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Thread: Heat Pumps

  1. #1
    Join Date
    Feb 2005
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    Dothan, Al
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    Can anyone explain to me why heat pumps trip off on the high pressure switch, when there seems to be no problem.
    Every spring & fall, we have several calls where heat pumps have tripped on high pressure switch.Start up unit & head pressures are good ( not even a little high ).
    This seems to be occuring mostly when cool in the mornings and hot in the afternoon. In other words, when switching between heat & cool.
    A lot of these are Rheems but have seen others do the same?
    I hope ya'll can help, as I have been in the dark for years about this. Oh yea, have verified that switches are not tripping prematurely. Have run tests trying to duplicate problem but still cannot get the switch to trip.

    Any & all help would be appreciated.

  2. #2
    Join Date
    May 2000
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    Indianapolis, IN, USA
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    33,901
    We usually find it in people with plugged filters. Doesn't hurt cooling mode but when they first heat in mild weather, the restriction is enough to trip it. We have one guy who uses it as a reminder when to order a new media

  3. #3
    Join Date
    Jul 2004
    Location
    West TN
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    983
    Cycle timer or a digital stat with the cycle timer built in.

    Next one you go to... get the system running in heat pump mode... once the pressure settles down, kick it over to Air Cond... watch your pressures.
    Then try the other way around.
    Putting in a cylcle timer on should let the pressures settle down before switching over.

    Also... are these duel fuel heat pumps?
    Trane's older duel fuel kits had a temperature switch that would monitor the temp of the furnace air blowing across the coil when in a defrost. If the air temp got too high it would cause the indoor coil to absorb too much heat making pressure go up.
    Grant it this is a remote possibility given the outdoor conditions you've mentioned. Don't sound like the right time to go into defrost hehe. But, nonetheless, a good bit of info to store in the back of your mind.

    Extend to others the grace that God has given you.

  4. #4
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    Feb 2005
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    Dothan, Al
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    Bald - of course the filters could cause - but in these cases & whats got me stumped, is that I can find no apparent reason, cooling or heat cycle for it.

    Wormy - I know that the last two that did this had electronic boards with tme-delay features. I have switch from heat to cool and from cool to heat, but still could not make the system bring the pressure up even close to hp cutout.

    Thanks guys for your responses.

  5. #5
    Join Date
    Mar 2002
    Location
    Richmond, Virginia
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    4,264
    Make sure your defrost thermostat is making good contact with the tube. I've seen them get turned a little causing the groove in the switch to not fit well, which can prolong defrost allowing pressures to trip the switch. Compounded by warmer outdoor ambients.
    There is nothing more frightful than ignorance in action....Mark Twain

  6. #6
    Join Date
    Nov 2000
    Location
    Upstate, SC
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    2,919
    Originally posted by HVAC Pro
    Make sure your defrost thermostat is making good contact with the tube. I've seen them get turned a little causing the groove in the switch to not fit well, which can prolong defrost allowing pressures to trip the switch. Compounded by warmer outdoor ambients.
    Yeah, I am thinking something to do with the defrost too. I have been out on two calls tripping on high head lately that the residential techs were having problems with and found both to be problems with defrost. One had the wrong defrost termination switch on it that was causing it to stay in defrost too long and the other was a problem with position of the switch on the tube.

    Bobby

  7. #7
    Join Date
    Apr 2004
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    7,680
    More often than not you will find this happens "Randomly" on units with no filter driers. The Rheem Systems were matched tightly to provide good HSPF. The slightest moisture in the system can cause a temporary blockage large enough to offset the circuiting.

    Verify a goos system match
    Verify airflow is within 10% of nominal
    Verify Proper line sizes and lengths and vertical seperation

    If all that is ok. Frost the coils to see if you have a restricted circuit.

    If still ok, Recover refrigerant, install drier, tripple evacuate breaking the first 2 with nitrogen and the third with refrigerant, and recharge using virgin refrigerant.

    Odds are you will see your problem go away.

  8. #8
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    Feb 2005
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    Dothan, Al
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    Ok I guess you guys have not had the same problems with the heat pumps.
    The ones I have problems with are only tripping their high pressure switches one or ( at the most ) two times a year.
    At least on three of them last year, have had no further trips.
    Have two or three units that trip one time every year but will always be in the fall or spring.
    Have thought about defrost problems, but these happen so infrequently.
    Could be a combination of defrost and higher outdoor temps.
    Thats why I was trying to see if any of you guys had noticed the same problems - I guess not

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    I've had that same thing on Rheems, coils clean, charges is right, can't find a reason.
    Mostly in the spring.

    My solution was to bypass the manual reset, and install an automatic resetting hp limit.

    You may begin the beating on my bald head now DOC.
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    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Apr 2004
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    bornriding, I am speaking specificly about the jobs you describe. If it is as intermitant as you say and you have verified airflow, match, piping and all that. Do the latter part with triple evacuating, drier etc. and it is likely you will not have the problem again.

    Can you tell me is there a drier on these jobs?

    Alot has to happen just right for this to be an issue. The mosture will eventually collect in the circuits of the outdoor coil or at the TXV and run the pressure up intermittantly. After the unit shuts down, the moisture thaws and disipates back into the system only to creep up later. Remove it and your intermitant problem will go away.

    BTW, dont just add a drier and think that will solve an exsisting issue, do it right. But a drier on new systems is just good practice as is a proper evacuation.


  11. #11
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    Feb 2005
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    Dothan, Al
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    Doc

    Don't know about the dryers. Thats one thing I never thought to check. Will start looking at that. Since it is fixin to be spring, I know we'll have 6 or 7 to happen in the next few weeks, so I will see if the dryers are there or not.

  12. #12
    Join Date
    Apr 2004
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    When it happens, do as I say and see for yourself even if it does have a drier. But I am thinking it mostly happens on systems where they werent used and someone wasnt too concerned with best practices like changing their vacuum pump oil more than once a year.

    Keep us posted.

  13. #13
    Join Date
    Jan 2005
    Location
    daytona florida
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    76
    i have seen in many of rheem and ruud systems problems of the same i have done tripple evacs and sometimes it works i have also found that the piston in the outdoor unit had trash restickting it's flow not to say thats your problem but ive seen it some installers unfortunatly did half/ss work bad for them good for me

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