A/C Power Draw Observations

[Hybrider]

I posted this data as a response to a question I received in the "Fuel Mileage" topic category, but I wanted it to be listed in the "Climate Control" topic category as well, since this is a more appropriate place for this data.

 

Over the course of several days, I have monitored the A/C power draw on the MyView gauge, and the behavior was not at all what I had expected to see.

So to begin with, the A/C power draw data for in the morning when I leave for work, when the temps are in the 85°-93° range in my garage (outside temp is actually around 75°-80°), the A/C power draw climbs immediately to about 2.5 kW, no matter whether I am in complete "Auto" mode or in semi-manual mode or in Max A/C mode. It stays at that initial maximum draw for only about 1-2 minutes, and then over the course of about another 1 minute, it drops to a final level fluctuating between 0.4-0.6 kW, and stays at the same low level for rest of the duration of my 30 minute commute. Even if I change the temp or fan speed or air flow path, there is no effect on the A/C power draw, no matter whether I am at the initial high draw or at the final low draw. This was the surprising part for me.

Now if I change to Max A/C mode after reaching the final low draw (0.4-0.6 kW), there will be no immediate effect on the A/C power draw. But after about 1 minute, the power draw will very gradually start climbing, and after several minutes of this Max A/C mode, when I can no longer stand it anymore due to the excessive noise, air flow, and coolness, it has only increased the power draw by about 1 kW to about 1.5 kW. I don't know if power draw while in Max A/C mode would keep climbing since I am not able to endure the Max A/C mode any longer after I have reached my limits of endurance.

So now for the A/C power draw data for my return trip from work, when the ambient temps are at true desert-level temps. For my drive home from work, when the outside temp is around the 107°-110°, and with my FFH having been parked in the shade, the power draw curve over time is basically the same as I mentioned before, with the max power draw peak being immediately as soon as I turn the A/C on, and the final low power draw being reached a few minutes later. But the difference during these afternoon high temps of the day is that the max initial power draw is about 3.5 kW for about 2-4 minutes, and then the final low draw is slightly higher, fluctuating between 0.6-0.8 kW.

The A/C power draw behavior I saw when I have been parked in the sun at 105° is that the peak draw was around 4.5-5 kW for about 2-4 minutes, and the final low draw was the same 0.6-0.8 kW draw that I saw when I started with my FFH in the sshade.

To reiterate, I basically saw no difference in the power draws that I saw over the course of several days that could be directly attributable to the varying A/C modes that I had selected. The only variable that seemed to affect the A/C power draws, whether it be the initial peak draw or the final leveled-off draw was the temp inside the car, which was directly correlated to the outside temp and whether my FFH was parked in the sun or in the shade. I monitored the A/C power draw while using various climate control settings, including "Auto" mode with various temp settings between 72° and 80°, and including various semi-auto settings, by changing the fan speed, the air distribution settings, along with changing the set temps, and even using Max A/C, and I did not see any immediate change in the A/C power draw when I changed any of those settings. As I mentioned, the only time I did see any change in power draw was when I left the climate control on Max A/C mode for several minutes after reaching the final low levels, and it would only increase by about 1 kW above the final low draw.

Anotber new-to-me observation I have noticed is that there does not seem to be any truly manual mode with my 2014 FFH climate control system since the temp setting is always involved to some degree or another in a semi-auto fashion. Even when the fan is set to a manual, user-specified speed and the air distribution setting is set to a manual, user-specified air vent selection. I have not found any way to not have the temp setting involved in some way, since it always seems to change the output air temp to its own volition.

So here is a table summarizing the A/C power draw data, for desert ambient temps, that I have detailed above.

Initial Park Condition and Ambient Temp
---------------------------------------------
Shade, 85°-93° Shade, 107°-110° Sun, 105°
-------------- ---------------- -----------
Initial Peak Draw 2.5 kW 3.5 kW 4.5-5 kW
Duration of Peak Draw 1-2 minutes 2-4 minutes 2-4 minutes
Final Draw 0.4-0.6 kW 0.6-0.8 kW 0.6-0.8 kW

So based on my findings and comments from others in this forum, my BKM (Best-Known Method) that I use now is that I start my summer desert trips in Auto mode, with an initial temp setting of 80°, and then when I start feeling too warm due to the decreasing air temps being output through the mid-level dash vents, I will then drop the temp setting by about 1-2° at a time, which usually eventually ends up stablilizing on a setting in the 74°-76° range. Then, at my final selected auto temp settiing, if my eyes start getting too dried out from the air coming out of the mid-level dash vents, located on either side of the steering wheel which I always leave positioned directly at my face, then I switch the air distribution to be dash vents (middle level) and defrost vents (upper level), thereby being a semi-auto setting.

