Hi experts

I have a 1999 s70, and no power to the climate control unit. I checked the fuses and pulled the radio and reached around to the back of the climate con unit and tested for loose connections. I checked the cabin air temp sensor for clogs and gently blew some canned air near the grid. I checked other posts but my issue seems a bit different(?)

The problem began with erratic operation (power on power off) - I thought it was shorting with rainy weather but now it’s continuous irregardless of the weather.

What would the diagnostic procedure be to narrow down the issues? I’d like to make sure it’s the unit itself before replacing parts Willy niilly. I have an electrical meter but hesitate to test contacts on the back of the unit without knowing which contact I should be checking for power.

Any thoughts and ideas welcomed!