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  1. #1
    Join Date
    Feb 2008
    Posts
    15

    Restriction Or bad TXV?

    I'm Working on a Lennox split system unit With an intermitting problem. First time I got called, the unit was operating properly.Two days later I get called again, I connected my gages and the suction kept sucking down below 50 psi and the high side went up to 400 Psi and kept climbing. So I shut the unit down, the compressor would of went out on over load any way. Went to check if I had air flow, That was ok went out side to turn the unit back on And the unit started working properly again. Can't find any thing wrong.I know there going to call me out again. Any suggestions Thank you in addvance.

  2. #2
    Join Date
    Jul 2007
    Posts
    20
    is this a ac or a heat pump

  3. #3
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,989
    If it is an A/C, not a heat pump.
    This is just a guess from here; possible moisture in the system that is freezing at a point where it causes a restriction.

    When the system shuts down it thaws & works normal until it freezes again.
    It sounds like "some kind" of intermittent restriction.

    Edit: Look for a frost area. The strainer/screen ahead of the TXV could be partially restricted, - with moisture in the system, it could ice-up.
    Last edited by udarrell; 06-24-2008 at 07:01 PM. Reason: check strainer/screen ahead of the TXV

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,095
    Don't take this too wrong.
    But besides putting guages on, and some sort of air flow check.
    What else did you check.
    What kind of metering device.
    A/C or HP
    Amps and voltages of all outdoor motors.
    Air and line temps.
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  5. #5
    Join Date
    Feb 2008
    Posts
    15
    It's a heat pump. I think my problem is with the TXV in the evap coil. But like I said it's an intermitting problem. That's why I'm confused Any help is apreciated, Thank you.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,095
    Next time they call, keep it running and look where the frost begins, thats usually the restricted area.
    It could be the TXV, or something it the line some where.
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  7. #7
    Join Date
    Feb 2008
    Posts
    15
    Quote Originally Posted by udarrell View Post
    If it is an A/C, not a heat pump.
    This is just a guess from here; possible moisture in the system that is freezing at a point where it causes a restriction.

    When the system shuts down it thaws & works normal until it freezes again.
    It sounds like "some kind" of intermittent restriction.

    Edit: Look for a frost area. The strainer/screen ahead of the TXV could be partially restricted, - with moisture in the system, it could ice-up.
    I did check for any freezing, But at the time I checked didn't find anything. I do agree with you, so I Will replace the expansion valve and install a biflow dryer filter.

  8. #8
    Join Date
    Feb 2008
    Posts
    15
    Thank you Beenther, I will let the unit run and check for any freezing before replaceing any thing. Once again thank you for your help.

  9. #9
    Join Date
    Oct 2007
    Location
    Southern Indiana
    Posts
    94
    Normally with a txv or liquid line restriction the head pressure will run low not high, the mass flow of refrigerant is down so compression ratio will be down. I would check with the cust. and make sure someone wasn't there before you and misdiagnosed it as being low on charge and dumped a bunch of gas in it, causing the head pressure to go so high.

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,095
    With that head, and that vapor, it pretty much tells you someone has added gas in the past to keep it from freezing instead of trying to find the problem.

    Never hurts to ask.
    But if cousin Dave put the extra gas in. Customers sometimes will tell you no one addded any gas.
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  11. #11
    Join Date
    Jan 2008
    Posts
    16
    Interesting thread. I have a 6 year old Trane XL13i with the appropriately matched air handler for the upper level of my colonial that couldn't keep up with the heat wave a couple of weeks ago. I waited for the post heat wave rush to subside before calling two gentlemen referred to me by an aquaintance in the building trade.

    They noted that the pressure was low initially but then started to rise to a decent level. After a few minutes the pressure began to slowly drop.

    The indoor filter is clean and they observed that the coil was clean yet a little rusted. They used leak detectors and couldn't find any trace of a leak anywhere around the indoor and outdoor units.

    Their diagnosis is that it's unlikely to be a blockage because the drop in pressure would be sudden and not gradual. They believe the problem to be the TXV and recommended replacing it and the coil at the same time to reduce labor hours and because it's not in great shape anyway. They also recommended installing a dryer filter.

    Any thoughts, lads?

  12. #12
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,095
    What they were seeing is know as hunting.
    Its not always a problem with the indoor equipment.

    So they may be right that the TXV needs replaced, or they could be wrong.
    They are right it does need a FD installed once they open the system up.

    If they are sure it will fix the problem, or they will fix the real problem for free, let them do it.
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  13. #13

    Confused

    Funny I have a similer problem but the liquid stays in the sight glass so I'm thinking its the metering device. Any ideas?

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