Went to the mountains in our Prius

[jendbbay]

<div class='quotetop'>QUOTE(donee @ Aug 5 2007, 06:08 PM) [snapback]491001[/snapback]</div>

Hi Sufferin..

Who is insisting on anything? Your quote was not in the original post, or before any post I made. The system probably works to ensure comfort level. So, with lower temp, higher humidity might still be a net confort level improvment. AND, I did leave the posibility open in my post regarding thermal load change, without specifically mentioning it. That was in my thinking as a possibility when I wrote it. But, I wrote the comment as if the OP had been complete in her original description, and had told us the whole set of facts. Specifically, the temperature was still 94 F when she opened recirc.

Another thing is that the amount of water vapor air can hold at higher altitude and lower temperatue is less (in both cases). There is less water vapor in 70 degree 50 % R.H. air than 94 F 50 % R.H. air. So, flowing outside air inside would automatically dehumidify the cabin, not only by dilution, but difusion. Besides cooling the cabin air, as the outside air is now cooler.

So, dehumdification could still be the issue. As why did the AC still pull lots of power when the recirc was closed? If the air was cool outside, the thermal performance of the AC would have been allot better. But she reports only after opening recirc did vehicle power improve.

The AC could have still dropped out of dehumidification mode, and even turned the compressor off, as all cooling and dehumidification would have been provided by ventilation.

The hypothesis here is that an automatic dehumidication mode could still be the root cause of the high AC power demand in this case.
[/b]

I am the OP and I know when I switched to fresh. It was STILL HOT. At the moment I pushed the button to fresh, the engine received substantial additional power -- in other words returned to normal. Prior to pushing the button it had lost about 40 per cent (to my untrained mind and senses) of its normal power.

Soom thereafter the external temp started to drop. This started happening about 5 minutes or so later. That was a good thing, in general, but I don't know of any impact it had on the power, since the power lost had already resolved itself for some reason.

I so appreciate all these insights.

jennifer

[jendbbay]

<div class='quotetop'>QUOTE(donee @ Aug 5 2007, 06:08 PM) [snapback]491001[/snapback]</div>

Hi Sufferin..

Who is insisting on anything? Your quote was not in the original post, or before any post I made. The system probably works to ensure comfort level. So, with lower temp, higher humidity might still be a net confort level improvment. AND, I did leave the posibility open in my post regarding thermal load change, without specifically mentioning it. That was in my thinking as a possibility when I wrote it. But, I wrote the comment as if the OP had been complete in her original description, and had told us the whole set of facts. Specifically, the temperature was still 94 F when she opened recirc.

Another thing is that the amount of water vapor air can hold at higher altitude and lower temperatue is less (in both cases). There is less water vapor in 70 degree 50 % R.H. air than 94 F 50 % R.H. air. So, flowing outside air inside would automatically dehumidify the cabin, not only by dilution, but difusion. Besides cooling the cabin air, as the outside air is now cooler.

So, dehumdification could still be the issue. As why did the AC still pull lots of power when the recirc was closed? If the air was cool outside, the thermal performance of the AC would have been allot better. But she reports only after opening recirc did vehicle power improve.

The AC could have still dropped out of dehumidification mode, and even turned the compressor off, as all cooling and dehumidification would have been provided by ventilation.

The hypothesis here is that an automatic dehumidication mode could still be the root cause of the high AC power demand in this case.
[/b]

I am the OP and I know when I switched to fresh. It was STILL HOT. At the moment I pushed the button to fresh, the engine received substantial additional power -- in other words returned to normal. Prior to pushing the button it had lost about 40 per cent (to my untrained mind and senses) of its normal power.

Soom thereafter the external temp started to drop. This started happening about 5 minutes or so later. That was a good thing, in general, but I don't know of any impact it had on the power, since the power lost had already resolved itself for some reason.

I so appreciate all these insights.

And as to the following quote:

So let's see: Partway up the mountain you switched from recirc to fresh, and at the same time the outside temperature was dropping from 94 degrees down to the high 70s - and yet, somehow, you people are trying to attribute the additional available power to the dehumidification aspects of air conditioning?

IF changing from recirc to fresh had any affect on the car's performance, I doubt it had anything to do with dehumidification.
Dehumidification happens when warm moist air come in contact with the cold fins of the evaporator unit. This happens whether the car is in recirc or fresh air mode.

If anything, if we are going to try to attribute the increased performance on changing from recirc to fresh air, my guess would be the extra cool air being blown through the traction battery helping keep it cool. If you are forcing air into the car, it also needs to escape, and the traction battery vent is the most logical place.[/b]

Nope. We had been climbing the mountain for about 45 minutes to an hour when this happened. It happened before the temp. dropped, but not long before. The temp was still over 90 when this happened. Nothing at all went wrong when we were driving across the valley and the problem never came back again. Pushing the fresh button was so linked tothe change in engine power, that relating the two events was super hard to resist doing.

The theory about forcing air into the battery is the winner theory in my opinion. I think that was it.

Again, thanks to all who gave inputs.

Jennifer


jennifer

[telstar]

<div class='quotetop'>QUOTE(jendbbay @ Aug 6 2007, 12:35 PM) [snapback]491343[/snapback]</div>

I am the OP and I know when I switched to fresh. It was STILL HOT. At the moment I pushed the button to fresh, the engine received substantial additional power -- in other words returned to normal. Prior to pushing the button it had lost about 40 per cent (to my untrained mind and senses) of its normal power.

Soom thereafter the external temp started to drop. This started happening about 5 minutes or so later. That was a good thing, in general, but I don't know of any impact it had on the power, since the power lost had already resolved itself for some reason.

I so appreciate all these insights.

And as to the following quote:
Nope. We had been climbing the mountain for about 45 minutes to an hour when this happened. It happened before the temp. dropped, but not long before. The temp was still over 90 when this happened. Nothing at all went wrong when we were driving across the valley and the problem never came back again. Pushing the fresh button was so linked tothe change in engine power, that relating the two events was super hard to resist doing.

The theory about forcing air into the battery is the winner theory in my opinion. I think that was it.

Again, thanks to all who gave inputs.

Jennifer
jennifer
[/b]

I made a similar comment on another thread about this general (AC setting the subject of less MPG) subject --- but it used to be that when the AC was on recirculate (older cars & systems) the compressor would run steadily and would not kick off and on. When the AC was placed on the refresh setting (or normal setting) the compressor would start kicking in and out as needed & bringing outside air into the cabin. IF that occurs with the Prius (recirculate causing the compressor to run all the time) then it follows that more power is being drawn during recirculate mode, and less power is drawn in the refresh or normal mode. If this holds true then the other factors in your situation may have contributed enough for a noticable difference in power output of the engine/motor.