing lost will be a few hundred 100 grams of Hychill. If and when repair is necessary.

    IMO it is better to confirm a fault, and fix it.

    Rather than going looking for a possible fault . Expending a lot of time and major disassembly doing so.

  16. #16
    1000+ Posts gerrypro's Avatar
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    Good suggestion. I had the system open to replace a leaking hose on the H side to the condenser, after which I attempted to charge the system. It would not accept a full charge no matter what I did, and I still have a cannister approx. half full of Hychill. This despite vaccing the system down and holding 29 inches of depression for over 3 hours. I then wondered whether the TX was blocked as I had unusual gauge readings. I also suspected the Sanden 508 which is still relatively new but later tests running the unit gasless and the pressure switch by-passed showed that the low side was sucking properly and the high side was blowing. This would mean that the valves in the head are working properly and the unit is OK.
    I will try to recharge with the remaining gas and see what happens tomorrow!
    BTW What is your opinion of Hychill? The fellow that made my replacement hose said it was little better than BBQ gas with a few anti corrosion additives! ( but then he deals in R134a)
    Last edited by gerrypro; 21st May 2019 at 07:02 PM.
    Cheers Gerry

  17. #17
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by gerrypro View Post
    Good suggestion. I had the system open to replace a leaking hose on the H side to the condenser, after which I attempted to charge the system. It would not accept a full charge no matter what I did, and I still have a cannister approx. half full of Hychill. This despite vaccing the system down and holding 29 inches of depression for over 3 hours. I then wondered whether the TX was blocked as I had unusual gauge readings. I also suspected the Sanden 508 which is still relatively new but later tests running the unit gasless and the pressure switch by-passed showed that the low side was sucking properly and the high side was blowing. This would mean that the valves in the head are working properly and the unit is OK.
    I will try to recharge with the remaining gas and see what happens tomorrow!
    BTW What is your opinion of Hychill? The fellow that made my replacement hose said it was little better than BBQ gas with a few anti corrosion additives! ( but then he deals in R134a)
    Personally I won't use Hychill (or LPG) because both are extremely flammable. And I've been in the middle a a hychill fire during recharging.

    However I leave people to make their mind up whether they are happy with the risk.. Cue for double chevron.

    There is no doubt that Hychill is functionally a very good refrigerant which a low high side pressure.

    If you doubt my safety concerns, watch the video below. Dr Ian Maclaine Cross is Hychill's safety expert.

    It's worth watching the video right through: https://www.youtube.com/watch?v=k0K1WPCWm2k

    I will concede his "test" is moronic but the consequences demonstrate my concerns.

  18. #18
    Tadpole ozVTR's Avatar
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    [QUOTE=robmac;1614229]I've been in the middle a a hychill fire during recharging.
    QUOTE]

    How did you (or whom ever) manage to ignite the Hychill?

    Was this an automotive or non-automotive application?

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    The purpose of the Tx valve is to throttle the liquid refrigerant into the evaporator so that the evaporator is not flooded with liquid coolant, which, being incompressible, might be ingested by the compressor, leading to a compressor stall (or failure). In my experience, Tx valves typically fail closed.

    The operation of a Tx valve is fairly simple. The pressure from the sensing bulb (which is sensitive to temperature) works to open the valve. This force is counteracted by pressure in the evaporator (called the equalizer pressure) plus a spring which both work to close the valve. The weak point in the system is the sensing bulb. When the sensing bulb fails, the spring closes the valve completely. When this happens, the low side pressure will then be VERY low and the high side pressure VERY high, with no cooling effect.
    Cheers,
    John T.

    54 11BL; 61DS19 LHM (son's); 71DS21 BVH; 73SM 3.0; 73SM 2.7EFI; 73SM 3.0 (other son's); 74 Maserati Merak

  20. #20
    1000+ Posts gerrypro's Avatar
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    [QUOTE=robmac;1614229]Personally I won't use Hychill (or LPG) because both are extremely flammable. And I've been in the middle a a hychill fire during recharging.

    However I leave people to make their mind up whether they are happy with the risk.. Cue for double chevron.

