Subject: Re: [s-cars] A/C

[Wayne Dohnal]

I'll dust off the rusty engineering skills and take a crack at answering why
the A/C is run off of a belt.  I've heard that the A/C takes about 5 HP from
the engine.  Starting with this assumption, that means an electric motor
would need 3730 watts, which at 14 volts is about 266 amps.  But since the
motor won't be 100% efficient, it would draw over 300 amps.  IF we had an
alternator that could handle this draw, it would just transfer the drain on
the engine from the A/C pulley to the alternator pulley, but require more
engine power because of the losses in the alternator and wiring.  To counter
this, the system could use a hermetically sealed compressor like most
electrically-driven refrigeration units, which would give us a huge increase
in reliability and I'd assume a more efficient system.  A car A/C system is
considerably more powerful than a typical window A/C because of the
tremendous amount of solar heating through the windows.

Wayne Dohnal
1994 S4


<parts of post snipped>
>My next question is that since our compressors
>are so ancient and will probably need to be replaced
>anyway, has anyone come up with a solution that is
>less power draining than having it run off a belt?  I
>was thinking of an electrical source rather than a
>pulley, being drawn from the alternator?  Just a bit
>of curiosity here and frustration at losing some
>performance when at WOT on hot days...which I probably
>shouldn't do before I load up on a nice big
>intercooler, anyway.  Anyone BTDT?  There is the space
>in our bay, but can it be done?