Having A/C on vs power

[Stkid93]

Hey guys,

I’m going to split this post into 2 parts but both will talk about having the a/c on in regards to power.

part 1)

I just watched a video in which a guy dynoed a v8 Lexus with the a/c on, and off. The results were pretty amazing. The car lost about 40 ft lbs throughout the entire rev range, and about 15-20 horsepower throughout as well. It ended up being about 12-13% reduction in torque and 9-10% reduction in power.

I realize this is an incredibly specific test and a long shot, but Has anyone ever dynoed their fist with a/c on and off? Even a virtual Dyno would be fine? Now that I saw this video I think I’m going to do my own virtual Dyno with the ac test asap.

What do you guys think our results would be? Now I have heard, the smaller the engine the more these parasitic parts will drain power. Example, a large v8 won’t really be affected while a small 4 cylinder will lose a ton of power. But obviously this video proved that at least some what incorrect.

part 2)

I also read that some of the newer cars automatically disengage the a/c compressor when going wide open throttle even if the a/c is on. However I don’t think this is true for the fists? Does anyone know for sure? If this were true, the a/c inside the cabin would shut off when going wide open throttle, I know most of us will have the a/c off when driving hard but sometimes it’s so hot you can’t avoid it. and while I’ve never really paid attention to my a/c during wot pulls, I’ve never really noticed the a/c go off either.

with some other model cars I’ve heard some people say their owners manual says it disconnects above 80% throttle. I assume each manufacturer is slightly different.

So to recap.

anyone have a Dyno or Vdyno comparing a/c on or off?
What do you think our power loss would be considering it’s turbo and a tiny engine?
Does anyone know if our a/c compressor disengages automatically at a certain throttle input?

 

[Capri to ST]

Hey guys,
Does anyone know if our a/c compressor disengages automatically at a certain throttle input?

I am under the impression that our AC compressor disengages at full throttle, but I can't find an authoritative source for that.
I assume the fan would stay on, and just the compressor would disengage, therefore there would still be some residual cold air blowing out of the vents for some period of time, probably longer than the period of time that you could go full throttle.

 

[WannabeST]

I have an obd2 gauge that shows the load on the engine.
Keep in mind everything I'm saying is from a fiesta SE. Not sure if ST is better/worse or completely different but just want to share my findings, hopefully it helps a tad.
On my obd2 gauge at idle the car is at roughly 15% load. If I turn AC on at idle the load goes from 35-40% It seems to work harder when it's hot out (no surprise) but I don't see that much variance in regular no ac idle.
If I'm cruising on the freeway the load is basically always roughly 20% more than normal at whatever rpm and/or mph I am at. I can go full throttle on my car and AC stays on. I've accidentally left AC on before on track and it killed my speed out of corners and on straight away, I usually didn't realize till after my sessions. ( I would keep AC on in the pits then turn off when track went hot, but I'm dumb and forget sometimes)
I can't confirm the horsepower or % loss on my car. However, if it helps your research I can do some pulls with and without ac on and report the results.

 

[Stkid93]

@WannabeST @Capri to ST

thanks for the replies guys, whatever you have to report back on keep it coming, if you guys also want to do virtual vdyno testing to compare and post here that would be awesome, I would assume the power loss would be similar for the se. only big difference being the turbo, so the ST may lose a little more power with the a/c who really knows

also, Capri to ST have you ever owned a mercury capri? I’m just judging by your username. My father runs a company in which he specializes in mercury capri parts. He also has extensive relations with ford dealers and has helped me out with parts in the past. He’s probably spent millions of dollars with ford over the years.

 

[Alkoran]

This should answer the question:

 

[Capri to ST]

@WannabeST @Capri to ST
also, Capri to ST have you ever owned a mercury capri? I’m just judging by your username. My father runs a company in which he specializes in mercury capri parts. He also has extensive relations with ford dealers and has helped me out with parts in the past. He’s probably spent millions of dollars with ford over the years.

Yes I have owned a Mercury Capri, you correctly figured out the reason for my forum name. As a young car fanatic back in the day, I talked to my dad into getting a 72 Capri 2000. We loved that car, shared it back and forth through the years, and had many great times with it. For me, it was the start of a lifetime of being interested in cars. When I got the Fiesta ST, I felt like in some ways I was coming full circle, because they were both quick and agile Ford performance cars of European origin .

 

[Capri to ST]

This should answer the question:
View attachment 59686

That does answer it, good find.
If I overthink it enough though, which is my specialty, it makes me wonder if the A/C is already on and you then go full throttle, will it shut off?
Because on its face it says the A/C will not come on if you are full throttle at the time that you try to turn it on.

 

[Stkid93]

Ok so if you are wide open, it appears to shut off. However, if you are at part throttle or even 95% throttle. The a/c would still be on. I am really curious to see some numbers. Assuming our car is similar to the Lexus i saw. We are talking about 15-20 horsepower and 40 ish torque.

I don’t want to turn this into a e30 vs 93 thread. But like the difference between 93 and e30 (on stock turbo) and for me I notice a huge difference. I just had to go back to my 93 tune for a few days after being exclusively e30 for almost a year. And wow does the car feel like a dog, it’s like I have taken e30 for granted cause I got so used to having it always. And every time I go back to 93 I get reminded of the difference like a smack in the face lol.

 

[WannabeST]

I think the best way to do this would be to put a go pro with a light in your engine bay and have an obd2 gauge reading throttle input

 

[Alkoran]

I think the best way to do this would be to put a go pro with a light in your engine bay and have an obd2 gauge reading throttle input

Or just take the OBD2 scanner on live data with both the AC control PID and throttle % PID. I don't think the gopro is necessary

 

[Intuit]

I also read that some of the newer cars automatically disengage the a/c compressor when going wide open throttle even if the a/c is on.

Even my '94 vehicle cut the compressor with WOT. IIRC that generation of vehicle started with 1990. Manufacturers probably saw fit to do this way back when they started building EFI 4 cylinder engines for the mainstream passenger vehicle. (versus just the stripped down basic economy vehicle)

 

[scooter123]

In 1985 I purchased a Chevrolet Monte Carlo SS. With that car the AC compressor would shut off at anything over 3/4 throttle. Still have the SS only now it's powered by a GMPP HT383 and the Air Conditioning has been stored in a box since 1994 because the compressor froze up from not being used. Because I am one of those freaks of Nature who believes in Acclimatization. As a result I keep the thermostat in the summer set to 80 degrees and only use the AC in the car for about 2 hours a month to keep the seals in good condition. I'll also go out for a run when it's 100 degrees, it works great for getting every muscle super loose and I feel really great after a "hot" run.

So, for the FiST I expect that it does shut off the AC when there is a demand for high power. it's not a new scheme and I expect that all of the Big 3 started doing this in the 60's or 70's. Because those older compressors were real power hogs. I was once told that those old Chrysler compressors could soak up as much as 50 HP and I know for a fact that my Dad's 71 300 with it's 440 Magnum could frost the dash vents solid when it was humid enough.