    There is no doubt that Hychill is functionally a very good refrigerant which a low high side pressure.

    If you doubt my safety concerns, watch the video below. Dr Ian Maclaine Cross is Hychill's safety expert.

    It's worth watching the video right through: https://www.youtube.com/watch?v=k0K1WPCWm2k

    Point Taken!!!!!!! Thanks to the "LATE ?" Ian Maclaine Cross! Stupid to be in the car and strike a match!!!!!!!

    I will have it charged with R 134a.
    Thanks John for your explanation of the most likely failure point of a TXV being the capillary tube/bulb. Mine is open at room temperature so I assume it is OK
    Last edited by gerrypro; 22nd May 2019 at 09:25 AM.
    Cheers Gerry

  21. #21
    1000+ Posts robmac's Avatar
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    If the system was designed for Refrigerant 12 And you charge with R134a, the system will very likely be under condensed. ie have a very high head pressure.

    There are a few options to solve this problem.

    1) Fit a bigger condenser coil

    2) Add a second condenser in series with the first

    3) Increase airflow over the original condenser. Ie fit a couple of 300mm radiator cooling fans.

    Option one is usually best try to increase the surface area by 33-50 percent.

    Option two is often more practical, the second condenser can be installed horizontally.

    Option three is often much a compromise and loads up the alternator as well.


    The test will be the hi side pressure, if it's too high it loads up the compressor and reduces system performance. R134A has a very high head pressure to start with so it can be battle to keep it to a sensible level.

    And don't forget to fully flush the system (shellite driven by compressed air is a practical solution and more environmentally friendly than using R11,trichlorofluoromethane ) , change all O rings and use PAG oil in the compressor if you change to R134a
    Last edited by robmac; 22nd May 2019 at 09:59 AM.

  22. #22
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    In double chevron's apparent absence, I will go on record that I personally am a big fan of HC12 because of the superior thermodynamic properties and its superior compatibility with all refrigeration lubricants. HC12 (Hychill, Envirosafe, etc.) are mixtures of propane and isobutane. It is not the least bit surprising they would explode if exposed to an open flame. (The same thing would happen if you held a match over the petrol tank filler.) The main problem with HC12 is the danger to an A/C mechanic who is not warned that the system contains hydrocarbon refrigerant and uses a flame leak detector thinking he/she is looking for an R12 leak. In the larger scheme of things, 12 ounces of hydrocarbon refrigerant are probably no more dangerous than a petrol tank that is half full. Use appropriate caution.
    Cheers,
    John T.

    54 11BL; 61DS19 LHM (son's); 71DS21 BVH; 73SM 3.0; 73SM 2.7EFI; 73SM 3.0 (other son's); 74 Maserati Merak

  23. #23
    1000+ Posts robmac's Avatar
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    [QUOTE=ozVTR;1614271]
    Quote Originally Posted by robmac View Post
    I've been in the middle a a hychill fire during recharging.
    QUOTE]

    How did you (or whom ever) manage to ignite the Hychill?

    Was this an automotive or non-automotive application?
    Very much automotive.

    It was whilst working on a 505, removing the high side charging hose and had spontaneous ignition caused by what I think was a ignition system electrical discharge.

    Unfortunately I was wearing synthetic overalls, which started to burn and stuck to my arm.

    I could have been unlucky and could have worn flame retardant clothing however I didn't and suffered the consequences as a result.

    After that I made the informed choice to avoid highly flammable refrigerants.

    I don't consider myself a novice: I've been working with aircooled domestic and small commercial systems for 15 years plus. And with auto systems for a lot longer.

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    1000+ Posts gerrypro's Avatar
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    I appreciate the wisdom of your input Rob. If an incident could happen to you with all of your experience it might very well happen to a novice such as myself! Thank You!
    Cheers Gerry

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    1000+ Posts robmac's Avatar
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    Thanks for wrap up Gerry,

    However the reason for going in the "Gorey" details was not to give a warning.

    I was simply answering a question put by ozVTR.

    I'm no expert. I'm an amateur with a genuine interest , applying my knowledge from other disciplines exactly the same as many other AF members.

    And the school of hard knocks is a good way to learn.

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