cover the H21 when you switch the R15. start by programming code 00002 to av1 or av2 on the white remote like so:
1. av1 or av2
2. press and hold MUTE & SELECT for two blinks
3. enter 0 0 0 0 2
Slide back to directv device on the remote and enter the menu of the receiver:
1. menu> settings> setup> remote> receiver mode>
2. you will see either DIRECTV or AV1/AV2, click whichever to reveal both
3. choose AV1/AV2, the remote will stop controlling the receiver, slide to av1 or av2 on the remote, whichever has code 00002
4. press DONE and exit the menu