Quote:
Originally Posted by phil1968
The A/C compressor saps about 5 hp, about the same as the power steering pump & alternator combined. If you think about it, the engine is only generating probably twice that at idle, so no wonder the rpm drops when the A/C is turned on. The most recently used refrigerants (R134a & R1234yf) do not deplete the ozone, they do however contribute to greenhouse gas production. The previously used refrigerant, R12, was used up until the early 90s & that did contribute to ozone depletion. "Freon" is a trade name BTW, the same way you'd call a vacuum cleaner a "Hoover" or "Sellotape" sticky tape.
Going slightly off-topic, I work as a contractor for a large pub chain & their policy is to open all external doors in the pub when the outside temperature goes above 21 deg. C with the aircon going flat out. Go figure  |
Whoever sets the policy for that pub chain needs to sober up, stop drinking the pub chains products and smell the coffee and change the policy!
Just to expand on the alternator consumption, the alternator in mine is 120A @ 14V = 1680W if all of its output is being used. As most wound components are about 80% efficient, that means it uses about 2100W to drive it or just under 3hp. One horsepower is approximately 750W (actual figure is near 746 but i can't remember it off the top of my head) to give an idea of the conversion.
However, both the alternator and PAS pump only present load to the engine if they are being used - the laternator will almost always be providing some charge, even if only a few Amps to cover the basics. The PAS pump will freewheel until it's called on to move the steering though.
The big difference is most of the cars we talk about on here have Constant Displacement compressors. This means they are either on or off, much like your fridge at home. Later cars from the late 90s on generally have Variable Displacement compressors which only work as much as is needed to bring the temperature down to the level needed so aren't shuttling on/off like the older Constant Displacement variety.
With the compressors we have, they will be felt to "kick in" and as pointed out above, the engine is not making much more than what the compressor needs in terms of power with the minimal fueling for a clean idle.