80% chance it's a vacuum supply hose to the HVAC control.......with no vacuum they system defaults to defrost because the actuator is spring loaded to that side.

 

Thanks guys.

Looks like I was here before. I recognize my brand of ethnic engineering. Shrink tubing and a tie-wrap.




The thin tube just drys out and breaks. This time I used aquarium air hose and some RTV. Old dog, old tricks.