X-Trac 2.1 Controller
MX1 & MX2 are the DC Voltage to the Modulating Valve. O VDC will be full fire and 24 VDC would be minimum fire.
When temperature reach -22f/-30c MUA would not be able to keep up and would be blowing cold air. So I checked MX1 & MX2 and found 14 VDC. Warm and cool sensor and this voltage does not change. Disconnect MX1 and unit goes to high fire so this proved modulating valve is working properly.
Replace X-Trac2.1 Controller and now VDC will change at MX1& MX2 when discharge sensor is warmer or cooled.
Warm Discharge Sensor I had 13.1 VDC
Cold Discharge sensor I had 5.2 VDC