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Mitsubishi MXZ-5C42NA2 – defrost with no ice?!

m_sea | Posted in General Questions on

I am in Seattle, and have a 4 head Mitsubishi 5c42NA2  (6,9,12,15k FH heads) system. While the temperature output is fine, the defrost behavior of this unit is bizzare:

1. Main concern: Doing a defrost cycle with ZERO ice on the outdoor unit, not even a drop of water coming out by the end of a defrost cycle at 36 degrees, in low humidity conditions.
2. Defrosting at 45 degrees
3. One time when I got a few inches of snow, it froze solid and would not call for a defrost (lol) – had to put the unit into cooling mode for it to work

The techs once overcharged the unit to 11 lb 6 oz, then they removed all refrigerant and weighed it in again at around 8lb+ I believe. I have about 170 ft of lineset and ~30ish bends.

The techs also checked the resistance of a few thermistors – I don’t remember if they did them all, but the ones I saw them check, looked correct.

While I am learning to live with the awful diesel truck idling sound when the unit is heat mode, this whole defrosting with no ice nonsense is frustrating.

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