 

And then I rinse and repeat at the beginning of the next day.

[Easy Rider]

Just the facts man.

Thank you for an excellent post. :thumbsup:

 

Now.......if some engineer type could translate that .8 KW max. ongoing draw into fuel use for us.......... :)

[larryh]

You can easily estimate the amount of fuel used by the A/C. Assuming the ICE is about 34% efficient, the generator is 80% efficient, and there is 33.705 kWh of energy released per gallon of gasoline, each gallon of gasoline will provide 9.2 kWh of electricity to run the A/C and other accessories. So if the A/C uses 0.8 kW of power, that is 0.09 gallons of gas per hour.

[Waldo]

We need more precision to draw any conclusions from this. The "duration of peak draw" is very critical. The range of time in your chart varies by 100% which is enough to swing the conclusions from one side to the other. For example drawing 4.5kW for 2 minutes will draw less energy than 3.5kW for 3 minutes.

[larryh]

Below is a plot of power consumed by Climate Control for a short 13 minute trip when A/C is set to 78 F and the outside temperature is 82 F. I have a Fusion Energi, which has an electric heater. The electric heater came on one minute into the trip, so both the heater and A/C were running for most of the trip. The A/C consumed 0.12 kWh of power during the trip. The heater also consumed 0.12 kWh of power. The total energy usage for the 13 minute trip by climate control was 0.24 kWh.

 

 

Edited June 20, 2014 by larryh

[hybridbear]

Here's a question: what if the dash display isn't accurate?

 

Larry & I have found that using the compressor amps times compressor volts as reported by the car does not give a reading that matches the dash graph. He adjusted for this by creating a new PID which approximates compressor amps based on other data points. Now the A/C Power formula closely matches the dash display. But, what if the dash display is wrong? What if the actual A/C power consumption is the result of multiplying what the car reports for A/C amps & volts? I have not personally looked through FORScan to see if there is a PID to display the kW that the car is using to run the dash graph, but I bet there is one. I'd be interested to compare that result with what the car reports for amps & volts to try to figure out where the disconnect is.

[Hybrider]

Below is a plot of power consumed by Climate Control for a short 13 minute trip when A/C is set to 78 F and the outside temperature is 82 F. I have a Fusion Energi, which has an electric heater. The electric heater came on one minute into the trip, so both the heater and A/C were running for most of the trip. The A/C consumed 0.12 kWh of power during the trip. The heater also consumed 0.12 kWh of power. The total energy usage for the 13 minute trip by climate control was 0.24 kWh.

 

 

This is the plot exactly as I observed and described :) , but with differing peak levels, final leveled-off levels, and time durations before the leveling off; all of which were based on the difference between the temps inside my car and the set temp on the climate control.

Edited June 21, 2014 by Hybrider

[Ram]

I have noticed that about 30 to 40 min's of idling in traffic jams can reduce miles for life by .1 while running the A/C. I have also had the radio on and figure that is nominal draw and almost not measurable with out additional equipment attached to both of the batteries.

[acdii]

There is a TSB for the Climate programming. You CAN turn off the AC compressor when you touch the AC switch. WOOHOO.

[srogers]

There is a TSB for the Climate programming. You CAN turn off the AC compressor when you touch the AC switch. WOOHOO.

That's great news. It's one of the few things I don't like about my Fusion. Do you know the number that has been assigned this TSB?

[hybridbear]

There is a TSB for the Climate programming. You CAN turn off the AC compressor when you touch the AC switch. WOOHOO.

I will second the srogers request for the TSB number & PDF if you have it. It should be posted in the TSBs section.

[acdii]

I will see if it is on the paperwork.

[Easy Rider]

That's great news. It's one of the few things I don't like about my Fusion. Do you know the number that has been assigned this TSB?

 

Admittedly I can be a little dense sometimes but I don't understand why this is such a big concern.

 

It does not keep the compressor running unless it thinks it needs it for dehumidification.........right ??

 

When I turn the AC off (or think I am) but leave the fan running in my '14, it gets hot and humid pretty quickly.

[FrankQC]

When I turn the AC off (or think I am) but leave the fan running in my '14, it gets hot and humid pretty quickly.

Same thing for me with my '13, but only if it is not in [AUTO] mode. As soon as this AUTO mode is engaged, the compressor keeps running all the time, even if my AC button is off and the temp setting is far from requesting AC... Looks like the AUTO mode keeps the air flowing through the front defrost vents, thus starting the AC compressor, whatever the AC is requested or not.

