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Thread: TXV frustrations

  1. #1
    Join Date
    Mar 2001
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    TXV frustrations

    3-ton, 16SEER Goodman with matching TXV evaporator on a 96% upflow furnace. I installed the system 7 years ago and it had been working fine, no service calls from the customer the whole time. They got a coupon for a "$29.95 A/C tune-up" from Brand X who sent a "tech" out to tune-up the system. He charged my customer for 3# of R410 and left. Total charge on the system is only about 6#. The customer called me a week later and said their a/c wasn't working correctly, it wouldn't maintain temp in the house. I discovered the high side pressure was low, the low side was high and the compressor was really noisy. So I shut off the liquid line to see if it would pump down which it would not. If it was a piston compressor I'd say it had been slugged--can scroll compressors get slugged? The compressor was beyond the warranty so I replaced the condensing unit. I installed a liquid side filter/dryer, checked for leaks with nitrogen then pulled a 29.9xx" vacuum which held for about 40 minutes. I broke vacuum with R410, opened the service valves and started the system. Here's where things get weird: the high side pressure went up like a rocket, 650#+-, while the low side started going down then went way down: saturation temp about 25f. The high side eventually came down but was still too high. Ok, a restriction in the system. It's a short line set: 12'. I pumped it down again, removed the TXV and blew nitrogen through both the low and high sides. No debris came out so I assumed the TXV was stuck. I replaced the TXV and started the system again. It did almost the same thing but the high pressure didn't spike quite as high. I took the TXV sensing bulb and put it in a little tub of hot water and the pressures normalized and the system started cooling like crazy. I put the sensing bulb back on the suction line and it did the same thing: high pressure spike and extremely low suction pressure. So I left the sensing bulb dangling but I don't want to leave it that way.

    Any ideas?

    Rich

  2. #2
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    A scroll compressor will have low discharge and high suction when flooding. Recover charge to correct and usually ok.

    Bi-flow filter drier?
    Pumpdown test for non-condensables?
    External equalizer line plugged?

  3. #3
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    Thread Starter
    I thought about the equalizer or sensing bulb tubes being kinked or the equalizer tube Schrader valve not opening so I checked them both before I replaced the TXV. It still doesn't answer the question as to why the pressures are mostly correct with the sensing bulb dangling and wrong with it attached to the suction line. I'm confused...

    Question: will a scroll compressor pump liquid? I've never tried it...

    Rich

  4. #4
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    29" vacuum is worthless get a micron gauge!

    I see no SH or SC #'s whats up with that?

    Was the factory drier in the outdoor unit removed? (if equipped)

    You had the valve out should have just replaced it!

  5. Likes Bombboy90 liked this post.
  6. #5
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    I'll have to check my notes for sure but off the top of my head superheat with the sensing bulb attached was around 25f, subcooling was ~12. With the sensing bulb in hot water superheat was ~9 and subcooling was ~8. Indoor RH was ~40% (she'd been canning) and 76*f TD across the evaporator with the sensing bulb attached was ~10f, with it in hot water was ~ 18f. Outdoor temp was ~91* and <10%RH.

  7. #6
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    Did you purchase a new TXV .... or simply blow thru the old one and re-install it ?

  8. #7
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    Is the new condenser a microchannel type? very sensitive to even slight overcharge..
    "He who knows the least, knows it the loudest"
    I'm not young enough, to know everything...

  9. #8
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    What's the temperature of the suction line where you are attaching the bulb?

    As someone said get a micron gauge - maybe still got some non-condensable in the system?

    I wonder what the tune up guy did when he added extra refrigerant. Sounds like he contaminated the system somehow.

  10. #9
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    The other person prolly put stop leak in and that crap is hung up in the screen before the txv?

  11. #10
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    Why dont you adjust your txv. Alot of goodman txv usually need adjustments even if they came from the factory already set.

  12. #11
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    Quote Originally Posted by Hurst11 View Post
    The other person prolly put stop leak in and that crap is hung up in the screen before the txv?
    Probably doesnt matter because he already replaced the txv and the outdoor unit. Just the coil is still original. Btw, too bad you never registered the equipment. For a system that is 7 yrs old they could have still had the 10 warranty .

  13. #12
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    How's your ductwork and filter. I've seen strange stuff going on just because of a plugged up filter.

    Sent from my VS988 using Tapatalk

  14. #13
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    Quote Originally Posted by mofotech View Post
    Probably doesnt matter because he already replaced the txv and the outdoor unit. Just the coil is still original. Btw, too bad you never registered the equipment. For a system that is 7 yrs old they could have still had the 10 warranty .
    Just because the txv was replaced doesn’t mean the screen before the valve ain’t stopped up. That’s what I’m bettin on anyhow. Whatever is in the screen needs cleaned out or replace the screen.

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  16. #14
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    I discovered the high side pressure was low, the low side was high and the compressor was really noisy.
    When you arrived the comprerssor scroll plates had seperated ( a safty built into the compressor) . It was efectively not pumping .
    the high side pressure went up like a rocket, 650#
    2 things happening here. # 1 its overcharged from the previous guy #2 your txv has lost moof the charge in the powerhead causing a closed valve condition.
    Replaceing the txv and adjusting the charge( remove) would have solved the problem.

  17. Likes mofotech liked this post.
  18. #15
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    Mar 2001
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    Thread Starter
    I installed a brand new TXV.

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