Nearly three months ago we purchased a brand new 2007 FEH. I knew about the issue of the air conditioning being driven off of the ICE and that turning on the air conditioning forced the ICE to stay on all the time. We live in New Hampshire and the weather has started to change so we have started using the defrost and we have now discovered that turning on the windshield defrost causes the air conditioning to come on automatically and thus keeps the ICE on. Is there a way to run the defrost without the air conditioner that we don't know about?

 

The short answer is "no". Ford, like many, if not most manufacturers has set the AC to run anytime the defrost is used as indicated by the red color of the defrost icon. This dehumidifies the air and clears the windshield of moisture more quickly. It also makes the MPG drop. The same thing happens in my 2002 Honda Civic (non-hybrid). I've found that if you have the heat on some air leaks through the defrost vents, usually enough to keep the windshield clear in all but the worst situations. The most efficient technique would probably be to run the defrost on initial startup (when the engine runs for several minutes no matter what you do) and at times when the ICE would be running anyway, then switch to normal cabin heating when EV mode is possible. Fuel economy takes a hit in the winter anyway due to keeping the catalytic converter and other systems warm.


Another option, if the humidity is high and the windshield won't stay clear with just the heat, is to run the AC in normal mode (not MAX) with the heat turned up. This will both heat the cabin and dehumidify the air, hopefully taking care of the condensation while not running the ICE continuously.

 

Leaving it on the normal AC mode has been working very well for us. The hybrid system functions normally, and unless you've got a carload of heavy breathers, does a decent job of keeping the windows clear.

 

If needed I just flip the defroster on when I see the engine kick in. When I slow down or stop I just flip it off.

 

Our weather has started to turn as well so I turn on the AC or defrost when I start the FEH in the morning when the ICE would be on anyway. Once the car warms up and the initial frost is gone from the windows I open the driver and/or passenger side windows a crack and it keeps the windows from frosting back up.

 

History just keeps repeating itself.

Before the advent of these automatic climate systems, first encountered by myself in my then new 1984 T-bird Elan, it was my practice to ALWAYS disconnect the A/C compressor clutch circuit during the winter months.

I have live in the Seattle area so keep in mind as you read the following that our climatic conditions during the winter may vary radiacally from those you might encounter in say, Arizona. What I have determined in my 40 some years of driving primarily here in the Seattle area is that the use of the A/C for other than cooling is 'way too often detrimental for its operation to be trustworthy in cool or COLD climates such as exist here.

The problem is that the A/C can only rarely be relied upon as an efficient method of lowering the humidity of the incoming fresh airflow when the OAT is at or below ~47F. When the OAT is in the range when it is not needed for cooling and until it decline sll the way down to 35F the efficiency of the A/C to lower the RH of the incoming airflow is TOTALLY RANDOM. I assume we all know that below ~35F the probablity of the A/C being efficient enough to be used for dehumidification is so close to ZERO (at 31F it is ZERO) most manufacturers disable the A/C below ~35F.

Yes, the A/C was often used to aid the defrost/demist/defog functionality prior to the arrival of these automatic climate control systems ariving in the marketplace, but the difference was that along with the A/C there was ALWAYS a goodly amount of HEATING of the windshield directed airflow.

A/C "linked" "on" in defrost/demist/defog mode? Along with HEAT, no foul, no FAULT.

So my practice of disconnecting the A/C during the winter months back then had no ill effect.

But not with the advent of these new automatic climate control systems. Apparently when these were being designed it was decided, for some unknow reason, that the A/C could be used EXCLUSIVELY for defogging/demisting the interior surface of the windshield one the cabin temperature, atmosphere, has been raised to human comfort level. The only explanation for this that I have been able to think up/of is the issue of the fairly high discomfort level the front seat passengers will be forced to endure with that HEATED defog/demist airflow reflecting from the interior windshield surface.

Actaul defrosting, however, is treated differently, for good and sound reasons.

In the general case, or maybe even in all cases, the only time the windshield will need DEFROSTING is after it has been parked out in the cold for a period of time. So defrost is handled correctly by these new automatic climate control systems. As long as the IAT sensor's signal indicates that the interior AIR temperature is at least slightly below your comfort level, as determined by the system setpoint (72F..?), activation of the defrost/defog/demist mode will result in activation of the A/C, (sometimes, if it was previously off, with no indication to you) along with, as the engine water jacket temperature rises, HEATED airflow routed to the interior surface of the windshield.

Actually this new system will work perfectly fine as long as no UPSET conditions occur.

Say loading 2 or 3 wet (soaked) and sweaty snow skiiers after driving up to the pass to pick them up. The cabin atmosphere will be at or very near your setpoint so once the windshield begins to fog over (IT WILL) and you respond by activating the demist/defog mode what you will get is lots of cool and very humid airflow to a windshield that has already been pre-cooled below dewpoint during your drive up the pass.

