We know the Halacha says, according to Maran, that Kohanim must wash their hands Netilat Yadayim without a Beracha before they make Birkat Kohanim. They have to do this even though they made Netilat Yadayim already earlier in the morning. Although that was not the opinion of Rambam, but we said Maran was Machmir (strict) in this case that Kohanim still need to wash. The question asked is, are Kohanim required to wash again for Birkat Kohanim in Musaf if they washed already for Birkat Kohanim in Shacharit?
So according to the letter of the law, so long as the Kohen knows that he was careful that he didn’t touch anything that would require another Neitla, he then may rely on the washing that was done for Birkat Kohanim in Shacharit. Things that would require another washing would include; sticking one’s fingers in one’s ears, scratching your head, touching shoes, etc. As long as the Kohen was careful not to do one of those things since his last wash, so according to the Halacha, he does not have to make Netilat Yadayim again. And that is also the opinion of Chacham David Yoseph in Halacha Berura, volume 6, page 359.
However, those who are Machmir (strict to do it better), upon them will come blessings. There are some opinions that say the Kohen must make Netilat Yadayim close to the Birkat Kohanim. They say that the washing made for Shacharit is to far away from Musaf. But again, from the letter of the law, if the Kohen washed for Shacharit and he was careful, he would not have to wash again in Musaf. But for those who want to be extra Machmir and wash again, upon them will come blessings. That’s the opinion of Tosafot, and Magen Avraham, and others.
Another Halacha should be pointed out. Once the Kohanim wash their hands, whether it is in Shacharit or in Musaf, they should not talk until at least Birkat Kohanim is over. Some of the Kohanim might come to talk while in the hallway on the way back from washing. They should not talk once they make Netilat Yadayim. Talking for everyone is in fact prohibited at that point, so Kohanim must be careful and refrain from talking.
