I think what you want is control over the hysteresis -- right?


Brian

 

if you hit the AC button, it will stay off until you either shut off your car and start it again, power cycle the climate control, or hit the auto button and the car thinks it needs it on.

But turning the AC off will leave it off for the durration of your trip.

 

Brian,

I had to look up what that refers to, and if I understand you correctly that has to do with a memory or lag. That's not really what I meant -- I think I may not have described my issue very well.

I can understand why "Auto" would have the vehicle warms or cools the car inkeeping with your target temp. But regardless of whether it's set to Auto or not, what do I do if I am happy with a temp ranging from 65-80 fahrenheit, for instance? For simplicity's sake, I just want it no hotter than 80. I don't need it to cool me to 78, then heat me to 80, then cool me to 78, and so on.

All I want is cooling and I can't disable heat. And in Winter, I'ms ure the opposite will be true.

I hope that clarifies. Sorry, I'm not very good at explaining.

Thanks!

 

Quoting from Wikipedia ...

"Many artificial systems are designed to have hysteresis: for example, in thermostats and Schmitt triggers, hysteresis is produced by positive feedback to avoid unwanted rapid switching."


Brian

 

I think you might be mistaking ambient temp air from the vents as heated air from the vents.

In my experience, on Auto, as the temp reaches the set point, the fan slows, and the air is cooled less and is closer to ambient temp. The system never "stops" like a home A/C would, so it compensates by adjusting the temp of the air from the vents to maintain a constant temp in the cabin. If the temperature rises it starts to cool the air more.

 

just take it off auto

 

I have never noticed the Auto climate go back and forth between heating and cooling. As others described, it should stabilize towards your target temperature and become pretty steady at that.

Using the Auto function on mine has the AC compressor on pretty much all the time, no matter the temperature outside.

 

Thanks so much for chiming in, you guys -- it's really helpful.

Brian, I definitely see now how "hysteresis" relates to the problem. Essentially, it is the automatic switching of cooling/ heat to regulate temp -- with potential to overcompensate, creating its own closed loop, back and forth in perpetuity.

Pendarus, you make a very interesting point, too. As you suspected, I'm thinking of it exactly as my home HVAC controls. I didn't think of it as an air mixing mechanism so much as an off/ on one, so that may in fact be part of my issue. Plus, as I'm in Texas, outside air tends to be indistinguishable from warmed air, so that could be what I'm misinterpreting.

Altis, I'm starting to wonder if perhaps my little FoFo (who's been reprogrammed a few times and did have a "leaky compressor" fixed early on) may have a programming issue that causes its "acceptable temp range" to be too narrow.

I think I also just miss the more user-friendly system of my old Acura that allowed for the independent enabling of cooling and heating power.

Thanks, guys. If anyone else has complaints/ concerns/ confusion about the dual Zone system, I'd love them to keep adding to this thread, too. The manual isn't very clear.

 

I'm not sure it's good to think of it as "enabling" cooling and heating... only the AC compressor can be enabled, the rest is just mixing hot and cold air together.

The reason a house thermostat requires you to pick whether you'd like it to heat or cool is because they each operate a separate and independent system. If you set your house heat to 70, it might kick in at 68 and warm to 72, then switch off until the temperature drops again. Same idea with AC.

In the car, though, it's just mixing hot and cold air. If the air from outside isn't cool enough, then it will use the AC compressor (although like I say, mine seems to be on all the time). If you set it to 70 and it's 40 outside, it will put on lots of heat to warm it up (around 80 degree air, for example). Let's say around 65, it starts to level off, and it's blowing air a bit slower and only about 75 degrees. Then it reaches 70, and it's leveled off... it might blow air that's around 71 or 72 degrees to fight the thermal losses, but it should remain around there. If the temperature drops to 67 degrees, it should only add a bit more heat to counter it... not go nuts on full heat until it reaches 70 again.

I suppose the moral is that the intensity which it tries to reach the set temperature is proportional to the difference between the set and current temperatures... You shouldn't seen it try hard to cool at 71 and try hard to heat at 69 if you set the climate to 70. It should be extremely subtle.

I hope this helps to explain, FordFocursing... I'm not brilliant at explaining things though.

 

Don't know if this has anything to do with the behavior you are seeing FordFocursing but I thought I'd throw it out there as maybe it is worth a try. Mine was behaving oddly when I first got the car and someone else on here (csvt I believe) helped me out.

