The evaporator is not in the dash in any of my cars, it is in the engine compartment in the false bulkhead area at the bottom of the windshield. I have not located the Jaguar one as yet through lack of interest but I doubt that it is inside the cabin anywhere.

However, I lack interest in continuing this debate.

 

okay the other master tech reading this behind me just called you a mo%^n, I wasnt going there, have a great day someone other than me will correct you

 

http://www.audiworld.com/tech/misc2.shtml

Here's a good explanation for you.

The guy behind you seems to be in the same boat as you so he might want to read this too.

I do know a bit about physics and chemistry.

There are laws of the Universe that prevent your explanation from being correct no matter how fervently you may believe it.

If you drive where it is really cold you quickly realize how this all works.

 

Thats a nice generic 13 year old article, from 1998 and has nothing to do with absolutes of todayshvac systems.
When you stated that you doubted the evaporator was not in the cabin of your xf thats when you just really lost me. Ive worked all jaguars all the back to the 80's and all of them have the evaporator in the cabin. Most manufactures put complete self contained hvac units in cases inside cars today. Just like your xf the hvac unit is under the dash. After you remove the dash, disconnect the coolant lines, ac lines and a couple electrical plugs. The entire unit, blower motor, heater core, evaporator associated sensors all lift out as a complete unit.
Again i have already stated that based upon your temps you see in canada, and what we see in houston, we may both be correct. Out temps below freezing are generally in the 20's, yours are sub zero. So we each see differant operation. We're borderline, your way below. This was to give you and i a amicable gentleman's resolution, but that was not good enough for you and came back with more and the statement that your audi and romeo and no doubt your jaguar have evaporators outside the cabin. Im not speaking on anything other than jaguar. I never pretend to know it all about anything and even though i weork on jaguars all day and for many yrs, its still a learning process. We have to know everything about all systems that are much more complicted than most of the avg cars on the road. You go to a doestic dealer and you see guys/gals that specialize in a system, and dont have to know much else about the car other than that system. And this is on cars not as advanced as most luxury cars are these days.
Now back to jaguar, on your xf, the compressor does not shut off as per my cut and paste directly from jaguars training manual from the very people that know alittle about jaguars. Its always running and is a variable compressor that is controled by the ecu(engine control module) with inputs from the hvac ecu. This is a big improvement over clutched systems that are on/off, because its lets the flow of freon and oil circulate through the system keeping the seals, and compressor lubed, and greatly improves system longevity. I can guarantee that even when its below freezing here in houston(again in the 20's) the clutch on my 1996 xj does engage when i have the system on, and i agree with you and that article on many points but not the compressor does not come on which is what this whole discussion has ensued on. And again, for what you see in canada in the winter i have no doubt you dont see a clutch on your older ac systems come on. But we are speaking of 2 differant condition now arent we, and would you agree that under both of these conditions that again ill restate that both of us may be correct???? (other than your jaguar which ive already pasted that it uses a differant compressor that doesnt shut off)
im sorry if your feel offended by me, i felt offended by your statement of " you dont seem to understand the very car you work on every day!"

 

Science presumes that the laws of physics and chemistry have remained the same since time began, although that may not actually be true. Certainly we know that the laws of physics and chemistry have not changed for over 300 years. What you describe cannot occur. The age of the article I referred you to is irrelevant. AC works with the same laws of physics and chemistry now as it did 13 years ago.

If you could explain how air colder than freezing could deposit liquid water anywhere (the drying effect you refer to) you could make a huge pile of money proving the laws of physics and chemistry have been altered. Although you may not realize it the air that is "dried" by the AC evaporator isn't really, the cold air is just as "wet" as the warmer air it began with, "wetter" actually. It is subsequent heating of that same air that effects the "drying". That is why we refer to "relative humidity". The AC only incidentally removes moisture from the air because cold air cannot hold as much water vapour as warmer air. You cannot design an AC system that does not do this or refrigerators would not have to have "frost free" heating elements to prevent the refrigerator from icing up. In dry climates this drying effect is a negative characteristic of AC systems.

The initial post was about cold weather fuel consumption. It was suggested that switching the climate control from Auto to Manual could reduce fuel consumption. That is not the case. The climate control does not consume power when outside temperatures are below freezing.

I know this because you cannot dry or cool ambient air with moisture in it, i.e. ordinary outside air, by trying to draw it through a cold AC evaporator. The moisture will freeze and block the evaporator. Just heating the outside air will "dry" it. The windows frost or fog up because they are nearly as cold as the outside. It helps if the air inside the car can be made slightly dryer than the ambient air until the windows warm up a bit. In very cold weather it is a good thing the outside air is so dry.

You say this isn't how it works but are unable to explain how it does work in terms that I can follow. Bottom line, you also say that the "modern" AC system in the Jaguar will not consume less fuel if it is switched from Auto to Manual. Whether that results from a more efficient "scroll" type compressor that, in effect, idles when not pumping refrigerant or because the compressor idles when an electromagnetic clutch disengages the drive pulley is irrelevant to the issue of fuel economy. The effect is the same: less power consumption when the compressor is not compressing refrigerant.

Relevant to the topic of the thread: we both agree that the climate control can be left on Auto in winter without causing fuel consumption to rise. Incidentally, to add insult to injury, the Jaguar XF climate control system is an inadequate design for Canadian winters because it will not warm up the glass or dry the air sufficiently to keep frost off the windows at minus 20C or colder. The heater also delivers far too much heat to the floor of the car and not enough volume of air to do the job effectively and comfortably.
On a related issue, the cold air will indeed permit the engine to develop more power at a given throttle opening but this does not affect winter fuel consumption. As another poster pointed out, this means the engine can be run at slightly less throttle at any given load which evens out the fuel consumption. Admittedly, pumping losses are slightly higher with the throttle closed a bit more but that is unlikely to be a significant factor in fuel consumption compared to all the rest of the possible causes.

Fuel is also sold by temperature adjusted volume which impacts the actual quantity of fuel you have purchased by volume. In Canada, and other civilized places that prevent suppliers from cheating their customers, the law requires that the service station delivery pump adjust the measured volume to match the same mass of fuel at a stated temperature. In Canada that temperature is 15C. The actual volume delivered is less in winter and more in summer. So, when fuel economy is calculated by miles per unit volume the mass effects you are actually referring to are cancelled out by the delivery pump. Put another way, cold air may require more mass of fuel to meet the ECU mixture values but the displayed volume of fuel that you recorded as pumped into your tank was overstated by a proportional amount. Logically, fuel should be sold by weight (mass actually) but instead it is sold by temperature corrected volume to approximate the same mass regardless of temperature. We still calculate fuel consumption as if volume equated to energy content, which of course is incorrect.

Hope that all helps anyone who may still be interested in this way off topic thread.

 

OKay fine you win, the evaporator isnt inside the car on a Jaguar, the compressor does shut off when freezing(it does and I already thought I stated that when the evap temp sensor goes below freezing it shuts off the compress, and this is true regardless of the outside temps cause you can freeze and evap even in the summer) And maybe Im mistaken about the latent transfere of heat and abilty of air to either hold or release water under differant conditions. Youve beaten me into submission and science, but I do know that when engineers "engineer" something I am the one called on to fix it...also did God create man or did we evolve, thats another big mystery for many. What does SCIENCE say about that. science hasnt changed in 300 yrs please is that why george Washington died because science said to heal him doctors needed to blood let him. Science is always changing. Wait long enough and fact is fact or fiction today will be the opposite in the future.
Again congradulations I know why you can afford a XF and I cannot, your smarter than I am. so you can now answer all the questions about peoples Jags on here now Im out