Since it's United, I say you are out of luck. Their customer service is the worst and last summer I overheard them tell a woman that "United doesn't care."
I have also been on plane where the AC didn't work. And the refreshment du jour was a bottle of room temperature water. An older woman passed out. They did find a cold bottle of water for her.
Trust me - they don't care! As the steward said - just be glad your plane is leaving!
I will only fly UAL again if there is a major illness or death in the family and it's the only way home.