Mileage drop in winter

But it does turn on in defrost mode (either defrost only or defrost/floor) above a certain temp (usually around 50 F).

That may be true, but I'm not able to find any temperature limitation on my service CD. This is directly from that CD:

"When DEFROST is selected:

-The air inlet blend door is in the no vacuum position, allowing outside air.

-The defrost blend door is at no vacuum, directing the airflow to the windshield through the defroster ducts and the side windows through the demister ducts.

-The panel airflow door and the footwell airflow door are in the no vacuum position so that most of the incoming air is directed to the windshield defroster hose nozzle. There is also airflow to the side window demister and hose.

-The temperature control knob setting will determine the amount of air that is directed through the heater core and the amount that bypasses the heater core.

-The A/C compressor is enabled when DEFROST is selected to dehumidify the air and reduce windshield fogging.

-The blower motor is on."

The verbiage is pretty much the same for when DEFROST/FLOOR is selected. There are other descriptions throughout the CD about these operations, but they don't list a temp limit either, not even under the Diagnosis and Testing section.

We're supposed to have some colder weather later today and tomorrow. I'll check it out and see if it's running when the ambient temp is less than 50. Or are you saying it needs to be over 50 inside the passenger compartment of the vehicle for the compressor to kick in?

Only because nobody wants to admit having OCD. :-D

Now I'm totally confused. I'll have to check, but it does make sense to switch on the AC for defrost. AC with defrost would clear the windshield much faster than either alone. If it's true, I say thumbs up to Ford engineers. It would also explain part of the mileage drop in the winter, as most of us warm up the car with the defrost on, not thinking the AC is running. At least I'M not thinking the AC is running.

not geared for load carrying, and much better aerodynamics. The escape is like a brick, aerodynamucally speaking.

With an Air conditioned car, the compressor runs any time the defroster is on (air to windsheild) even if split to windsheild and floor.

Been that way for decades.

The A/C isn't running above a certain temperature, usually about 50 F. Air at lower temperatures doesn't hold much water. It's not just Ford, but most other makes that turn the A/C when the car is in defrost or defrost/floor. The reasons for the mileage drop includes lower air pressure in the tires (if you don't; the air pressure drops with the lower temperatures), longer times to warm up the engine (engines run less efficiently when they are cold) and the winter blend of gasoline (which isn't as efficient, either).

Jeff

Not true. If it is in danger of icing up, it cycles the AC off, otherwize it is on.

Not true. Why would a car maker leave the A/C run when it already has the temperature? Air has almost no moisture at 50 F. So most cars that turn on the A/C for defrost also turn it off at 50 F or so.

Jeff

Well we haven't seen 50 degrees here for a month, and probably won't for at least two more months.

BS , Windows never fog on rainy days at 50 deg. ? Oh wait it can't rain at

50 deg. the air has no moisture. Try again sonny boy.

The temp outside this morning was 34 degrees, and inside my Escape, it was

1. I started it up, had my S.O. turn the defrost on while I watched, and sure enough, the compressor clutch engaged, starting the compressor. It did cycle on and off, but was on longer than it was off. I had here bring the RPM's up to about 1500 or so and hold it, and the compressor ran a lot more than it was off. I didn't check the temperature of the air coming out of the vents, and I doubt it was any colder than the outside air, but the compressor was running.

May not have been a scientific study, but the thermometer I use is certified accurate (it's the one I used for work on PC's and server rooms), and was calibrated just over a year ago.

-- SC Tom

IMO the temp coming out of the vents is more a factor of the engine temp and where the temp control is set. I can easily get hot air even if I turn the AC on manually if the temp control is set to hot.

True, but I had the temp knob all the way down. The only engine heat you would be picking up would be from the temperature of the coolant. The temperature knob is not what it used to be on older vehicles. Where those had an adjustable valve on the coolant inlet side of the heater core, the new control just blends the cabin air or outside air with air crossing the heater core or A/C evaporator. A somewhat simpler system, but not as easy to fix if the blend door breaks.

-- SC Tom

No, but the air holds little water at 50 F vs. 80 or 100 F. At 50 F, about 1% of the mass of air can be water (at sea level), but at 80 F,

70, it is nearly 2% and at 84 F, it is about 3%. It goes up faster after about 100 F.

Rain is liquid water, not water vapor.

The amount of water that air can hold at 50 F is a lot less than at 80 or 100 F. There's not that much water vapor that air can hold at 50 F, so there is not much to be gained by removing the moisture from the air. Besides, if you remove much of the moisture, the evaporator will start to ice up.

I don't see the point of cooling the air when it is below 50 F to remove the water vapor if there isn't much water vapor to begin with.

Jeff

The '97 Ford Explorer Owner's Manual states, when discussing the position of the air flow control: "The [defog symbol] directs outside air to flow through the floor vents and the air conditioning compressor will function to dehumidify the windows provided the outside temperature is above 10°C (50°F)." (p30-31)

Obviously, this doesn't apply to all vehicles or all Fords.

[... ]

Somewhere in the 70's, I think foreign cars tended to control the flow of water, and domestic cars controlled the flow of air, with the water flow unrestricted. Now I think they all control the flow of air.

My 2005 Escape Hybrid manual (thanks to Ford for making these available as pdf) says nothing about turning off the compressor at 50 degrees.

" Distributes outside air through the windshield defroster vents and floor vents. The air conditioner will automatically turn on to dehumidify the air. Note: With the climate system set to (defrost/floor) mode, the engine will typically run continuously, reducing fuel economy.

Distributes outside air through the windshield defroster vents. The air conditioner will automatically turn on to dehumidify the air. Note: With the climate system set to (defrost) mode, the engine will typically run continuously, reducing fuel economy. "

At risk of changing the subject, where does Ford make these PDF manuals available?

These go back to 1996.

-- SC Tom