Virginia Miami HP cut out on low pressure

Discussion in 'Maintenance and Troubleshooting' started by nc73, Dec 31, 2014.

  1. nc73

    nc73 Member Forum Leader

    I have a 3 ton Miami HP hpx series with 2100ft of ground loop. Yes I wish I had never bought it. They have no pressure charts for this particular model, the one they told me to use was for a water to water model. In any case it cuts out in second stage right at 80psig when ewt is 41 or lower. The pressures they listed for 40 ewt was 68-83, yet their pressure switch is 80psig!! My flow center is single pump, and looks like its only outputting 2 gpm per ton. I know it's low but I didn't think it was too low to affect heating. In any case I ordered a two pump one. Will increasing flow help me at all? I really don't want to go back to pump and dump. Operating pressures in heating mode is around 89 suction 322 liquid. Superheat is kind of high, it was 25 before it cutoff. subcooling normal. It didn't get a chance to run long enough for me to get the values to stabilize. I hope it's not the TXV.
     
  2. nc73

    nc73 Member Forum Leader

    I'm thinking this thing is really meant for open loop. There is no fancy control board to change from open loop to closed, etc. They are sending me a new lower pressure switch. I'm going to install the 2 pump flow center to increase flow to where it should be regardless.
     
  3. Bergy

    Bergy Member Industry Professional Forum Leader

    A 3 ton closed loop requires 3 GPM/ton, or 9 GPM
     
  4. nc73

    nc73 Member Forum Leader

    Yup. I just didn't want to upgrade. I'll use the 1 pump flow center for my garage build this spring. In the meantime they've instructed me to bypass the pressure switch. It's running just fine now.
     
  5. Bergy

    Bergy Member Industry Professional Forum Leader

    R-410A @ 80 psi is saturated at 21 degrees. The person advising you to bypass the pressure switch has put you at risk of freezing your heat exchanger.
    If you split your exchanger, your warranty will be voided because you've altered a safety feature and the person advising you to do so will have no memory of telling you to do it. Get the issue fixed FIRST.

    Bergy
     
  6. nc73

    nc73 Member Forum Leader

    Actually I have the email from their support telling me to do so. The psig spec is still within their operating pressures, that's why they're sending me a lower psi pressure switch. It ran all night without a hiccup at 39 ewt and 30 lwt. I need to increase flow for sure with that delta.
     
  7. nc73

    nc73 Member Forum Leader

    So I got the QT 2 pump flow center installed. Everything works as expected except Delta on first stage changed from 6 to 8, 2nd second stage remained at 10 degrees. I'm now getting 9.5 gpm, both pumps running on medium.
     
  8. Bergy

    Bergy Member Industry Professional Forum Leader

    Did you put the pressure switch back in line?
     
  9. nc73

    nc73 Member Forum Leader

    Not yet. I'm going to test pressures in second stage today and see if it goes below 80.
     
  10. nc73

    nc73 Member Forum Leader

    Tested pressure and it's between 78 and 79 suction side. It will still trip the low pressure switch. I do have antifreeze protected down to 20. Although vsat was at 19-20.
     
  11. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Possible charge or metering device issue.
     

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