Strictly speaking, the gondola has no air conditioning. But that doesn't mean they can't air condition it beyond just "natural venting". I can think of 3 inexpensive ways:
1.The gondola opens its door and people walk in and sit down. Then the door will stay open a little further and reach the spot where a big tube points at near the top of the door and shoot out a blast of cold air (say, 55 degrees) that instantly replaces most of the air inside the gondola. The people inside screams and shudders from the sudden cold. The door immediately closes, keeping the cold air in, and the gondola is on its way. If the gondola is going from Pop to Epcot and bypassing CBR, the door will open at CBR station and another blast of cold air will take place.
2. The gondola can have water sprayed on it outside at intervals to keep it wet. The gondola is moving, so the rapid evaporation may remove a noticeable amount of heat.
3. The gondola can have a small compartment on top that fits a tray with a handle. The tray can hold a block of ice about 2 feet by 2 feet by half foot (about 4 gallons). When the gondola crosses a station, before it loads people, a robot arm can put out the old tray with half melted ice inside to be put back in the freezer, then shove in a new one. The gondola ceiling can be designed with vents to let the cold out while at the same time direct any condensed moisture outside.
The cooling methods only need to take place if the gondola temperature is over, say, 80 degrees.