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Thread: Rheem HP bouncing off HP limit

  1. #1
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    Rheem HP bouncing off HP limit

    This old Rheem RQPL package unit (R410A) works great in cooling but has unsteady high pressure in heat mode. The discharge pressure sort of levels off in high 300s/low 400s then over a few minute time span it will creep up to a brief touch of 700 PSI and then drop back down to low 400s. Then, it will creep up creep up and then relief again. It doesn't drop off suddenly but drops down slowly at the same rate as it was climbing before.

    I reckon it is crap in the system and that changing the outdoor TXV + drier will solve the problem... but this is the first time I have seen a txv act this way, maybe it is not contamination but another type of txv failure?. The motor (bulb) is properly attached and insulated.

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    I would be inclined to check the blower capacitor and amp draw just to be sure the blower is not on the verge of quitting and maybe not moving enough air.

    Sent from the Okie state usin Tapatalk

  3. #3
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    Start with the basics. Is the indoor coil clean? How is the airflow over the indoor coil? Filters?
    If God didn't want us to eat animals... He wouldn't have made them out of MEAT.

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  5. #4
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    What is your superheat and subcooling showing as?

    Temp split across the evaporator?
    Quickly, I must hurry, for there go my people and I am their leader!

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  7. #5
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    In heating mode it never got stable enough to get a reading. Thats what I was zeroing in on. Up/down up/down I'll be going back today to verify evap condx and evaluate whether the unit is worth investing in.

  8. #6
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    Quote Originally Posted by Tom Thermo View Post
    In heating mode it never got stable enough to get a reading. Thats what I was zeroing in on. Up/down up/down I'll be going back today to verify evap condx and evaluate whether the unit is worth investing in.
    What are the temps on all four pipes of the reversing valve?
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  10. #7
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    I didn't measure the temps but there was no apparent mixing i.e. hot and cold, no warm. Switched hot and cold no problem. Heat worked, ac worked, but heat pressure unsteady. I'll look more at that if I can during the transient. So you're saying maybe the reversing valve is wandering and restricting the compressor discharge flow.

  11. #8
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    Sounds more like a slight over charge, and non condensables in it.
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  12. #9
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    Quote Originally Posted by beenthere View Post
    Sounds more like a slight over charge, and non condensables in it.
    BINGO

  13. #10
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    OK I'll go get the numbers in cooling mode. We're going to get to the bottom of this yet! haha It has been running without issue for years but maybe the 700 psig overspikes finally woke up the problem.

    It could be the exuberator valve.

  14. #11
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    I just checked my records and I have never put gages on this unit since I have been maintaining it since 2017. Time for JobLink and my exuberator adjuster.

  15. #12
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    410a HP limit is typically set at 600. Why is this system running up until 700? What is the switch set for?
    Quickly, I must hurry, for there go my people and I am their leader!

  16. #13
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    OK there is no switch. Smooth sailing in cooling mode but as soon as that reversing valve switches over the discharge pressure goes to 700. Maybe an internal pressure relief opens?
    gotta go

  17. #14
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    You are giving it five minutes off time before switching between heat and cool correct

  18. #15
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    Negative pec. Thanks. it minor spike at switchover, then rises to peak 700 then drops back down to 420 then slow rise back to 700 and slow back down. One minute cycle. I am confident this thing has not been doing the same thing for 3 years. Interesting I can see the same 1 minutes cycle on much
    smaller scale in cooling mode

  19. #16
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    It must be kicking out on thermal overload. I haven't seen that yet, imm too scared to let it go that long. The call was for no heat. But ac, 8 SH ... 34 Deg sc

  20. #17
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    Test forum update new fone

  21. #18
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    Quote Originally Posted by Tom Thermo View Post
    Test forum update new fone
    Coming in loud and clear.

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  22. #19
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    I vote for a dirty indoor coil
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  23. #20
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    Quote Originally Posted by Tom Thermo View Post
    It must be kicking out on thermal overload. I haven't seen that yet, imm too scared to let it go that long. The call was for no heat. But ac, 8 SH ... 34 Deg sc
    It looks Overcharged For sure (High SC standing out) with an odd restriction possibly at the filter dryer. It would be kicking out on high head, thermal OL would be if the CFM stopped..

    Remove the sensing bulb first, if it clears up your on the Right track...Try recovery of some of the refrigerant from the high side before the filter dryer.Ive seen lots of partial restrictions confuse other techs to adding refrigerant when the looked at the low side...

    Is the condenser clean and CFM not running backwards?
    Last edited by Unlimited1; 10-20-2020 at 09:48 PM.

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