HP rating and AC

[schnellfahrer]

Here are a couple of questions I´ve been pondering.
Hope someone can answer these.

How much HP does it take to run the AC?
Is there any parasitic loss when the AC is turned off?
Would you have to remove the belt for there to be no loss whatsoever?
Is the factory HP rating with or without the AC running/connected?

tia

Eivind

[DanielDudley]

AC can eat 2-4 HP IIRC. In England the 928 boys think that disconnecting the AC and the smog pump is a big power secret. I don't think you would notice the difference with the AC off.

[spuggy]

Originally Posted by schnellfahrer

How much HP does it take to run the AC?

A fair bit, I think. My NA 944 would run as much as 2-3 temperature bars higher (50% or 75% instead of 25%) with the A/C on. And felt noticeably more sluggish @ WOT.

Ironically, more than once I turned it off in hot weather because I was concerned about the engine temp.

Is there any parasitic loss when the AC is turned off?

Very little, because the electric clutch isolates the compressor so you just have a belt and pulley with no load on it.

You still have the additional weight of the compressor, evaporators, fans, refrigerant etc. to drag around

Would you have to remove the belt for there to be no loss whatsoever?

I'd be more concerned about the weight of the compressor, radiators, coolers, evaporators etc. if I were you. I think that would be far more noticeable than the negligible drag from the belt.

Is the factory HP rating with or without the AC running/connected?

I remember reading somewhere that quoted factory HP ratings are (a) conservative and (b) measured with all normal ancillaries (oil pumps, water pumps etc.) fitted. Apparently some manufacturers arrive at their power ratings with external oil and water pumps and no alternator...

That said, the power would definitely not be measured with the A/C running. And I wouldn't expect an optional item like AC (which wasn't standard fitment AFAIK) to be fitted to a motor used for a power rating.

[dentist90]

Originally Posted by spuggy

with the A/C on.... felt noticeably more sluggish @ WOT.

Interesting observation. In the Motronic cars (84's and onward , can't comment about older cars) the WOT switch deactivates the A/C clutch automatically. I am in the habit of turning off my A/C momentarily when I am planning to pass regardless.

But you're right, the A/C does cause the engine to run warmer... for a couple of reasons. One is that it is placing a drag on the motor of some 3-5 HP. On air-cooled cars the more direct reason is that the largest condenser in the system is located in the stream of cooling air for the engine. This has the effect of raising the cooling air temp by several degrees.

As I don't race my car I invested several hours of work and hundreds of dollars to get my A/C working so that I can cruise for hours without cooking my own command module (ie, my brain!)

[schnellfahrer]

Great info!

Thanks!

[spuggy]

Originally Posted by dentist90

Interesting observation. In the Motronic cars (84's and onward , can't comment about older cars) the WOT switch deactivates the A/C clutch automatically.

Interesting, I did not know that. It might simply have been that it felt slower on part-throttle - but it's long-gone anyway.

Originally Posted by dentist90

As I don't race my car I invested several hours of work and hundreds of dollars to get my A/C working so that I can cruise for hours without cooking my own command module (ie, my brain!)

Heh. My PO thoughtfully saved me a lot of aggravation by removing all traces of the A/C from my car before I bought it.

I find the opening rear windows are surprisingly effective once you're moving...

[dtxscott]

The irony is that a guy from Norway being concerned about aircon.

Good luck in your search.

[schnellfahrer]

Originally Posted by dtxscott

the irony is that a guy from norway being concerned about aircon.

good luck in your search.

:d