The "Auto" setting is somewhat weird (at least in my car). If you set it to auto, make any sort of change that knocks it out of auto and then try and reactivate auto it doesn't behave as it did before (in my case it kept saying "AC On" no matter how cold it was outside and I, like you, assumed that even with heat coming out of the vents it meant it was "conditioning" the air). Even shutting it off and turning it back on didn't stop this. The solution was to shut it off and turn it back on by hitting "Auto" instead of the On/Off button. After I did this I noticed for the first time the next morning (it was cold) it said "AC Off" when I started the car. Like it totally cleared any overrides or anything.

Again, not sure if it would help but might be worth a try.

 

I would go out on a limb that no one at Ford ever thought 80 degrees would be a temperature that someone would set when they were attempting to be cooled. This would lead to the programming assuming you actually want to be warmed and instead of a < 80 parameter as you wanted, it actually thinks you want > 80. Just my thought as I had to read your OP twice to understand that you actually wanted your cooling temperature to be 80

 

Most modern HVAC systems use a sequential coil setup, cold then hot. This allows for humidity control when the outdoor air or an internal source is causing fog/etc. These kinds of systems have three modes of operation:

1) Heating cool outdoor air with a flow control valve on the glycol from the engine.
2) Cooling outdoor air with a duty cycle on the AC compressor
3) Cooling and then reheating outdoor air for humidity control

Under 1 & 3 it's very easy to set the supply air temperature (to the cabin). All you have to do is incrementally tweak the flow thru the heat exchanger. Under 2, however, it is quite difficult to control supply air precisely. The gas in the phase change cooling system has set pressures and temperature that it operates at. It's an on or off kind of thing, usually, but the Focus might have something a little more precise, I'm not sure. In a less efficient system, you'd just operate under 3 instead of 2 and then the compressor would cycle based on the coil pressure, ensuring that the coil remained at a constant temperature and the heater controlled the desired supply temperature. Under 2 the only option is to cycle the AC compressor so that the mean temperature of the coil is the desired setting instead of instantaneous. It goes cold and then eases back up to warm. The only problem with this approach is that the humidity swings a lot more in the supply air, and that causes the air to feel a lot warmer than it is. The coil can get damp when it cools and then when it stops cooling, all that moisture gets pumped back into the supply air.

There is one more thing to consider: the control setpoint. In a traditional car system, you set supply air temperature yourself. In a household system, the thermostat is in some fixed location monitoring the air. In an always-on/industrial system, the return air duct temperature is monitored. I'm not exactly sure what the focus's system monitors, but I don't think it's supply air since the system runs all out when it's hot in the car. I wouldn't be surprised if the outdoor air temp was used to guesstimate a cooling/heating temp and that parking in the shade causes the sensor to cool down, and thus think it needs to supply slightly warmer air.

 

I'm not exactly sure what the focus's system monitors, but I don't think it's supply air since the system runs all out when it's hot in the car. I wouldn't be surprised if the outdoor air temp was used to guesstimate a cooling/heating temp and that parking in the shade causes the sensor to cool down, and thus think it needs to supply slightly warmer air.

Actually Ford's DATC (dual zone automatic temperature control) system is quite advanced in all their vehicles including the Focus.

It uses the sunload/autolamp sensor in the center of the dash near the windshield to know how much sun is entering the car.

It uses the outside ambient temperature to estimate the air coming into the fresh air inlet.

It has an exit air temperature sensor at the left/right panel and floor vent locations (total of 4)

Lastly, on the lower driver's knee panel below the steering wheel on the right side, there is a cabin temperature sensor. It uses an asperiator system that creates vacuum off the hvac fan to pull cabin air through it to sense both cabin air temperature and humidity.

 

One way to get the operation you want (which isn't typical because I use AUTO all the time, but usually a more normal temp of 68-72).

If you want only cooling, set the temperature control all the way down until it displays "LO". Then override the fan to the speed that satisfies the cooling you need.

The same for heating. Set the temp to "HI" and override the fan speed.

Basically in this scenario you will get a manual control which it seems like you are looking for.

 

Ok, I'm taking detailed noted of the theories and info provided here, thanks!

Csvt2060 brings up a fascinating wrinkle! It doesn't seem that my SEL has Daytime Running Lights, so ... a couple of months ago I put a little bean bag over the dash eyeball to force behavior like DRL (via making FoFo think it's always dark). It never occurred to me that anything climate-control related would be light-sensitive. Interesting!

Ok, so the cyclops eye patch needs to go. I've read on the forums that you can have the dealer program to disable DRL, but having the option in the first place is a feature I had to have added-on, correct? I only added on the 300A Rapid Spec, Interior Protection, and Keyless Entry.

Thanks!

 

Yep, that could be your problem!

The DRL function can be turned on by the dealer through their IDS system.

They will probably charge you an hourly rate for this.