Command blocks create output when not powered

I tried to create a set of 3 command blocks connected to comparators so that the third command block would only activate if the first two were. But, the second command block would keep giving off a signal even if it wasn’t being powered.
Recreation:
1. Create a line of 3 command blocks spaced 1 block apart, then place 2 comparators between them.
2. Set the first command block to always active and repeating and the command to “testfor @p[r=3]”
3. Set the second command block to “clear @p diamond 0 0” with redstone required
4. Set the third command block to “say HELLO” with redstone required.

The commands are supposed to say HELLO if a player walks nearby with a diamond. However, even if the player moves 3 blocks away from the first command block, the second command block stays powered and won’t display the message again.