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Symptoms of low refrigerant

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THETRUCK454
THETRUCK454 Member Posts: 37
edited June 15 in A-C, Heat Pumps & Refrigeration

I installed a system in my house that's in the thread below. I ended getting cold feet (pin intended) when it came to flare the lineset ends and purge/dump the coolant so I hired an HVAC tech to finish that. All the literature said the unit is pre charged for up to 50' of lineset, I have about 8' left over from a 50' roll. Sticker on the outside unit contradicts the literature and says it's only pre charged for 25'. The HVAC tech did not add any refrigerant because he never does for units this small size. What symptoms or diagnosis can I do myself to see if I need more?

I ask because I am having high humidity in the house, 65-70%, but it will chill it down to 68 and keep it there no problem. I put it on dry mode and let it run over night and temp got to 63 and RH was 62%. I know high RH is a sign of an oversized system, but could it also be a sign of low refrigerant? For info, for now outside temps peak at low 80's during the day and low 60's at night.

https://forum.heatinghelp.com/discussion/201703/mini-split-location

Comments

  • mattmia2
    mattmia2 Member Posts: 17,409

    does the whole evaporator get cold? you could measure the subcooling but if the whole evaporator is getting cold the superheat is probably staying where the expansion valve is set to keep it so the evaporator won't get any colder than it is.

    it is probably oversized. if there is a way to limit the maximum capacity that the compressor runs at if it is a modulating system, slowing that down could help with dehumidification.

  • Ironman
    Ironman Member Posts: 7,926
    edited June 15

    Check and see if the vapor (larger) line gets cold and sweaty after the unit has been running for 10 minutes. If so, the charge is probably okay and I’d trust the label on the unit over the literature.

    A small single zone mini split won’t have a liquid line between the indoor and outdoor unit: the smaller line is downstream of the electronic expansion valve and contains saturated low side refrigerant. So, you can’t check sub cooling there.

    Usually, the fan on the indoor unit will run continuously because that’s where the return air sensor is. This can cause any water on the coil or in the drain pan to be evaporated back into the air. It’s usually not an issue, but check that you drain line has continuous slope and is not trapped anywhere.

    How did you determine what size unit was required?

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    HydronicMike
  • THETRUCK454
    THETRUCK454 Member Posts: 37
    https://forum.heatinghelp.com/discussion/comment/1898598#Comment_1898598

    I determined the size based of my crack at a manual j calculator and then input from people in my original post. There was quite a lot of controversy on size in that original thread for the square footage the 15k way high, yet when you add it all the exterior windows/walls and the fact that the whole end of the house is open concept with a kitchen it started to make some sort of sense. I was between the 12k and 15k, ultimately went with the 15k because per the literature it said it was pre charged for up to 50' vs the 12k was pre charged for 25'. I knew I'd be over 25' lineset so that was the tipping factor. Course after I got into it I had a HVAC tech do the final connection that concern should have been a mute point.....

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 20,461

    @THETRUCK454

    The old rule of thumb was 600 square feet/ton but with modern construction that is probably too much.

    appliances, people, amount of glass, blinds or trees (shading) building construction and insulation all play a role in the cooling load.

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