Multi-zone Mitsubishi system is not performing with all zones running
Earlier in the year I had a four zone Mitsubishi system installed. Since the install wrapped up I’ve been chasing performance issues which my contractor has not been able to get to the bottom of at all.
The system consists of:
2x MSZ-FH09NA (Kitchen and Sunroom)
SVZ-KP24NA (Bedrooms and Bathrooms)
The ductless units have generally performed well from the start, but the SVZ air handler has never been able to hold a set point or adequately remove humidity. Oftentimes the supply and return temperatures for the air handler are within a couple degrees of each other or exactly the same.
Yesterday I discovered that the problems with the air handler go away completely if it is the only zone running. Currently with just the air handler running I’m seeing temperatures of 53°F at the supply vents and 71°F at the return vents.
Has anyone out there experienced a similar issue? Previously I was thinking that there was maybe a kinked lineset going to the air handler or a faulty LEV in the branch box, but now I’m starting to think it’s simply undercharged. FWIW, the weight of the refrigerant the contractor provided matches up nearly exactly with what Mitshibishi’s Diamond System Builder gave me when I plugged everything in with ballparked lineset lengths.
I’ve attached a screenshot of some data logs for the last 24 hours. Notice that around 6AM today when I turned on the floor unit in the office that the supply temperature for the air handler began dropping off almost immediately.
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