Do DNC rules allow candidates to combine forces on the first ballot at the convention?

This would obviously only matter if no one obtains an outright majority during the primaries. My impression of the rules is that all delegates are expected to vote on the first ballot for the candidate they pledged themselves to during the primary process, that superdelegates (starting in 2020 as a new rule) are only allowed to weigh in on a second ballot if any, and that pledged delegates only become unbound starting on the third ballot. But I can’t find any clarification about the first part of this anywhere, including reading the rules. I also can’t find any support for the contrary. It’s a pretty important question, but everyone discussing these hypotheticals seems to be making assumptions without clear evidence.

DNC convention rules are are notoriously subject to change.

It depends on the state, but most, if not all, are obliged to vote for the candidate they are pledged to on the first ballot. After that, different states have different rules. The Votemaster had an item on that yesterday. Here it is in part:

Most states that put limitations on their delegates require them to vote for their pledged candidate. either for the first ballot where that candidate is in contention, or all ballots as long as that candidate is in contention. so if a candidae drops out of the race, they can release their delegates by NOT having their name placed in nomination. Since they are then not in contention, no delegates can vote for them. So the delegates can still vote for them 9and have their ballots count as ‘spoiled’) or vote for somebody else.

So it doesn’t matter if a candidate “directs” (or asks) his/her delegates to support another candidate? Let’s say Candidate A has 35% of the delegates, B has 30%, and C 25%. C would much rather see B as the nominee than A. She can’t throw her support to B and get him nominated on the first ballot?

If Candidate C has had her name placed in nomination, her delegates are required (by their state pledges) to vote for her on the first ballot.

If her name isn’t placed in nomination, then those delegates are free to vote for whomever they want. She can ask them to vote for candidate B, but each one can vote for whomever they want. (Presumably, since they were supporting her for President, they respect her judgement, so many or most of them will follow her advice and vote for candidate B.) But nothing legally forces them to do so.