Guess what, now you have NO forward visibility due to the THICK layer of condensation on teh windshield.

My advice?

Disconnect the A/C compressor clutch circuit during the winter months and be quick to turn up the system heat demand when you (prior too, actually) activate the defrost/defog/demist mode.

How do we/you prevent FEH/MMH ICE activation in defrost/demist/mode?

The automatic climate control ECU's signal to activate the A/C compressor clutch travels to, through, the engine control ECU. That's so that ECU can disable the A/C during WOT operations. Find the signal wire to the engine ECU, open it, and the engine will no longer start due to activation of the defrost/defog/demist mode.

Since ~2001 Toyota and Lexus vehicles have had a c-best option wherein the A/C can be indefintely disabled, through multiple, infinite, restarts, by simply turning it off one time. It will then remain off until you turn it back on. A second c-best option "unlinks" the A/C from operating automatically in defrost/defog/demist mode.

Of more recent times, 2004(?), another c-best option has been added to prevent the climate control system from automatically switching from footwell to the upper, dash, airflow outlets as the cabin warms to your setpoint.

The effect of this is fairly discomforting, cool and dry airflow to bare skin, face and upper body, at a time when the human confort equation will likely be put out of balance due to the radiant effects of the COLD surrounding "landscape". But with Toyota and Lexus vehicles the effect resulting from the automatic switch from footwell airflow might be even beyond discomforting, deadly even.

In footwell, heating, airflow mode a significant level of that WARM airlfow is intentionally "leaked" to the windshield interior surface, presumably, traditionally, to keep it's interior surface heated to well above the dewpoint of the cabin atmosphere.

Think about this....

I lift Seattle with myself and three passengers headed over the I90 pass to Yakima one bright but coolish late fall day in my nice new shiny 1992 Lexus LS400. Everything appeared normal until we reached the area were the roadbed is predominantly rising, then the final incline to the top of the pass, the roadbed is snow packed, and it is snowing.

Now I happened to notice small wisps of condensation beginning to form at the bottom outside corners of the windshield. So I reach over and depress the defrost/defog/demist button.

BLAM...!!

Suddenly the windshield becomes so thoroughly fogged over that I have NO forward visibility.

Panic..? You bet, in spades.

No towel handy, depressing the HIGH blower buttom seemingly makes matters worse, and it takes forever to depress the temperature setpoint "up" button enough times to raise the system output temperature to a level that will result in subsiding of the rate of condensation on the interior windshield surface. So much so that my wife assumes that task telling me to keep my attention on the roadbed.

Finally I realize that lowering the windows will help and the windshield fogging subsides fairly rapidly once the rear windows are completely down.

WHEW....

It took me almost a year to gather enough information to begin to understand just what had happened that day. After a repeat episode the following January teh Lexus remained parked in my garage with Lexus saying that the climate control was operating as designed.

It sure was. Flawed design, but....

 

Continued...

I have very little doubt that long before we reached the area of predominantly rising roadbed the Lexus climate control system had raised the cabin air temperture to my 72F setpoint and then automatcally switched from footwell outlet airflow to the dash, cooling mode.

Part of what I was to learn was that in the LS400's "cooling" mode there is NO intentional leakage of air to keep the windshield warmed and the small amount of airflow that does "escape" via the windshield airflow ducts does not flow through the system's reheat/remix path.

Additionally even if I had noted the switch to "cooling" mode, known of its potential for being the root cause of the upcoming hazardous experience, and manually switched it back to the footwell, heating mode, it most lekly would have not prevented the episode.

Had I even known to switch the system back to footwell mode manually, the resulting airflow from the windshield ducts, have not passed through the system's reheat/remix "path", would have been as much as 20F cooller than my 72F system setpoint.

But I didn't.

So as we drove along on that increasing colder rising roadbed the interior surface of the windshield also grew increasing colder due to the impinging outside COLD airflow at ~65 MPH.

Now we reached a certain point, distance wise an unknowable point, wherein the OAT had declined so low, perhaps 35F, that the system automatically disabled the A/C compressor clutch. If you happen to know to watch, the A/C indicator will silently extinguish.

Now the incoming airflow is below freezing and its RH is therefore likely very low, in all likelihood low enough that its RH, alone, could not result in any substantial level of windshield condensation.

But that incoming COLD and DRY airlflow, ALL of it, must pass through the A/C evaporator. As it happens an evaporator that is current absolutely CLOGGED with moisture due to the previous A/C compressor operation, having just arrived "here" from a much more humid climate.

So now the stage is set, fully. Te climate control system is in cooling mode, the windshield is most throughly CHILLED, the A/C is disabled and canot be reactivated absent a rise in OAT. The thin film of condesation remaining on teh 10,000 square inches of evaporator vane surface area begins to slowly evaporator into the DRYER incoming airflow.

