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Fujitsu 18rflcd

User avatar
raul4817 | Posted in General Questions on

I have my fujitsu installed and currently up and running. 

I have notice that is tends to short cycle quite a bit. 

Not sure if this is normal operation but when I have it off for long stretches it will run for a good while to get the temp to set point. But after that I noticed that it tends to run for a minute or so every 5min throughout the day sometimes even closer increments . Temps are fine and no worries there. 

Yesterday I had it off most of the day as I was creating a bit of dust. I turned it back on before bed and it ran for a good hour or more to bring the temps down. Now back to the same short cycling. 

I did set the unit to high insulation and have not messed with the temp correction settings but it is off by about 2 degrees F. 

I’m getting no errors and its quite comfortable. Just was under the impression that this unit would variably modulate dow to 3k btus.

It has been quite mild but noticed it does the same even with temps in the 90s

Raul

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Replies

  1. User avatar Expert Member
    Dana Dorsett | | #1

    Which wall-remote/thermostat model are you using?

    Whichever model, I believe most (or all?) can be to programmed to use a temperature sensor in the remote/thermostat rather than sensing the return air temp at the air handler/cassette. The temperature of the return air can change fairly quickly compared to the average room temp, and can cause it to short cycle, or experience temperature offsets.

    Look for an " “ECONOMY / THERMO SENSOR” button on the remote. The default setting is "ECONOMY" which uses the sensor in the RLF cassette. When in ECONOMY mode, holding the button in for a couple of seconds toggles it into the THERMO SENSOR mode, sensing the temperature at the remote.

  2. User avatar
    raul4817 | | #2

    Dana,

    I believe I have the wired remote UTY-RNNUM. I will verify in the morning. I change the function setting to sense at the remote, I forget the function setting number. This seemed to help. I tried to use the thermo sense but was greeted with a lock key. The manual says to call your service tech if this is the case.

    Today was 95f so it ran a longer today.

    I have also noticed no condensate draining from the unit for quite some time. During the cooler days that it short cycle I figured it didnt run long enough to pull any moisture, but today it ran a good while and nothing.

    I checked my drain pitch and even poured some water to verify I had no blockage.
    My RH was around 48% today but it's been around 43%. On my initial startup it took a while but it did drain some condensation now I haven't seen a drop in almost a week. Just curious if this is normal behaviour, perhaps there is not enough moisture to remove?
    Raul

  3. Andy CD Zone 5 - NW Ohio | | #3

    Raul, is it possible the unit is way oversized for the space you're cooling? That would lead to all the problems you're describing. Of course, no condensate draining is a serious worry--unless humidity is already low. What's the weather outside, other than just hot?

    1. User avatar
      raul4817 | | #5

      yesterday was around 91F and 60% RH at noon, and 81F and 85% RH later that evening.

      The AC is oversized due to the heating load needed. My engineer called for just over 10k btus in cooling and 16k btus for heating. I mainly selected this unit for its modulation down to 3k btu hoping it would help with longer runtimes even in my case where the unit is oversized on the cooling side to cover the heating demand. I almost went with the 15rflcd but figured with the same min. modulation specs it would be similar in efficiency. I should note that i have yet to hang drywall yet so is it possible that once separating bedroom walls go up that the unit may need to run a bit more to properly mix the air temps to satisfy the wired control.

      Raul

  4. User avatar
    Jon R | | #4

    If you want longer run times, you can increase thermostat dead band by insulating it. For example, lay a cloth over the remote.

    > My RH was around 48% today but it's been around 43%

    Inside or outside?

  5. User avatar
    raul4817 | | #6

    Jon,

    This is the interior RH. Outside yesterday was between 60% to 85%.
    I changed a few function settings, I selected high insulation and lower my static pressure back to the factory setting of .1

    current indoor temp is 72F and 45% RH. The unit is set to 74. I did a temp correction in the function settings because I was consistently under my temp point by 2 degrees. It did help some. The past few days I have been under my temp setpoint be 1 degree. This morning was 2 degrees but it did cool down quite a bit last night.

    Raul

    Raul

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