Odd Fact of the Day

"CAcoalminer" (CAcoalminer)
07/24/2015 at 14:30 • Filed to: None

All of the test cars have air conditioning, but that shuts off at full throttle with a six-second reset.

I’m confused by this fact. Is the Viper ACR’s air conditioning system such a power drain that it is truly beneficial to shut it off? For me personally, this feature would prove quite annoying. If I have the A/C on, then I want it to stay on all the time regardless of whether I lose a few hp.

Do any of you know of other vehicles that have a similar feature like this?

Source of images

DISCUSSION (32)

Nerd-Vol > CAcoalminer
07/24/2015 at 14:33

I'm pretty certain my Speed 3 does that.

MIATAAAA > CAcoalminer
07/24/2015 at 14:33

All of my cars do this. But it doesn’t depend on throttle position, it depends on RPM. My Matrix turns the AC off above 6,200RPM. Not sure exactly when it happens with the BMW and Miata.

Smallbear wants a modern Syclone, local Maple Leafs spammer > CAcoalminer
07/24/2015 at 14:35

If I have a vehicle with X hp at full throttle, I expect it to give me X hp at full throttle, even if it shuts the AC off. You aren’t going to be flat out long enough to notice anyway.

Many vehicles have this feature. I can’t name them all, but if an ‘06 Malibu SS had it...

RamblinRover Luxury-Yacht > CAcoalminer
07/24/2015 at 14:37

Power drain? No. A/C is a heat load and cooling system effectiveness drain like a mofo, though. Cooling systems tend to be really marginal in high throttle use in terms of what heat they can actually remove for given airflow, and A/C can be the anvil that breaks the camel’s back.

TractorPillow > Nerd-Vol
07/24/2015 at 14:38

I had a 2010 and never noticed that. Maybe a little less blowing, but not shut off

gometz > CAcoalminer
07/24/2015 at 14:38

My co-worker shut off the A/C in his 2013 Mustang GT when he was showing me the acceleration. First time I ever saw that, but he’s more into drag racing.

TractorPillow > CAcoalminer
07/24/2015 at 14:38

Yes. My 02 viper. But i don't think it's a 6 second exact shut off.

Michael > CAcoalminer
07/24/2015 at 14:39

S13 240SX’s cut the a/c on full throttle.

MPA > MIATAAAA
07/24/2015 at 14:40

Same here - every recent car I’ve owned did that. My Hundai Accent shuts off after 2-3 seconds of full throttle. Since it’s hot I usually lift so I don’t get warm :D

deekster_caddy > CAcoalminer
07/24/2015 at 14:50

I’m pretty sure modern vehicles do. I used to do this manually when going up long hills. They all should!

CAcoalminer > deekster_caddy
07/24/2015 at 14:52

Interesting.

CAcoalminer > MIATAAAA
07/24/2015 at 14:53

Maybe I just haven’t been paying attention.

CAcoalminer > Nerd-Vol
07/24/2015 at 14:53

Interesting.

CAcoalminer > RamblinRover Luxury-Yacht
07/24/2015 at 14:55

It seems odd that someone couldn’t engineer a solution for this.

deekster_caddy > CAcoalminer
07/24/2015 at 14:55

Modern A/C systems tend to cycle the compressor on and off anyhow, and just go for a target pressure - so most of the time they can handle a few seconds off without the air temp changing at all. It takes more time than a few seconds for the evaporator to “lose it’s cool”...

CAcoalminer > Smallbear wants a modern Syclone, local Maple Leafs spammer
07/24/2015 at 14:55

I was just assuming that’s why they turn it off. I’m not certain at all.

CAcoalminer > gometz
07/24/2015 at 14:58

That makes sense, as I have heard of individuals who drag race or track heavily doing that. I was just confused as to why they would engineer the car to do it by itself. In my mind, if you don’t want the A/C on just turn it off.

CAcoalminer > TractorPillow
07/24/2015 at 14:58

Interesting. How did you like your Viper?

CAcoalminer > deekster_caddy
07/24/2015 at 15:00

Thank you for the thorough explanation. This has truly been enlightening.

