Do I have to drain the antifreeze in order to replace the ect sensor and the t-stat?

Just drain enough so the coolant is below the sensor and Stat-your decision

Agree ;)

Also check the windshield for leaks. Remove both A-Pillars in the front and go to a car wash with a high pressure hose if you do not have one. Have someone spray around the windshield area and check for leaks. If it is leaking have the windshield resealed. If that is ok remove the front passenger carpet. Look under dash for the climate box and towards the right side of the center console you should see the A/C drain grommet. Remove it and inspect for debri and clean out. Attaching some pictures also. First 2 is some places to look for the windshield leak. The glass was removed to see where it could drip from. The third is the drain grommet you need to inspect and the fourth pic is where you should see the water drain from when the A/C is on. Good luck to you and let us know what you find.