Captain_Slow

An AC system will have an easier time cooling warm and dry air than hot and humid air because of the release of latent heat due to condensation. It's the same process that causes the dripping water under the car. Obviously it is more work to cool hot air, but moist air makes the system much less efficient. Directly or indirectly energy from the Sun warms liquid water until it evaporates - and the energy is stored as the kinetic energy of the water vapor molecules. This is called the latent heat of evaporation....energy which is removed from our environment such that latent heat is kind of hidden while it is stored in the evaporated state (it's why we are cooled by sweat evaporating from our skin). The latent heat of evaporation only seems hidden or removed, because like all energy it must be "conserved"..again, the latent heat was stored as the kinetic energy of the faster moving water vapor molecules. The reverse happens when water vapor molecules slow down and condense back to liquid. In your AC system the water vapor condenses on the evaporator because its temperature is far below the dew point. As the hydrogen bonds between water molecules are restored it becomes liquid and the latent heat is released - returned to the air flowing through the evaporator, and WARMING the air. The amount of energy released is significant (on a larger scale it's what powers the weather.. hurricanes, etc.). On a really hot and humid day in Miami there should be a big puddle forming under the car and the air coming through the vents may only be cool...barely adequate.

So...there's not really a tipping point aside from the moment freezing starts. I'm amazed by the 18F reading. It is likely the latent heat of condensation (and/or very low humidity) that prevents the evaporator from freezing - and it being clean so that condensation drips off immediately. My home AC/Heat Pump unit will freeze up in winter, but it is doing the opposite - extracting heat from the outside air and putting it in my house...the details don't apply here.

merchauser

what can be expected with the upgraded condenser? big difference in cooling? for 500. I would
hope???

Christopher Zach

Ah maybe that is the problem: It has been so wet and humid here the cars are dripping water like mad. Yesterday I briefly wondered if I had holed the radiator on the prius.

Still, I'll measure some air temps with my IR gun over the next week and see what the inlet and outlet temps are at the condenser.Data is good.

skpyle

928NOOBIE

Today I took it out and drove around to stress-test the engine from a cooling perspective. I had the AC and temp set at 75 degrees which allowed it to pull air from outside and it performed flawlessly...was it 18 I don't think quite but it was very cold...switching to recirc quickly brought temps down into the range I shared earlier...just frigid cold...

So I drove to a place called the Country Club Plaza...anyone familiar with KC knows it's an outdoor shopping center with streets with lots of stop and go ....perfect stress test...I had my IR gun handy...I had the air on...the cabin was plenty cool...note it came out of a cool garage (partially submerged underground) and I recently got tint done including an infrared coating on the windshield that blocks 80% of infrared hitting the dash...it has made an unbelievable difference.

So sure enough...my white needle goes so it's just touching the upper white line...I pull over...leaving the car running with AC on and begin to take temps...I take temps on the hot-tank side from the front of the car...why? Because surface temps from anything facing a radiating heat source are going to reflect higher temps and I wanted the temp of the coolant in the hot tank...plus I didn't take it from the fins because the condenser pusher fan was running and the hot side of the condenser was in the 170s...so...the hot tank was registering about 190-193....I took temp in several places (as space would allow) along the hot tank and that was about the hottest I could find...so well within the upper range...

I next moved to the cold side....I took the IR surface temp of the cold radiator hose ....190-200...yes...definitely getting high surface temps due to the radiant heat given off by the engine....switch to the cold side tank on the front of the radiator...140, 135, 150...much more in line for what I would expect going through 928Int'l's special rad they had made for us...

So from my perspective..my needle is correct at just below the white line...but I also believe it's being slightly paranoid...as I couldn't find a place on the hot tank reading 200...maybe 195 was really it....I also as space allowed took multiple temp readings of the cold tank and got multiple readings as I went down...but 155 was the highest I recorded....most were in the 140-mid 130's range...
I'm really happy I did this...it was in low 90's with very high humidity...so the AC was working pretty hard..even though it had a good start with no ambient heat on surfaces it had to overcome...so the fan speed was on 2 and with the temp at 75 it was switching between fresh and recirc on a regular basis and seemed very happy.

We stopped at the Amoco for a big drink of 93 and the car was properly draining water from the evaporator...though not a river as I would have thought...I don't think I was experiencing any freezing, as when the car switched to recirc there was a significant increase in air-flow...along with the appropriate increase in noise as the cabin door opens...

So I am thinking on recirc ...with my set up it's probably able to achieve very close temps as I shared earlier..if not the same...it's not pulling in air that's been warmed by surfaces that are super hot from the sun and on recirc the air is very dry...I also like the temp setting so it does flip back and forth to ensure nice hot air is hitting the evaporator...helping to hopefully ensure against freeze-up.

I do think I have a leaf that's sometimes brushing against the fan...but that's another story for another day...cheers all!

Kevin in Atlanta

Cool. And DR made a sale. Everybody wins.