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Thread: TXV Stuck Open?

  1. #1
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    TXV Stuck Open?

    Just replaced compressor in a Federal open deli case. R404a, receiver, TXV, sight glass, no pump down, no other valves. Pretty basic system. Evacuated to 150 microns, weigh in charge. Start up. All sound great, but liquid line is hot to the touch and suction line and compressor dome are very cold. No gauges hooked up at this point.

    I figured, it just started up, it’ll settle in. Started putting my gear back in the van, and when I cam back in, the unit was off on high pressure cut out. Condenser is perfectly clean, and fan is running the right direction and moving good air. Gauge up and find high side pressure around 380. Sub cooling is 35 and superheat is almost zero.

    Remove about 1 or 2 lbs of refrigerant and get high side down to 310 (120F) and superheat goes up to 30.

    On a system with a TXV and receiver, adding or removing a pound or two of refrigerant should not have this much effect. Right? I’m thinking that I might have a TXV that is stuck open. In 35 years, I don’t think I’ve ever seen a valve fail open. I see them fail closed quite often.

    Any thoughts?
    If God didn't want us to eat animals... He wouldn't have made them out of MEAT.

  2. #2
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    Quote Originally Posted by GenesisRefrig View Post
    Just replaced compressor in a Federal open deli case. R404a, receiver, TXV, sight glass, no pump down, no other valves. Pretty basic system. Evacuated to 150 microns, weigh in charge. Start up. All sound great, but liquid line is hot to the touch and suction line and compressor dome are very cold. No gauges hooked up at this point.

    I figured, it just started up, it’ll settle in. Started putting my gear back in the van, and when I cam back in, the unit was off on high pressure cut out. Condenser is perfectly clean, and fan is running the right direction and moving good air. Gauge up and find high side pressure around 380. Sub cooling is 35 and superheat is almost zero.

    Remove about 1 or 2 lbs of refrigerant and get high side down to 310 (120F) and superheat goes up to 30.

    On a system with a TXV and receiver, adding or removing a pound or two of refrigerant should not have this much effect. Right? I’m thinking that I might have a TXV that is stuck open. In 35 years, I don’t think I’ve ever seen a valve fail open. I see them fail closed quite often.

    Any thoughts?
    Someone pull the dime trick on the power element?

    It’s a known “emergency repair” for a bad power element to get the valve to open, take power element off, put a dime in it and reinstall until next business day. Sometimes get forgotten.


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  3. #3
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    Forget the dime thing that will not work. Replace the valve and be done with it.

    Sent from my SM-T387AA using Tapatalk

  4. #4
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    Quote Originally Posted by rickl View Post
    Forget the dime thing that will not work. Replace the valve and be done with it.

    Sent from my SM-T387AA using Tapatalk
    I was suggesting that it’s possible it WAS done possibly because that particular person didn’t have a power element on his truck at the time and forgot about it, this causing the valve to be wide open and noticeable now that it has a new compressor.


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  5. #5
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    OK cool. Your right on that. I never done the dime thing. We carried the sporlan tex kits on the truck.

    Sent from my SM-T387AA using Tapatalk

  6. #6
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    Thread Starter
    I’m planning on going back, and replacing the valve, then putting a full charge in on Monday. Right now we’ve got a partial charge and bubbles in the sight glass. If I find a dime, I’ll post a pic.
    If God didn't want us to eat animals... He wouldn't have made them out of MEAT.

  7. #7
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    I wish somebody would try the dime thing. I don’t believe it has ever been done. Wouldn’t the power element leak where it is threaded to the valve. Or flood the system. I don’t think a good power element diaphragm moves the thickness of a dime!
    Just don’t believe it will work and never found a dime,

  8. #8
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    Quote Originally Posted by rickl View Post
    I wish somebody would try the dime thing. I don’t believe it has ever been done. Wouldn’t the power element leak where it is threaded to the valve. Or flood the system. I don’t think a good power element diaphragm moves the thickness of a dime!
    Just don’t believe it will work and never found a dime,
    Done it twice. Gave time to get a replacement head.

  9. #9
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    Quote Originally Posted by rickl View Post
    I wish somebody would try the dime thing. I don’t believe it has ever been done. Wouldn’t the power element leak where it is threaded to the valve. Or flood the system. I don’t think a good power element diaphragm moves the thickness of a dime!
    Just don’t believe it will work and never found a dime,
    I’ve done it once, and a friend of mine was running a call recently, sent me a pic of one he found that no one knew how long it had been in there.


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  10. #10
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    Thinking about the dime trick, now I’m even more skeptical about changing the TXV. Because with a dime, the system runs semi-normally. Can anyone think of another reason I’d have high head, And low (no) superheat.
    If God didn't want us to eat animals... He wouldn't have made them out of MEAT.

  11. #11
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    I tried the dime thing once but it definitely was flooding back and I couldn't leave it like that. So I used shim material and tried a couple THINnesses lol and it worked out well for overnight.

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  12. #12
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    I did the dime trick once ... 10 oclock at night with cooler full of food

    The dime wasnt letting enough juice in , so I used a thicker washer

    It definitely doesnt work right , but it works good enough for the night

  13. #13
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    Quote Originally Posted by GenesisRefrig View Post
    Can anyone think of another reason I’d have high head, And low (no) superheat.
    I assume the juice is moving so fast through the system it doesnt have enough time to reject heat ....

  14. #14
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    Did this federal case have a tecumseh condensing unit and compressor?

    I dont like those tecumseh condensing units because the run their condensers real small so they'll fit in areas but that causes high head pressure.

    I've had a federal case like this and the Expansion valve liked to floodback. Had a receiver too and it ran real high head in a 73F ambient.
    Still kinda fighting it

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  15. #15
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    Quote Originally Posted by UmmScott View Post
    Did this federal case have a tecumseh condensing unit and compressor?

    I dont like those tecumseh condensing units because the run their condensers real small so they'll fit in areas but that causes high head pressure.

    I've had a federal case like this and the Expansion valve liked to floodback. Had a receiver too and it ran real high head in a 73F ambient.
    Still kinda fighting it

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    You’ve been to my job site! That’s it exactly.
    If God didn't want us to eat animals... He wouldn't have made them out of MEAT.

  16. #16
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    What is the Tecumseh condensing unit's model number?

    Go to Tecumseh Boxload page, select Condensing Unit Data Sheets and scroll down the dropdown menu to find the model. It'll give you what the condensing temperature should be.

    https://boxload.tecumseh.com/

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