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  1. #1
    Join Date
    Jan 2013
    Location
    Eaton, Ohio
    Posts
    6

    High pressure and high SH on Geothermal heat pump

    I have a Miami Heat Pump 3 1/2 T R-410A geothermal unit and I have high, high side pressure and high SH readings in heat mode on full capacity. On 1st stage the readings are normal. With de-superheater off and on full capacity and on heat I am running 415 psi discharge with 114 liquid temp for 7 degrees SC, 100 PSI suction and 48 degrees suction temp for 16 degrees SH. When the pressure gets this high I know it is costing extra to operate and harder on the equipment. According to diagnostic manual with the SC at near normal it indicates that the TXV is OK, which I assume means there is no restriction in the filter/dryer either. I measured temp of suction just above the RV going in at 48 degrees and coming out at 57-58 degrees, I read in another post that this was normal. According to the manual the normal SC temps indicate that the air coil is working normally. This unit replaced a 3 ton air to air heat pump that was in operation for 13 years with out trouble. I measured pressures on my son-n-laws 3 ton Century unit and it runs 95 suction and 325 discharge 1st or 2nd stage and only draws 7.5 & 10.75 Amps accordingly. I have practically lived with this unit for the last month, it heats fine; just mostly worried about the Amp draws and longevity of the unit. thanks---rick

  2. #2
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,564
    Sorry this is not a DIY site. If you're a pro then get your post count up and apply for pro status. Read the rules. Sorry

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,308
    How much duct work alteration did you have to do to increase to a 3.5 ton. Cause it sounds like you don't have enough air flow for it.
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  4. #4
    Join Date
    Jan 2013
    Location
    Eaton, Ohio
    Posts
    6
    Actually the original 3T had a 3.5 T coil and a 100,000 BTU furnace w/ 1500 cfm (on high ) blower as the back up system. It has 3 zones and the zones are configured so that 1 zone = 1st stage, 2 zones = 2 stages and 3 zones = 3 stages (on heat ) and the breakers for the electric heat are turned off. I have removed the by-pass damper fitting from the main plenum (opened it up to the basement ) and that did not change any readings at all. Seems to be normal amount of air flow out the registers. Is there an easy way to verify air flow or will I have to buy a new pressure gauge to read it ? I'm getting ready to retire and was hoping to not have to buy a new gauge but will if I have to.----rick

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,308
    Static pressure test is the easiest way. And nee a manometer to do it.
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  6. #6
    Join Date
    Jan 2013
    Location
    Eaton, Ohio
    Posts
    6
    beenthere, my unit is horizontal in my crawl (concrete floor) and connects to a 24"x 24" el turned up into my plenum. Today I cut a 20 x 16 out of the end of the el in line with the blower output basically dumping everything into my crawl. Low side stayed steady and discharge pressure dropped a few pounds, ---basically nothing changed. In case you wonder I also pulled the 25x20x5 filter out to relieve return air, I have large R/A so this made no difference either. Diagnostic manual says if there was a restriction the SC & SH would both be high or if the TXV was stuck open both would be low, it has no option for normal SC with high SH. Although unit is keeping the house warm the HE is low also. I have 10gal/min water flow at 54 degrees off a well. TD is around 5.5 in heat, I am stumped. We just dropped into single digits here in Eaton, Ohio w/ wind chill below zero, it's cold!--------rick

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,308
    Should have left filter door off when you did that.
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  8. #8
    Join Date
    Jan 2013
    Location
    Eaton, Ohio
    Posts
    6
    I did leave the door off for the test--------rick

  9. #9
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,395
    What are the sh and sc expectations?

    If it is high sh and high discharge pressure, I would slow the water down a bit. Is the h2o delta correct?

  10. #10
    Join Date
    Jan 2013
    Location
    Eaton, Ohio
    Posts
    6
    6-12 SC, like to see max 14 on SH, I don't know the term delta on water, I have a flow meter in line and have slowed the water down by throttling the ball valve on several different occasions but it doesn 't change anything.--------rick

  11. #11
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,357
    You need to know the static pressure this unit is operating under, and that when it's not taken apart in an attempt to improve airflow. Manometers are not that expensive. Eliminate one possible source of the problem before concentrating too hard on another possible source...way too easy to conflate things during troubleshooting. If you want to eat a huge sirloin steak, how do you do it? One bite at a time. Gathering lots of data will help you get this problem eaten.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  12. #12
    Join Date
    Jan 2013
    Location
    Eaton, Ohio
    Posts
    6
    shophound, I don't understand if opening it up to basically 0 pressure doesn't change it then why will having the accurate readings tell me anything? Am I correct in assuming the TXV can't cause this problem? -------rick

  13. #13
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,357
    Do you have any assurance it is correctly charged?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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