AC setting to save gas?

There are many threads on this topic, but I suppose this one's as good as any.

I recently noted that the blasted heater is practically worse than the AC for power drain! Here in San Diego the day time temps can be around 80-90 this time of year, so I keep the AC in auto and the thermostat at 78. This seems to be a good compromise.

However, in the morning/evening the temp might be at 68. Yesterday I kept the temp settings the same except I had the AC OFF. I rolled the windows down because it was nice and cool outside, but I still felt warm air coming from somewhere! Finally I noted that I had selected the "dual vent" mode from the climate controls, the one that shoots air at your face and feet at the same time. My MPG was in the gutter! (40 for that trip) Now when it's cool outside, I set the thermostat to the same at the outside temp (eg. 70) and make sure that the vent mode is "at your face." I have no need to be toasting my feet when I'm trying to let fresh air into the car!

With this modification, I was able to get 50+ all the way to work today

 

<div class='quotetop'>QUOTE(molgrips @ Aug 4 2006, 08:05 AM) [snapback]297597[/snapback]</div>

I find the system coming up in recirc when first turned on to be a bit annoying. You are correct, when you get into a hot car recirc is not usually the fastest way to cool the car. Around here it's gets into triple digits, and using a digital meat thermomter I have found the inside of my cars often gets to medium rare (140F).

Even if it's 100F oustide, turning the system on full blast with the a couple of windows open by about two inches will blow the hottest 140F air out of the car faster than recirc can cool it off.

I recommend sunshades for parking outside. My rear windows are dark tinted on my Prius and Chrysler. I have measured the temps in both cars during our summer heatwaves and found a huge difference. Window open about 1 inch with shades on the windshield reduce the temp in the car by 25F or more compared to letting the sun beat through windshield with the windows rolled up.

I don't think I have ever seen a climate control that provided the vent combinations you seek.

 

<div class='quotetop'>QUOTE(mike_m @ Jun 6 2006, 03:29 PM) [snapback]266852[/snapback]</div>

It works similary to your A/C-furnace system in that it does things by itself to maintain the temp you select. On your home system, it most likely functions by colling to a selected temperature and shutting off. When the temp goes up by a degree or two (you can adjust the swing on some) the system comes back on. That's a bit "digital" - on or off. The one in your car is little more "analog" than that.

If you start your car with an inside temp of 90 degrees and your auto A/C is set for 73, it is going to start the compressor and blow the coldest air it can make with high fan speed. But rather that just doing this until the cabin hits 73, the fan will kick down its speed as it approaches 73. It will then maintain the selected temp best it can by cycling the compressor (the air from the vent may eventaually not feel as cools as it did at first) and adjusting the fan speed as needed.

If the cabin temp goes below your selected temp (read from the guy in San Diego that left is AC set at 78 when the outside temp went to 68) then the system will start heating. It will autmatically move air to the lower vents (or combination of upper and lower) and increase the air temp.

Using the climate screen, you can overide the vent selection via the climate screen but then the system is no longer automatic. The temp control then becomes more like the blue/red slider control we have all had in cars for years.

Similar will happen with the windshield defogger. Air temp and speed will adjust depending on what temp you have selected - this means you may need to crank up the temp to completely clear your windshield. Also note that during defog, the A/C compressor will run and the air source selector will switch to outside air to reduce cabin humidity.

 

If I'm the only one in the car, I close the passenger seat vents and direct the driver side vents directly at me. This way I can cool off quickly and at a lower setting than what would be required to cool the whole car. Works great for me!

Steve

 

<div class='quotetop'>QUOTE(SteveG @ Sep 15 2006, 12:54 AM) [snapback]319947[/snapback]</div>

I admit not knowing where or how the climate system measures the cabin temperature, but the system will likely be more effective if more vents are open. I only close panel vents as needed when two people can't quite agree on the same A/C setting.

On my other car, the climate control has driver and passenger temp settings controled by two IR sensors (one pointing at the driver, the other at the passenger). Where is the cabin temperature sensor on the Prius?

 

I see no difference in mpg with AC on or off in 100+ degree outside temps when driving the same 90 mile hwy trip three times each week.

 

Having grown up in Phoenix, I still have the habit on hot sunny summer days of turning off the AC, turning the fan to high, and rolling down all the windows as soon as I get in the car. I turn on the AC and roll up the windows after the heat accumulated has escaped and the solar oven I'm sitting in has cooled down to maybe 10 degrees warmer than outside. With the windows up, the AC took way to long to cool an interior down from 150 degrees to 100 degrees in Phoenix, not to mention the energy consumed.

On very sunny pleasant days I like to use the Prius' auto climate control without the AC, by selecting auto and then pressing AC to turn it off. The automatic climate control will then seek to maintain your selected target temperature by bringing in more or less exterior air through the cabin filter. As the cabin cools, it will slow the fans. All the air is filtered for those with allergies. The noise and drag of open windows isn't a concern either.

What I'd like to is how to set the climate control to keep the windshield free of condensation (fog) with minimal energy consumption on cool rainy and very humid days.

 

I have not been able to find simple instructions for cooling the interior of gen 3 Prime (after parking in sun, for example) without the noisy AC compressor starting and using considerable traction battery power.
I'l like to bring in outside air with the fan on high, and a couple of windows open for a few minutes. But there seem to be no instructions in the Owner's Manual that start with "Cool the Interior".

 

Your car is a Gen 3 Prime (based on the Gen 5 Prius, if I'm not mistaken) and this is a Gen 2 thread in which you're posting. Maybe you'd find more answers that are more relevant to your model in the Prime Fuel Economy & EV Range forum. If your search does not turn up anything, you could always post a question there. Or you could try searching the Gen 5 forums.

 

I would leave the entire vent system off for maybe half a mile, with all the windows down. Then roll the backs right up and the fronts about 2/3’s up, start the vent system, on Auto, with AC activated, and run the set temp up till the fan isn’t going flat out, likely around 80F. Another half a mile, or when fan speed starts to drop, tap the set temp down some, and leave the windows just cracked. When fan speed drops a bit more roll the windows right up, and aim for a set temp around 72~74F.

 

An easy to open and close inside reflective screen would help. That huge windshield and dash absorb a lot of sun.

 

I finally found the fan speed display, not where I would expect it or be able to use it while driving. The Owner Manual suggests turning the fan control knob. Hah! The only knob on the entire car is for sound volume.
So I cannot easily control the fan while driving.

 

This is my bug bear: being able to adjust heat/vent controls, without driving off the road. This used to be possible, with tactile/ergonomic controls that could be reached and adjusted with eyes never leaving the road. But we "progress".

 

I use the steering wheel temperature up/down buttons as a proxy fan speed control. It works for me.