I had this happen a couple of weeks ago on a hot day in heavy traffic with no A/C running. I don't recall why I was not using the A/C on a near-100° day but... I do remember it was really hot. I think I was trying to be "economical".

It occured after about 20 minutes in traffic. Not sure why it happened but, whatever the reason, it was suddenly very obvious that there was neither any electric assist nor any regen braking happening. It lasted until I got on a highway and turned on the A/C. Hybrid operation didn't return until I had driven at steady speeds with A/C on for a while.

My best guess is that the battery was too hot. Previously I had guessed that the vehicle would recognize that situation and run the ICE + rear A/C if battery temp got too high. However, it appears this is not the case and that it actually shuts off all charge/assist instead. Anyone else have this happen?

 

Design engineers may have decided that you would get too hot before the batteries. But if so that might open the door to a modification so there is no WASTEFULL electric assist in/during highway cruising when the only recharge capability would be the ICE.

Simply modify the battery temperature sensor so the control system "thinks" the hybrid battery is over-heating.

And by-the-by it must always use the electric "assist" to run the CVT's low HP differential drive motor.

 

No A/C? Were your windows down? There used to be a debate as to whether it was more efficient to run with windows down vs. run the AC. Turns out in _most_ modern cars, the AC is always more efficient. In the case of the FEH, Ford says the AC is *definitely* more efficient than driving with windows down -- and this is true at almost any speed, not just freeway speeds.

 

Yeah, no A/C in 100°. Silly, eh? I'd been exercising and was overheated and the dry breeze felt good.

As far as A/C versus no A/C ...

I remember the TV show "Mythbusters" tried to test this a couple years ago. They started with a computer model showing aero drag should be more than compressor drag. But then for some reason they could only do the test at 50 MPH. At those speeds A/C used measurably more fuel. No surprise there, since wind drag from windows isn't much of a factor at 50 and A/C is a factor at and speed above zero.

One of the car mags did a better test, but it was years ago and I only remember two things from it: At highway speed A/C was technically best but the advantage varied by car. Under 60, both compressor drag and windows-open aero drag were measurable but so small as to be considered a non-factor. They basically said to use A/C on the interstate but otherwise to do whatever makes you comfortable, since the MPG loss at lower speeds was not worth sweating over.

 

I personally had a hard time believing that A/C was more efficient at "any" speed. Air density increases exponentially as velocity increases -- so there's a point where at low speeds there just isn't enough "density" for the air to create much noticable drag. I would think anything below 25 mph would have such minimal drag that it wouldn't be measurable.

At 35 or 45 I can definitely believe it though. I've been out sailing when winds kick up to just 35 mph and even with no sails on the boat, that much wind is really noticable.

I don't know enough about automotive A/C compressures to be sure, but I've read info which seems to suggest that the temperature setting effects how much "drag" the A/C compressor makes. On a house the A/C thermostat either has the AC "on" or "off". The compressor runs the same when it's on. Dialing the thermostat up just causes the A/C to run less often or for shorter periods.

But Ford seemed to indicate at the owners' event they hosted that switching to recirculated air and turning down the temp would actually cause the compressor to work less hard -- and reduce the energy needed to run it. This was back in the '05 model year before the introduction of "climate control" (we '05 owners can't set our temperature... we just have the warm/cold blend dial that controls how cool the air is that blows out.)

Anybody know how that works? Why would the car use less energy to run the AC by turning the temperature dial up? Does the compressor somehow not pump as hard (which is not at all how an A/C compressor or any other refrigerant compressor would work)?

 

The FEH until 08 has a manual a/c system. In this system the compressor runs continuously or until the low side pressure is near freezing. Warm heated air is blended with the a/c cooled air to controll the duct temp. This is done with the cold/warm ****, a cable and a blend door. The a/c system has a pressure switch that will shut off the compressor when the low side pressure is about 29 psi. This pressure corresponds to about 33 deg F. This is done to keep the evaporator from freezing into a block of ice. So if you turn the cold/warm **** to cold and reduce the blower the evaporator will receive less heat and it will drop in temp causing the pressure switch to cycle shutting down the a/c compressor for a few seconds or till the pressure rises to about 40 psi. I have been considering adding some kind of thermostat to the system via this pressure switch to cycle the compressor instead of blending heated air to warm the a/c. This would probably result in some savings on the highway.

