A/C is able to maintain cold air without compressor running - how?

That's about how much generation 2 is now of course when it's 95° outside and the sun is shining in a non-tinted car even the Prius this will shorten up quite a bit and it will not happen if the cabin is not stabilized once the cabin is stabilized yeah about a minute is about right and the air will click back on of course ambient temperature and all that sort of thing makes a difference humidity etc but everything seems to be running just fine in your situation.

 

I don't think it's doing anything very special. Now, in cold weather, you keep getting heat when the engine is off, because of a separate electric pump that keeps coolant circulating through the hot engine and the cabin heater core, and so the engine-off time can be pretty long before it has to start again to keep the temperature up.

The A/C, on the other hand, really does stop circulating refrigerant when the compressor stops. There'll be a little continued flow for a moment, just because the high-side pressure is higher than the low side, and the evaporator is cold and will keep cooling the air a little while. It's nice that you've experienced conditions where the engine can stay off as long as a minute. When I owned my Gen 1, in Indiana summers, it was just really annoying how often the engine had to start and stop.

Gen 2, and all later generations, of course went to electric A/C compressors, to put an end to that nonsense.

 

The mass of the evaporator might be a little more than in an econobox. They definitely didn't put a special thermally massive solution in its core or anything fancy like that; it would have been all over the New Car Features manual if they had.

As I said, whatever extra mass it may have makes little noticeable difference in Indiana, but maybe it's something you can notice in Wisconsin.

The electric compressor in the next generation was really a great improvement, and within you really can sit as long with the engine stopped in the summer as you can in the winter.

 

I've had old r12 systems in 74 TE Corollas and once the cabin is stabilized and it basically cuts the compressor it's about close to a minute until it comes back on again of course the gas engine has to be running this is done while driving down the road I remember this very well because these things had an air conditioning amplifier and I could cycle the potentiometers in the amplifier to almost blow snowflakes out the vent which of course meant longer on time for the compressor which is not good for gas mileage or your compressor or any of that but that wasn't the point. So once that little cabin stabilized and it was I don't even remembering like 70° in there if I open the door steam would roll out It was extremely cold once it got to that cold if I was moving down the road and everything was good generally close to a minute 50 seconds you know something like that of course depending upon heat you're in direct sunlight when does your tinted lot of variables but it's similar in a gas car with a reasonably designed system and any of the other stuff mentioned above done helps immensely especially the tinted windows they used to put this lumar film on the front windshield that would knock the dash temp almost 100° lower than the 195 or something that it was

 

I think none of us who work on Prius, whatever call a Prius, Evaporator robust. It’s barely larger and not thicker than my hand, and I don’t have a large hand. Once the age out, they have extreme problem with Evaporator or Leaks are very well-known on Prius..

Different systems operate slightly differently. The way and the quantity of when they’re shut off how much volume of liquid high side is trapped.. in the high side line. As soon as it is switched off it slowly continuously bleeds into the evaporator giving a minute amount of cooling until the evaporator low side pressure just about equals the high side pressure. No temperature difference over one to one ratio and there’s absolutely no cooling after that.. then, depending on the ambient conditions if you have a lot of cold water that has formed in between the fins, water holes, a mass of BTUs as the air passes by it on cooler days you’ll get a little bit of cooling effect from that for a few more seconds.

As for the Evaporators that have the thermal mass in them it’s a wax type material. The best performance from any substance when it either absorbs heat or gives off heat is when it’s going through a phase change.. like when water the energy required to move 1 pound of water, 1°F takes one BTU. If you would move 1 pound of water from 100° to 212°F it would take 112 BTUs of heat to perform that task..
But the move that same pound of water from 212°F into 1 pound of steam. Think of it is trying to make it to 213°F but you cannot.. it takes 970 BTUs of energy to perform that phase change. And the same goes from liquid water into ice in from ice into liquid water..

So, in the case of the evaporators wax, you can choose a wax that has a different melting and liquid point down towards freezing. So you have a few ounces of wax that have to go through a phase change..

And this is good enough for a stop start vehicle when it comes to a stop light, and it’s waiting to give it to occupant a few more seconds of comfort of cooling. Before the engine starts again when the green light comes around..

I remember when they were developing this technology back and talking about it in the early 1990s. It’s nothing new in Automotive

And it’s been around for nearly 100 years in different various forms of refrigeration and comfort cooling.

 

I don’t recall them ever implementing wax or any other substance as a thermal buffering substance

Also, in this country, a prototype they were working on, instead of using the expansion valve use a supersonic combination, centrifugal valving system, internal of the Evaporators that never made it to market.

The wax thermal mass system was something in development back in the late 80s early 90s and the evaporators would’ve had to been a little bit larger in mass with bigger headers. Not a puny little tiny, thin Evaporators on a Prius that are barely thicker than my pointer finger..

They knew the future of stop start vehicles was coming. And they had to do something to overcome conventional air conditioning systems that were engine driven.. when they stopped to give comfort of another 30 seconds of cooling well the compressor stopped.

The thermal wax mass we were discussing in class in automotive engineering in the 80s. I remember going over it in our discussions in class..
Phase change of a substance and the amount of energy that it requires to switch back-and-forth is the basics of when you’re taking thermodynamics classes. Some thing I was fortunate and didn’t know my dad was teaching me back in the 70s before high school just did not know it at the time the value of that education would serve me 20 years later..

With the new heat pumps that are just in their infancy, stage of development in the new electric vehicles, and hybrids in combination with heat recovery in the glycol loop plate heat exchangers.

Thermal management will be the key of keeping engines running on the road