Driving style in hot weather with air conditioner ON

P

peter.sellers

Member
:
MS3
I think my MS3 is very unhappy with the air conditioner on in this insanely warm weather. So, I have been taking it easy on my driving style and shifting at lower rpms - around 3K.

It almost feels like my car is getting bogged down when the temps cross 96 with the air conditioner turned on.

What driving style are you guys adopting?
Anybody gunning it in this warm weather?
Any safeguards to driving in hot weather?

Thanks
 
"Gunning it" will only cause the ECU to turn off the A/C. Very much of that, and it'll get unbearable inside the car.

No engine likes heat soak. You're bound to put out a few less HP with warmer air going into the engine. This is part of the reason I don't like TMICs...they get hot, and stay that way.

My Kia is programmed to shift up through the gears ASAP, loping around in 6th gear at 42mph. So I put it in manual mode and keep the RPMs between 2000 & 3000 rpms anytime that I'm moving. Below 1500 rpms, most A/C compressors are putting out less pressure, which amounts to less cooling in the cabin. When sitting at long stoplights, I put it in neutral and hold the revs around 2000. You can definitely tell the difference between 2000 rpm and 750 rpm where the A/C is concerned.

Really no safeguards to mention beyond keeping your eye on the temp guage and checking the coolant level periodically. Temp guages are buffered so heavily that it's not likely to show any hotter than it does in the dead of winter, so if it does move to the hot side, pull over and shut down ASAP.
 
I was winding it up a bit at traffic lights to help the compressor, but that was killing my mileage, so I quit doing that. I just drive normal - no short-shifting. It was 103 when I left work today (heat index around 115, probably). It was fairly comfortable after ten minutes or so. According to my scan-gauge, the water temp was 'bout 105 when I started for home. It got to 186ish and settled there.
 
I have noticed in high heat that my car would bog when the red light turns green If I try to blast away quickly from the light. I switch my style to a smooth driving style and there is no problem. By that I mean a linear application of the throttle. I've had other cars do this with the AC on in high temps so I wouldnt consider it a problem per say. I use a Cobb SRI and it sucking in very hot air MIGHT have something to do with it.
 
no extra safeguards needed. the ac will cycle in and out as needed to satisfy whatever temperature you have set inside the cabin. aside from that it's a matter of dealing with the power loss under normal driving during those moments the compressor is working

i have the gt so i always end up using the auto function and leave it around 74. only issue i have is that sometimes i don't realize when the compressor is running so my shifts aren't so smooth. when that thing runs and you go to change gears its like having a lightweight flywheel

although i don't normally drive in a "performance mode", i certainly don't expect anymore performance when using the ac
 
peter.sellers said:
Cobb SRI & Forge BPV. Everything else is stock.
Click to expand...

No need to drive differently. You will be down on horsepower in the summer heat. For every 10 degrees of increased intake temperature you lose 1% of your horsepower. So, comparing 60-70 degree spring weather to 100 degree summer temps is 30-40 degree swing. That's as much as 4% power loss. Doesn't sound like much? .04 x 263 = 10.5 horses loss. And then you add the effect of heat soak. Temps under the hood may be 140 and you're running an SRI which will draw that temp air until you get moving and pull some 100 degree air through the grill.

No reason to drive differently, however. Just know that power will be down.
 
oaklandopen said:
... i have the gt so i always end up using the auto function and leave it around 74...
Click to expand...
Man, here in the Florida swamps, I never set mine that high. When I leave work, I set it on 60 and rarely set it above 70.
 
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I just leave it at a constant 69 or 70, any higher or lower just aint comfortable. I'm guessing it gets very humid in florida, so A/C would be a must.
 
Oh, yeah. Lately we've been in the upper 90s with matching humidity. You may have heard the term "Air you can wear". That's us. I have to run my wipers going to work to keep the fog off the windshield due to the air being on.
 
o_O My car was fine that 1st hot streak we had coming back from Myrtle through SC, NC, VA and MD when it reached 104. I had the AC on the whole way. It was fine. If it's really hot I'll watch my IAT's and if it's too warm then I won't beat on it.
 
MSMS3 said:
No need to drive differently. You will be down on horsepower in the summer heat. For every 10 degrees of increased intake temperature you lose 1% of your horsepower. So, comparing 60-70 degree spring weather to 100 degree summer temps is 30-40 degree swing. That's as much as 4% power loss. Doesn't sound like much? .04 x 263 = 10.5 horses loss. And then you add the effect of heat soak. Temps under the hood may be 140 and you're running an SRI which will draw that temp air until you get moving and pull some 100 degree air through the grill.

No reason to drive differently, however. Just know that power will be down.
Click to expand...

+1
 
MikeHTally said:
Oh, yeah. Lately we've been in the upper 90s with matching humidity. You may have heard the term "Air you can wear". That's us. I have to run my wipers going to work to keep the fog off the windshield due to the air being on.
Click to expand...
+1 on the condensation/wiper package
I just might pick up some rainX and give it a try

71 on auto here in tampa is a decent setting
 
Finally been cool enough here I can stop running the AC most of the time.
What I notice most is the RPM drop and load on the motor between shifts and of course the vibrations at idle ( RMM ). I don't drive differently but it does make for awkward take-off's and clumsy shifts when I'm not paying attention.

I will say it's been nice in the morning with temps in the mid to upper 60's. Windows down and cool air provides noticeably more power.

Do any of you think the ECU compensates for the AC compressor load? Seems like the car has more pull with the AC on when you get in the throttle far enough to disable it. Maybe it's just the sudden unloading of the motor when the compressor clutch disengages I guess.
 
Any "feel" of extra power you get with the ac on is going to be purely psychological. Like you said, one part woyld be from the already robbed power coming back as soon as you step on it and the compressor stops running.

The other part about the ecu is it probably only tells the motor to increase rpms to compensate for the additional drain of power at idle or off-idle. And thats done simply by opening the throttle a little more, which you could say almost sharpens response slightly
 
I had problem with my AC when I am driving sometimes. Almost like it would work when it wanted to. I'm also from Tampa, and yes the heat is pretty bad at times. Anyways, you could hear the blower blowing, but there wasn't as much air coming out. It did it on the way to get my oil changed today, and I had them look at it. My service manager told me about a TSB from Mazda. (I have an 09 speed3). They changed out a harness to the AC,and it's working fine so far.
 
high3at0209 said:
i live in miami so 60 all day every day! dont think my ac has ever been set higher than that lol
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With respect, are you in Miami. Florida or Miami, Ohio?

My experience with Miami, Florida in the summer is more like this chart:

http://www.weather.com/weather/wxclimatology/monthly/graph/USFL0316

I live on the Mississippi Gulf Coast. Right on the Gulf of Mexico. We've had a huge amount of 95-100 degree temps this summer, as with most. I can't imagine not having air conditioning. Maybe I'm missing something? Are you saying it's 60 outside all day every day, or that you have to set your AC on 60 all the time to keep up with the heat?
 
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Id assume setting the ac to 60

ppl are funny. The only automatic feature i like on this car is the climate control. The auto headlights are unnecessary, auto wipers never wipe when needed or wipe too much, auto window down needs an auto up (makes the most sense when you want the window back up after a toll plaza). Well maybe the auto volume control works pretty well

I cant stand having super cold air blasting me all the time, and as long as the car is moving the system works beautifully with maintaining desired temps, even with with the black paint
 
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