CAcoalminer > Michael
07/24/2015 at 15:05

Hmm

TractorPillow > CAcoalminer
07/24/2015 at 15:22

I just got it 3 months ago and love it. I bring changes of shirts when I drive because AC is not its strong point and the exhaust goes under the side sills resulting in a hot cabin when accelerating. but I compromise a lot for cars that kick ass to drive.

Jake - Has Bad Luck So You Don't Have To > CAcoalminer
07/24/2015 at 15:22

My Civic doesn’t do this and I wish it did. The A/C is an insane drain on my car’s ability to move foward.

RamblinRover Luxury-Yacht > CAcoalminer
07/24/2015 at 15:25

The “solution” is to make the front of the car so big and the airflow so massive that the car sounds like a jet and takes serious aero-related hits to fuel economy over 30 mph. From the stylist’s point of view, the cooling intake must look good. From the safety engineer’s point of view, the inlet must not interfere with bumper design or pedestrian safety, and from the aerodynamicist’s point of view, it must not take in more air than absolutely necesssary, and where it takes it in is in question, because discharge and uptake locations must correspond to desired reduction and increase in pressure. The nose is a good place to reduce... to a point, but the underside of the car is not necessarily a good place to dump, and the air is hard to move through the nose enough that it’s hard to do much with air that wouldn’t be easier just slipping through and reducing profile.

The thermal enginer MUST compromise, in airflow, noise, sizing, coolant flow, coolant/air thermal difference, and many other things. If he compromises for proper cooling at 30% throttle moving slowly, then 60% throttle moving 2.5 times as fast may work fine- as long as outdoor temps don’t start climbing. The amount of air available at a given speed *from the car pushing through it* is linear. The heat needing to be dumped isn’t - it increases faster. When the car is operating at full throttle, it usually is struggling to be able to cool itself, and a lot of the system is building up heat to a point - if you then slow down, you have a system with a lot of heat still remaining in storage, in the block, coolant mass, oil, and elsewhere, that is no longer receiving enough air to help remove it. BLAM, temperature spike. Banning the A/C from adding any extra heat while the system’s building heat is just good practice - it means less of that heat hangover.

CAcoalminer > TractorPillow
07/24/2015 at 15:53

That’s terrific to hear. Have you done any modifications to it or have any planned for the future?

CAcoalminer > Jake - Has Bad Luck So You Don't Have To
07/24/2015 at 16:00

Couldn’t you just turn it off yourself?

CAcoalminer > RamblinRover Luxury-Yacht
07/24/2015 at 16:02

Wow. Thank you for that terrific explanation.

TractorPillow > CAcoalminer
07/24/2015 at 16:08

No, I don’t like modding my cars. I also have car ADD so don’t keep them more than a couple years so not worth the investment. I know 450 hp sounds tame these days, but it’s more than enough for me. I just put new r888s on it and that made a huge difference.

I cross shopped a MB gla250, outback and Viper. 10 year old me won the battle.

Jake - Has Bad Luck So You Don't Have To > CAcoalminer
07/24/2015 at 16:21

Yes, but the button for the compressor is on the passenger side of the center console, making it the farthest button from the driver that exists in the car. I’m far too busy with important matters like passing Richard Burns, heel-toeing, eating a cheeseburger, and receiving sexual favors to be bothered with such plebian concerns such as turning off my A/C compressor so I can maintain my speed up a hill.

CAcoalminer > TractorPillow
07/24/2015 at 18:47

No, 450 hp doesn’t sound tame at all. I think people sometimes undervalue how powerful anything about 400 hp truly is.

Interesting choices. I think you made the right one.

CAcoalminer > Jake - Has Bad Luck So You Don't Have To
07/24/2015 at 18:48

Ah, I see.

MIATAAAA > CAcoalminer
07/25/2015 at 03:24

Perhaps you live in a place like San Diego and you don’t really notice when the A/C cuts out? Perhaps.

CAcoalminer > MIATAAAA
07/25/2015 at 19:18

I actually live in Dallas so it seems like I would have noticed.