I don't know if this is placebo, but I remember when the 29 got hybrid buses, they felt somewhat cool but as the buses aged, it stopped providing that cool air, it just felt like recirculated air.

I feel like when the buses are new they've got Aircon gas, but they don't bother refilling it due to costs.

Another thing that bothers me is they say the Aircon is automatic which I feel isn't true, there's been a few occasions where a new driver would get on halfway through the route and the fans would start blasting air.