Check fuse no.12 (7.5 Amp) in the under-hood fuse/relay box.
Check fuse no.30 (7.5 Amp) in the driver's under-dash fuse/relay box.
If both are fine, you have two options:
a) Perform a self-diagnostic function using the climate control unit
b) Have your Honda dealer plug the HDS computer into your truck in order to retrieve any fault codes that have been logged
Self-Diag function (Ridgeline RT/RTS)
1) Turn ignition switch off
2) Set fan control dial (left knob) to off and temp control dial (right knob) to MAX cool
3) Turn ignition switch on (position 2) and select any vent mode (choice of four flap positions for air direction)
4) While pressing & holding
the A/C button, press the recirculation button (directly below the A/C button) a total of five times within ten
seconds. Release the A/C button as the recirculation indicator (lamp on the recirculation button) will blink two times and then commence the self-diagnostic
5) If any faults are found, the recirculation indicator will blink once or numerous times which indicates a fault and a required trip to the Honda dealer for subsequent estimate and repair
6) To restore system, turn ignition switch off
Hope this helps!