Have noticed when driving in high heat environments (Phoenix, Sacramento, Palm Springs) that the mileage on the FEH decreases dramatically.

The driving style is, at the speed limit with air conditioning on. The mileage decreases usually about 3 mpg using the same driving style as in cooler environments (going to San Diego).

Just got back from Phoenix (115 degress) and the FEH seemed very sluggish in the heat.

AC is running more often to cool the battery.

And higher outside temps makes the passenger compartment AC work harder to keep you cool.

My 4WD
Wife's 4WD

I have noticed that the mileage is a little lower in the real extreme heat. I have not noticed any loss in performance in the heat although what would make a difference is the air density, or density altitude. A real hot day in Phoenix (1,000' above sea level) could feel like 2000' or much more to your engine. Higher altitudes can really decrease performance.

What I have found that helps when using the a/c is to use the max a/c or recirc mode. This keeps the outside air out and lets the a/c compressor work less because you are only cooling already cool air. This will help your mileage some versus using the vented setting on the a/c.

Just remember to leave the knob set in one of the vented positions and/or leave some windows cracked when you park or you will have one hot car when you get back....

It gets pretty hot here in N. Va (its the humidity). I think the A/C does not work "harder" no matter what the conditions are. These things do not have thermostats like your home A/C. You are the controller of the temp with the knobs. When you turn it on it just works at its rated capacity until you turn it off. When you dial in the temp knob to adjust the cabin temp, all you are doing is just letting in more outside air to dilute the cold air from the unit. The unit is still working at its same capacity, you are just diluting its output. It does not cycle on/off unless you turn it off. In the Max A/C mode, you are just recylcing inside air and boosting the fan, cooling things faster until you find it too cold and go back to the regular mode. In regular mode, if you come to a stop light it turns off and the car can warm up quickly on a hot day. In a really hot climate, it may take longer to cool the car, but it will work at the same rate and burn the same gas as in a cooler climate.

These are just my feelings after having driven A/C cars for a while, but none of them had temp controls, so I may be wrong about those cars with them. I have not noticed huge mileage difference between A/C and non-A/C mode. I sure would not want to spend much time in a non-A/C car in the 90/90 days we have here (percent humidity/temp).

Dave

I would have thought the same thing except several of the Fords I have owned have said in the owners manual that gas milage would be better in recirc mode (MAX A/C) than in vented mode. It said that MAX A/C would cause more noise and possibly cause the windows to fog.

I don't remember what the Escape manual says but I will look into it......

A couple of things are going on here that have an effect.

1. Modern automotive AC systems use a pressure-sensing device to turn the compressor on and off. Since the pressures are related to the load on the system, they do in fact have a "duty cycle" proportional to the heat load on the system.

2. The Escape does not have a thermostatic control for the AC in the passenger compartment. The temperature control on the instrument panel simply adjusts the blend door which allows varying amounts of air to go through the heater core.

3. There is a thermostat for the battery pack, however. The system will bring up the AC to cool the battery if the computer decides the battery is too warm. It'll do this under any conditions, regardless of the settings on the climate control panel.

Another consideration is that while you can use recirc to keep cooler air in the passenger compartment, the ventilation for the battery pack is always outside air.

Since GreenHybrid is a source for real-world data from actual hybrid drivers, think it is appropriate to report trips that shows how heat/AC effects fuel economy. Sure others take similar trips that could report as well.

I drove from Ventura to San Diego in ~90° degree heat with AC recycle on, family of 4 and our two Dalmatians, where I got 31.5MPG. Drove back at night with same vehicle load, but driving in cooler temperatures without AC resulted in 34MPG. Also, on the way down I was driving an average of 65MPG (even in 70MPH zones) but on the way back I averaged 70MPH. Based on this, seems like AC use (for cabin and battery pack) drops FEH fuel efficiency by 2.5MPG or more considering speed difference. Also the heat probably increased tire rolling resistance, but I had my tires inflated to 44psi (max cold pressure rating).

-Dan

What is the altitude of San Diego versus Ventura?

What were the prevailing winds?

My point is that you can't get an accurate comparison by looking at only one leg of a round trip. You'd have to repeat the entire trip under identical conditions to be able to isolate the one variable.

That's not to say that using AC has no effect on fuel consumption, of course it does. But there are so many variables in regular driving that it'd be very difficult to isolate just one. That's why the EPA test is synthetic, it allows them control of all the variables.