I have a 2008 Honda Odyssey. Lately the Climate Control panel fails to work intermittently: right after I start the car, none of the buttons on the climate control panel works(hence I can not turn on AC/FAN/DeFrost,etc), but usually after continuous driving for about 20-30 minutes, then I am able to press button on the climate control panel to turn on AC, etc, and magically all the buttons starts working perfectly. I suspected the car battery was too old and got it replaced with a brand-new one two days ago. On the 1st day after battery replacement, the climate control panel (all buttons) works great even right after car start, but on the 2nd day, the same issue happens again, buttons on the climate control panel works only after driving for 10+ minutes.

What could be the root cause?

 

Since brand new battery made it work, there might be some battery discharge happening that lowers the power in the battery. Suggest you take the van back to where you got the battery and have them check for its capacity to see if it is still fully charged or if there is a drain on the system.