[mjrogers]

Does settting the thermostat @ 80* mix warm & cold air, or shut off ac once it gets down to 80*?

I want to maximize mpg, but not die in 103* heat. Is the thermostat really a thermostat? 8) Other cars ac is either on or off, and if it is too cold they add warm air.

 

[Rick]

From experience the most economical setting for air conditioning is ac on econ 80 fan on full. This will keep you cool. It will blow cold air while the compressor is on and it will warm slightly when it clicks off. Eventually it will stop blowing cold once it's satisfied it's reached the desired temperature, but this usually takes me over 30 minutes to reach.

However, in temperature extremes I would have to recommend that you try more like 75 degrees econ with the fan on full. Mileage goes down, but it will keep the batteries cooler. So far this summer (and it was 112 the other day) I have gotten the car in to complete thermal cut back to the pont where it wouldn't auto stop even with the air set to 80. At 75 I so far have kept it happy so long as I don't keep it at full assist for too long.

Let me give some advise for summer driving. Keep it on the cam as much as possible. Assist = a lot of heat in the batteries and thermal cut back and recalibrations. I love the car dearly, but I'm starting to think they don't belong in the heat. Anyways, the best way is to accelerate normally, but let the thing rev to 4 to 5 thousand rpm in first and second to get up to speed. Usually you can get away with just a few seconds of assist in first gear at the start and a few more seconds of assist in second and then you'll be up around your cruising speed so you wont need it in other gears.

Good luck. 103.... ehhh brisk.

 

[mjrogers]

If it's genertaing the 60* air why not just enjoy it?

What confuses me is that after running the a/c on econ 80*, when I switch it to econ a/c off and dial down to 60* it blows out really cold air until the coils are warmed up.

This makes me think that the a/c is generating 60* air and mixing in 103* air to get to the 80* air. If it's genertaing the 60* air why not just enjoy it?

Does the compressor actually run less often at 80*? Or does warm air just get mixed in to get it up to 80*?

 

[Rick]

Good question. I still think you'd find the compressor comes on less with it set to 80 though. Just seems logical. Suppose it does produce 60 degree air, it fills a resivor in the coils and slowly releases it rather than releasing it all at once causing the compressor to come on more often.

 

[mjrogers]

Guess I was looking for a rationalization to go full blast c

Sounds logical to me. Guess I was looking for a rationalization to go full blast cold w/o guilt :wink:

 

[james]

Of course there's the squirt bottle trick, from the days before A/C was common enough for us peons

Get a cheap squirt bottle with a spray nozzle, fill it with water. When you get in your hot car, spray it around, and the evaporation will cool things down quite a bit. Then your A/C doesn't have to work as hard getting the temp down to something comfortable...

 

[Rick]

Well if you really wanted to get really nuts they do make evaporative coolers that run on 12 volts. They are mainly designed for motorhomes, but I suppose you could just as easily use one in a car.

 

[Will M]

Keep in mind that setting the dial to 80 doesn't make it blow 80 degree air, and setting it to 60 doesn't make it blow 60 degree air. That's not how refrigeration works. When the compressor is on, the interior air conditioner coils are cold. Not 60 degrees or 80 degrees. Just cold. I'm not sure how cold. A wild guess is 40 degrees. The air won't be that cold, but the coils will be.

The air conditioner blows cold air until the interior thermostat tells it the interior air is cool enough to turn off the compressor. If you have the fan set to a manual speed, at that point, the system will start blowing outside air at outside temperatures (unless you have it set to recycle air, in which case, it is just blowing around interior air). It will do this until the inside thermometer tells the system the interior is getting too warm, at which point, the compressor turns on again and the coils get cold.

If you don't have the fan on manual, the system also changes the fan setting, so if it is a lot hotter inside the car than the desired temperature, the fan is on high, and the closer you get to the temperature you want, the slower the fan is blowing. This is just a way to mask the "on/off" nature of refrigeration as we know it.

Keep in mind that turning off the compressor does not immediately stop refrigeration. You'll still have a few seconds of refrigeration as the higher pressure between the compressor and the coil bleeds down through the rest of the system.

Once the refrigeration gasses have stopped chilling the coils, remember that the coils are made of metal and they will still be cold. You'll get a cooling effect until their thermal mass is brought up to the temperature of the air blowing through them.

This is quite enough to explain the chunk of a minute that you still get cold air blowing after you've turned the AC off. Be guilt free.

 

[Insightful Trekker]

In regard to Honda AC system operation:

The system operates by cycling the AC compressor on and off to regulate
the evaporator (the inside coil) temperature. There are other designs
whereby refrigerant flow is by passed to do the same. This regulation
_must_ be done to prevent evap freeze-up.

Honda's automatic AC system does attempt to regulate the interior cabin
temp to the preset value. However, it's not smart enough to decide
whether or not to choose outside air or engine coolant heated air to
achieve this. I believe that it is yet to be determined whether or not
the system is intelligent enough to add a delay cycle to the AC
compressor operation to improve AC on MPG performance instead of simply
adding heat to achieve the selected temp.

Sadly I have not been able to detect a past proven MPG saving logic
which disengages the AC compressor regardless of demand under moderate
to heavy acceleration.

On older Honda Auto AC systems the design allows for a solar radiation
bias and then simply mixes heated air at the correct percentage as the
preset temp approaches the cabin temp. The Insight also has a solar
radiation bias.

So in short to maximize the MPG potential with AC on use manual and set
the dial as high as can be comfortably maintained. This will minimize
the cooling load and therefore minimize AC compressor on cycles.
And use REC when back East. Its not just the heat its also the humidity.
<g> REC will maximize the dehumidification ability of an AC system.

And finally, there is the interaction of the battery pack and thermal
cut-off. For those in hot climates there will be some additional MPG benefit of
AC on operation and available IMA boost. Where the sweet spot on the dial
is will be a tricky to determine and vary widely by driving style.

John K. Bullock
aka. Insightful Trekker