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It was about 90 degrees when I did it, probably around 8000 DA, it was on max blower. Just wanted to see in "normal conditions" what kinda ballpark of power loss we'd expect to see.
I don't plan on doing any more testing lol.
BTW the pcm has a table to model torque loss vs AC pressure, I've never logged AC pressure so I can't really speak to normal operating conditions for that. I believe it is an idle-specific table, so that the pcm can pre-emptively add airflow based on AC pressure so you don't get rev drop etc.
Ok, can we put to rest that the a/c does not draw 30 to 50 hp? It is much less.
The dyno pull is interesting but does not reflect the maximum a/c horsepower unless you were running the a/c at high blower, outside air, and an ambient representative of worst case where there are Corvettes. I think we have a forum member in Saudi Arabia so let’s say about 120 degrees F by 50% humidity. Let’s also remember that high side pressure typically reduces with road speed up to a point. In that Saudi Arabia ambient and bumper to bumper city traffic, your high side will be quite high. Well into the 300’s psi, possibly higher close to the 400 something high pressure cut out setting. If you were to run your dyno pull under those conditions, you would see a horsepower draw.
Now I’m not suggesting you do this, but if you wanted to see a closer representation of maximum hp difference, repeat your test but block off the condenser with a piece of cardboard (to drive the high side pressure up and keep it up as your vehicle speed increases) and then do your run. Of course you are likely to see your coolant temperature skyrocket too so not a good idea.
That's a good idea, but I think you'd still run into the issue of the ECM pulling timing due to the coolant temps.
I was off on my actual max horsepower estimate, but not on the fact that the engine doesn't make as much power with the AC running. Based on the OP's car being a stock auto, with what, a 1300 stall torque converter? Punching it at highway speed with the AC on loses about 20 ft/lbs of torque across the bottom half of the rpm band, so his observation about the car feeling sluggish with the AC on is valid. Aaron's observation about the compressor cutting off so no loss of peak hp is true as well, but the loss of torque BEFORE peak rpm is going to hurt acceleration, particularly off the line where it counts most, which is why we saw mostly stock cars lose time in the quarter.
The fact that the impala had a different engine may have caused a greater horsepower loss, too. The impalas ran iron heads, which are more prone to hot spots and pinging than aluminum.
But I'd still like to see what a stock-ish car would run back to back with the AC on and off.
Last I known a a/c to actuate at is @ or about 27 psi on the low and shut off @ or about 150 on the high side ... Your psi values are much to high ....
My a/c does not shut off @ WOT . Nice and cool @ 200
Last I known a a/c to actuate at is @ or about 27 psi on the low and shut off @ or about 150 on the high side ... Your psi values are much to high ....
I always thought the compressor shuts off under WOT condition?
The tables allow you to turn it off based on TPS or RPM. My C5Z tune it's set for shut off above ~4850 rpm, but the TPS part of it is disabled. You could easily change the setting to turn off AC above 80 TPS or whatever too, but I haven't bothered to change mine. There might be something related to AC pressure too, but I can't recall a table/value off hand.
The service manual has a nice table of pressure vs ambient air temp that I referenced when I recharged my system. IIRC mine was jumping around a lot when I tested it but that's probably most applicable here.
Quality sucks, but I found this real quick googling.
I looked around but I couldn't find the settings specific to the C5. All I was able to find was a generic R134a switch. 3.14 Mega Pascals = 455 psi. I'm pretty sure the C5 cutoff pressure is between 400 and 450 psi. I know it was 450 psi on the impalas.
