New Heat Pump Saga Help!

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New Member
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Halifax, Nova Scotia
Fujitsu 24ARU24GLX Medium Static Duct installed - 6 outlets, 2 returns, in attic, serving upstairs bedrooms.

Is unable to get temperature down in top floor and stays on.
It works great for a couple of days and then is unable to reach set point even though its actually cooler outside then what I am asking.

Symptoms: The white plastic cover running over the insulated ducting and electrical wiring up to the attic on the outside of the house ( approx 30 feet) is sweating (large drops of water, although the sun is out and all siding is dry and did not rain).
Symptoms: The inside insulated ducting is sweating all along its length to the attic unit approx 25 feet.
Symptoms: If left to progress, like I did the first time, the sweating gets heavier and the ability to cool diminished.

Facts: The unit comes with 4lbs 10ounces (74 ounces) of R410 and is rated to a pre-charged length of 65 feet. The condensate drain hose does not leak and expels water properly (gets pumped up by internal Fuji pump about 3 feet)

First Tech call: Checked pressure and it was slightly under 100, which apparently is equivalent to around 0 to -1 degree, Celcius. He said it should be around 120-125. Tech thinking there was not enough refrigerant added first 4 ounces, no change, and then an additional 14 ounces for a total of 18 ounces with no change on pressure reading. Turned unit off.

Second Tech call: Came and noted pressure was still less than 100. They removed the refrigerant to weigh it and it came close to the expected 74+18added= 92 ounces. It came to 86, but they lost some ounces when connected the hoses up. The conclusion was that there was no leak. Since the stock lines come at 50 feet, they had to braise an additional 5-10 feet of copper. The techs checked both braises and the fittings at the unit in the attic with soapy water. They had purged all the refrigerant out for weighing and used Nitrogen to do the leak check. (also helps clean the lines?). In any case there were no leaks detected in the usual spots.

The techs then removed the nitrogen and replaced it with the factory setting amount 74 ounces of refrigerant. The pressure came up to 125 (around 6-8 degrees Celcius) and they were happy about that.

They could not explain what happened but surmized that with the pressure/ temperature being
lower than expected, freezing within the system could occur and cause all kinds of problems.

I restarted the unit and the first day it seemed to work fine, the second day it could not meet the setpoint again, despite a cool evening and thus instead of waiting for a couple of days and playing with fan speed etc.. I checked sooner and found the same symptoms although not quite as much sweating and droplets but well on its way there. I called for assistance and turned the unit off, again.

They plan to send out a tech on Friday.

After some reading, I am at a loss as they are to explain it. The literature says that cold air at approx 20 degrees less than the setpoint should come out of the outlets and quickly do the job. However it does not so the system stays on for a long time, I suppose trying to reach the setpoint and the result well is moisture in the attic, which is not acceptable.

Any ideas, thoughts, pointers welcome as the third Tech call is going to occur. :-(


6th clinical trail chemotherapy 5/15/24
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Orlando, Florida
Maybe a bad expansion valve. I never worked on a mini splits but as a norm there only the low pressure side can be measured for pressure. Since the symptoms seems to be low pressure, I'm suspecting an expansion valve in one of the cassettes is not regulating and allowing too much refrigerant to past (stuck open perhaps). The refrigerant may not be expanding to gas well after the coils and causing the return line(s) to be too cold thus sweating. I'm not 100% on this but the symptoms of sweating lines seems to indicate it.

Please run this by the service tech and update this post when the problem is resolved.


Well-Known Member
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Peace valley missouri
Are both refrigerant lines insulated? That pic of the lines look like there in a plastic sleeve. Both lines run cold and will sweat being under the dew point. Are there any sharp bends that a line could be kinked like where it enters the house. Whats the model of the outside unit.
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