I spot the wisps of condensation and activate the defog/demist function.

Now suddenly ALL of the system airflow, undoubtedly HUMID airflow, is routed to the windshield.

BLAM...! (am I repeating myself?)

Turn up the blower speed, more humid airflow VOLUME to the COLD windshield.

My 1992 Lexus Ls400 now has a modification wherein I can flip a small toggle switch just prior to activating d/d/d mode. The switch adds a resister in series with the IAT thermistor sensor making the climate control ECU "think" the cabin has suddely grown VERY cold. So activating that simple switch causes the ECU to raise the blower speed to max and close the remix bypass vane fully so ALL system airflow will be heated.

The same DPST switch supplies power to two 12 volt computer "boxer" type fans/blowers mounted within the trunk to more quickly extract humid air from the cabin by exhausting it out under "pressure" via the standard "exhauster" ports at the bottom of each rear quarter panel.

 

The rest of that is all very interesting, but this advice is just flat impractical. Eliminating AC operation during cold or humid weather leaves one at the mercy of heating and raw volume of airflow.

So what, do you do in weather of say 60 degrees with a carload of wet soccer players and you need to leave in a hurry? Without AC, you wait.

I'm not suggesting that the old standby of heat and airflow won't do the trick, but one could remain waiting there for several minutes for effecting defogging. Switching AC on immediately provides far quicker defogging, shortened idle time - AND SAVED FUEL.

For the most part, it is a time saving convenience and comfort item. But disconnecting it is silly IMO.

 

I, too, am annoyed by this, and am taking matters into my own hands. I am working on adding a switch to the right of the SET switch, and using it to toggle between Green AC, Forced AC, and No AC. This means I will be disconnecting the AC control signals from the function switch, but will still be able to use my AC.

The details of this effort will be forthcoming, but probably won't be until early next year. The project is not necessarily simple, but in essence there are two wires that connect to the AC system. One forces the AC/ICE to be on, and the other simply requests AC when the ICE is already on.

I bought a spare hazard switch, and will modify it to control my AC.

 

SNAX...

Our daughter, soccer mom, has at her disposal a MY 2000 AWD Chrysler T&C minivan and believe me, she well knows the optimal procedure to use after she loads up that soccer team.

The Chrysler has rear quarter panel windows that can be opened, maybe 15 degrees max, from the switches on the driver's door panel. I think you will readily acknowledge that even with the OAT at 60F, the A/C must get the cooling evaporator down to its 35F operating range before any reliable level of dehumdification of the incoming fresh airflow will/might occur. Do you happen to know just how high the RH of the 60F outside air must be so as to be at or near the required 100% RH when/if the system can reduce its temperature to that level. I don't, look it up.

But now let's suppose my daughter happens to have the system setpoint at a nice comfortable 72F... How fast will the blower speed be, automatically, to most quickly bring the cabin temperature up to her setpoint?

And why am I bringing up the issue of blower speed?

Because the faster the air flows through those 10,000 square inches of sub-35F evaporator cooling vane surface area the less it will be affected by the COLD of those vanes.

So, to keep the windshield from fogging up....?

Turn the blower speed up max, switch the system to 3D mode, and open those rear vents.

Keep in mind that in the situation you describe the RH (airborne moisture) and the source for even more, is ALREADY inside the van. It will now take lots of airflow moving through the van to most quickly remove all of the potential for fogging over the windshield.

And other than lots of airflow along with an easy entry and exit path, what is the most reliable and predicable method, additionally, that anyone should turn to first, next?

Simple: Reduce the RH of the incoming airflow by heating it as much as your personal comfort level allows. Turn on the A/C? Sure, but only for backup.

But it would not be adviseable that one turn down the blower speed to bring the dehumidification capability of the A/C into play unless one could be certain that it would be substantially beneficial.

Say an outside atmospheric RH display/indicator suctioned to the windshield right were you can read it. And do you know how high that outside RH must be in order for the A/C to be really, reasonably, efficient?

No...?

Turn the A/C on anyway, it can't hurt provided you use the other methods first and foremost.

Can't hurt...??!!

Sorry, I mispoke.

When you subsequently turn the A/C off, all of the moisture remaining, at that moment, on those 10,000 square inches of evaporator vane surface area will now evaporate into the airstream headed for the passenger cabin. If that happens at the end of the day, say within your garage, that moisture will likely hang around for several days awaiting the restart of the blower so it can be exhausted into the cabin, and hopefully quickly beyond.

Oh, did I forget to mention that that retained moisture on the evaporator vanes and within the A/C plenum area is one of the primary causes of the dirty gym sock odor, mould and mildew, that many owners experience.

Go to airsept.com and read up on their EED for a solution.