AC - Does it really sap that much power?

[jameschong]

Does your c900 seem to sap significant power when the compressor is engaged?

I'm starting to turn the aircon compressor off when I want more power. This is not good.

I'm wondering if this is to be expected, or if it's a sign of something going wrong....

[grif900]

a.c. pump when engaged uses a lot of kw(hp). and c900s are not known for having much to spare, so the difference is very noticable. id say normal.

[900t]

At WOT it turns off...

Just imagine if you had an old 62 horsepower Benz 240 D with the super power sucking reciprocating-piston York A/C compressor

[grif900]

i used to have a 240 with a four speed manual trans.,we called it our luxury farm tractor and after i fixed the a.c. we just called it cool.but , driving it took planning,like when trying to pull out into a buisy roadway.or any other seemingly normal move.with the a.c. on i reckon it had about 7 weasel power.

[skilpadda]

I dont notice any difference in performance on my 91 900s when I run the ac. Only a slightly higher fuel consumption(8-10%).

[TheRedBaron]

Every car I've ever driven has performed worse with the AC on...unfortunately I can't comment on the c900 because I won't have AC on mine till the spring (for $280 including labor at the place I bought it from on stipulations of the selling contract!)

[woywitka]

yeah I notice it. If your running r-12 you shouldn't notice much, but since r134A takes tremendously more power to compress the gas it sucks LOTS of power.

[TheRedBaron]

Originally Posted by woywitka

it sucks LOTS of power.

Guess when I get my AC done I'll have to mod my car s'more to make up for it!!

[woywitka]

Originally Posted by TheRedBaron

Guess when I get my AC done I'll have to mod my car s'more to make up for it!!

won't help, it is off the line that is sucks, once boost hits or i'm on the freeway I don't notice it much.

[Jim Mesthene]

Jaguar XJ6 A/C systems were 36,000 BTU.
Assuming the SAAB's is smaller, say 25,000 BTU, you can expect it to use abot 10kw (15 horsepower?) at full load. That's why there's a full throttle switch that turns the compressor off when the throttle is wide open.
So, the answer is: yes, it uses a lot of power; no, it doesn't slow you down.

[woywitka]

Well the other issue with the Saab system is that it was designed to run r-12, and I'm told it is brilliant with r-12; however, r-12 burns holes in our ozone and we must run r134a. R134A operates at much higher pressures and takes twice as much energy (or more) to produce a fraction of the cooling ability of r12. That is why our A/C sucks with r134A, it is "cool" but not "freezing".

The power loss with r-12 I was told by older Saabnuts was barely detectable, and when the compressor cut in when you were relasing the clutch it wouldn't screw you up.

[cdaly]

Originally Posted by jameschong

I'm starting to turn the aircon compressor off when I want more power. This is not good.

I'm wondering if this is to be expected, or if it's a sign of something going wrong....

I wonder is your Throttle Position Switch not working? There should be a pair of contacts that are shorted when at WOT and open otherwise.

[Jim Mesthene]

Originally Posted by woywitka

Well the other issue with the Saab system is that it was designed to run r-12, and I'm told it is brilliant with r-12; however, r-12 burns holes in our ozone and we must run r134a. R134A operates at much higher pressures and takes twice as much energy (or more) to produce a fraction of the cooling ability of r12. That is why our A/C sucks with r134A, it is "cool" but not "freezing".

The power loss with r-12 I was told by older Saabnuts was barely detectable, and when the compressor cut in when you were relasing the clutch it wouldn't screw you up.

I'm not a SAAB nut, but I'd worked on R12 systems for 20+ years before R 134a came along. 900s always had weak A/C, not brilliant.
Pressures are only a little higher with134a. With a larger condenser, performance is about the same, with the old condenser retrofitted with 134a, you need more airflow; pressure can rise in traffic.
I never noticed any difference in power loss (although, theoretically there should be some).
In traffic 134a is lame instead of barely adequate, at speed, there's not much practical difference.

[900t]

If you think R134a sucks, wait until R134a is banned, as the EU is doing in 2011... global warming...

They want to use CO2 as a refrigerant, but it takes like 5x the pressure of R134a

[GearHead]

what about propane?

[900t]

It's great but for some reason people don't like to put 500 grams of propane in their car, even though there is 50 kg + of gasoline in there too Apparently window-mount air conditioners for homes in Europe are going to start using propane though which is surprising. I guess the Europeans like to live a bit more dangerously than us North Americans.

[jameschong]

I'm still allowed to use R-12 in Singapore, since the car was registered before legislation banning R-12 came into force.

The TPS, temperature and pressure sensors work to cut the compressor off and restore power. But it's non-WOT conditions that make the power loss bad. As well as vibration and a drone which I think it from the belt under tension.

The compressor itself works well, delivering the pressure (I just had it checked recently). But the location of the evaporator, on the "hot" (or right) side of the engine bay doesn't help.

The AC cools the car marvellously when it's going at highway speeds and the engine isn't hot. When it's in stop/start traffic, it barely cools.

And it doesn't help with the black fabric roof under the mid-day sun in the tropics....

[cdaly]

If there was not enough gas in the circuit, you wouldn't get good cooling except at high engine revs. Is there a sight glass on top of the receiver? If so, you should see bubbles in this just after the compressor cuts in and they should clear away after a few seconds. If they persist or only go away under high revs, you're most likely low on gas.