AC air vent block issue!!!

[PlunkZ71]

Long trips makes sense. Air doesn't have *that* much moisture in it and it'll take a bit to plug it up with ice such that you notice airflow problems.

Under what conditions were you measuring those pressures? Fan speed, ambient temp, RPM, vent temps (use a meat thermometer not infrared) and whether or not you're experiencing the icing issue

Pressure was measured at 98 degrees ambient temp at idle. Didn't have a thermometer in the vent. Did Not note the fan speed or RPM

 

[SnowDrifter]

Might be worth your time to check again, ideally with the freezing issue replicated. Unfortunately, in this case, a single data point doesn't say much