You are correct (and I never said) "the compressor uses more power to cool hotter air".......The system does how ever need to be sized to take into account it's working environment and performance expectations (pulling the cars interior down from 60+ degrees to around 20 deg or less and maintain it).
Ambient temperature absolutely plays a part in automotive a/c..... A condenser doesn't reject heat at a constant rate regardless of ambient temperature and / or airflow, does it?........It's basic physics.
Your trying to tell me that your bench demo a/c was a 20,000 btu set up running on 1.5 hp?.......Sorry, but I don't think so.
Do you honestly think a 1.5 hp system will cool your car on a 35 degree day?
The rated belt loadings you mention are interesting, seeing as the commode super charger / auxiliary drive belt (8pk) on the supercharged v6 delivers 30-40 kw to drive the factory eaton supercharger when it's producing only 8-9 psi (and up to 70kw when the supercharger is overdriven to produce 10 - 12 psi).........Plus the same single belt also drives the a/c, water pump, power steering & alternator.
Me a mechanic?......I can't even change oil.....
In regard to BTU = watts
20,000 BTU per hour = 5.858 Kw (7.855 Hp) @ an unrealistic 100% efficiency.