What load capacity should a ladder have for A/Cs?

Here's a longshot. Go to a local heating and air conditioning shop and see if they would be willing to lend you a duct lift like in the #3 post. A duct lift would be the safest way to get the units up and down. Call a couple rental places to see if they have them. I know it's more expense but it's better than getting hurt or dropping it.