 

The base problem is that A/C cooling cannot be directly modulated. When the refrigerant transitions from a liquid to a gas it does so below 32F. Think of it this way, absent changing sea level air pressure how could you regulate, moderate, modulate, the temperature, 212F, at which water boils?

Since you cannot, at least not easily, "regulate" the temperature at which the refrigerant "boils", the only way to moderate the temperature of the airflow exiting the cooling evaporator is to reheat all, or a portion, depending on just what temperature you want the final air outflow to be just before it hits your face.

If you wish to modify one of these modern day systems in order to dramatically improve the A/C efficiency and the FE somewhat and at the same time not be discomforted by the COLDNESS of the system airflow there is an alternative method available.

Instead of reheating a portion of the system airflow simply "mix-in" enough of the cabin atmosphere, say at 72F ambient, such that the airflow striking your face and upper body isn't so discomforting.

But. Not exactly a simple modification.

Your must open an air inlet "port" downsteam of the A/C cooling evaporator for entry of the cabin air, atmosphere. Then you must provide a fan or blower to control the level of cabin airflow entering this new port for mixing with the system airflow as it exits the cooling evaporator. Now you must design a control system that controls teh speed of the new blower, in relation to the speed of the OEM blower, in order to control the airflow
MIXING ratio.

There is yet another design issue to take into consideration. Dehumidification.

The lowest temperature the incoming fresh airflow is cooled to the higher the probability there will be a measureable level of dehumidification. Our human comfort level does somewhat depend on a fairly low level of relative humidity of the local surrounding atmosphere. But insofar as automotive A/C is concerned keeping the RH as low as is possible also reduces the possibility of interior windshield fogging.

So, it is highly desireable to reduce the temperature of the incoming fresh airflow, at least temporarily, to the lowest possible temperature, in this case no lower than ~33F.

 

TIM TIM TIM!!! No! No! NO! This is exactly backwards!

FOR SURE, with 100% certainty, the A/C ALWAYS sucks more gas than driving with windows down in the FEH and any "small" engine.

Now, if you have a big block V8 or Triton V10, then the car will hardly notice the A/C.

The A/C takes about 5-6 HP.
So 5 HP out of 100 in a 2.3L Escape is a very large % of the available power. 5 HP out of a "super duty" truck is no big deal.

Using A/C in a Hybrid, any hybrid is a BIG DEAL.
A/C will always REDUCE fuel economy, at ANY speed.
Ford says so, as well as just about every owner.
This has been published by Ford:


Ford says the Escape Hybrid will:
Get 30 MPG at 30 MPH with A/C on. Get 50 MPG at 30 MPH A/C off, windows down. 40% better with windows down at 30 MPH.
Get 25 MPG at 75 MPH with A/C on. Get 27 MPG at 75 MPG A/C off, windows down. 8% better with windows down at 75 MPH.

Its's probably a wash at about 85 MPH!

If possible, roll down the windows instead, in all cars with small engines, and you will $AVE gas.

Don't know where you got your wires crossed Tim!
-John

Back to the OP from Terry... if your Escape is between 8,000 miles and 12,000 miles I have a good idea what probably happened.
Around 10,000 miles, but I have heard of it at 8,000 miles, the HV battery goes through a "recondition" event. That event takes the battery out of service for about 10-15 minutes. If it happens every 10k, I do not know.

 

Compressor capacity is also a function of RPM. I expect there are some points where slower compressor RPM would produce adequate cooling while using less energy.

...electric powered A/C can provide variable capacity cooling!

 

Actually the real numbers are even worse. Although you have a 100HP engine it RARELY operates at that level mostly operates down around 20-30HP, making that 5HP A/C a "honking: ~20% of the load factor.

"Compressor capacity is also a function of RPM."

Yes, and you can be certain sure that the designers, to make up for that shortcoming, gave the compressor enough capacity so it could keep you cool and charming while idling along on a HOT and bright sunny day in stop and go traffic. Which is why it has its own private CLUTCH.

I would imagine tha design capacity is such that the clutch will be engaged almost 100% of the time that the engine is at or near idle for extended periods.

Insofar as FE is concerned could things be any worse...?

Well.....YES.

You could use a compressor driven by the hybrid battery.