 

I really like the air flowing through the three possible outputs (including the defrost vents) but would like to get rid if the running compressor when I do not want it or need it to defrost my front window. Moreover, that compressor / fan combo is as noisy as a running ICE :-(

[murphy]

I really like the air flowing through the three possible outputs (including the defrost vents) but would like to get rid if the running compressor when I do not want it or need it to defrost my front window. Moreover, that compressor / fan combo is as noisy as a running ICE :-(

Press buttons in the following order

MAX A/C

A/C

Recirculate

Adjust fan speed to what you want

Select the vent you want to use.

[FrankQC]

Press buttons in the following order

MAX A/C

A/C

Recirculate

Adjust fan speed to what you want

Select the vent you want to use.

I just went outside and tried it, doesn't work. As soon as there is air flowing through the defrost vent, the AC compressor starts. There is no way to select the defrost vent manually (even along the other two vents) without the compressor starting. (At least on mine) the AC button is Off but the compressor still runs.

[murphy]

Do not select the defrost vent. That forces the compressor on to provide dehumidified air.

[FrankQC]

Do not select the defrost vent. That forces the compressor on to provide dehumidified air.

Yup, that is exactly what my post was about... On my two other cars, if I select the defrost vent, I see the AC light turn on (which is normal) but I can turn it off manually, keeping the air flowing through the defrost vent without the AC running. On the FFH, the AC compressor keeps running in defrost mode even if the AC light is off. That's what bothers me.

 

Anyway, thanks for the reply, I'll stop posting about this as I do not want to highjack this thread any longer.

[acdii]

TSB number wasn't listed on the paperwork :(. I will need to see if the AC can now be turned off while on defrost, which is my biggest complaint.

[James Sentman]

I dont think the MaxAC setting changes anything as to how much power is being used buy the compressor. I think it’s just a preset for, recirc, lowest temp setting and high fan speed. It’s there to preserve your regular climate settings so that you don’t have to hold the temp down button for 20 seconds to get it to scroll all the way down to Lo and then hit the fan up button half a dozen times and then hit the recirc button and then have to undo all those things when you want to go back to regular temp management. As a one hit preset for those settings I think it’s a great idea. but it doesn’t seem to magically make the AC colder or force the compressor to work harder than it would if you did those other things.

[larryh]

The only time that have observed the AC using 5 kW of power is when climate is set to Max AC. I have not observed that much power draw when set to normal AC. 5 kW of power seems excessive--that is more than the central AC in my house uses and that has to cool a lot more air.

[Hybrider]

As I noted in my original post in this topic, I have personally seen up to 5kW power being drawn by climate control when my car was parked in the direct mid-day sun with temps at 105°. And I was not using the Max AC mode, since I never use it due to the FFH climate control already being so effective for me without me having to use it.

 

From my observations in a desert clime, the initial A/C power draw has no dependence on the climate control settings I use, but only depends on the temp difference between the temp inside the car versus what my desired temp is. The desired temp setting is basically irrelevant for me too here in the desert since when a sealed car is parked in the direct sun in 105°-115° temps, the inside temp easily reaches 160°. The reason I say the climate control temp setting is "irrelevant" to me is that in the FFH a climate control setting of 72° vs say 82° is so much lower when compared to the inside temp of 160° that the computer will apply max A/C for either desired setting to try to bring the temp down, no matter what the desired temp setting is set to.

 

So I have found that using the "Auto" setting works for me no matter what the temps are, since the FFH computers know when I really need the max A/C to be cranked up, and when I don't. But I do start out with the temp setting set to 82° to try to minimize the time the compressor is at that peak power draw level, and then once the A/C power draw has decreased to its lower, static level and the A/C starts blowing warmer air, I then start decreasing the desired temp setting, initially by 2° at a time, and then as I start to get close to my final desired setting, by 1° at a time.

 

It is interesting to me that my final desired temp in the cooler morning temps can be as low as 72°, but in the afternoon heat-of-the-day, my final desired setting is usually more like 74°-75°. I figure this is due to the fact that the computer seems to want to blow cooler air at me when the temp delta between outside and inside desired temps is greater during the hottest temps of the day. So IOW, the air-flow temp I like to feel on my face is about the same either time of day, but in the morning an outside temp of 90° vs the 72° desired setting is a delta of 18° which is still much less of a delta then when the outside temp is 110° vs my 75° desired setting, creating a much larger delta of 35°. So the A/C will still be trying to compensate more during the hottest part of the day even though I have a higher desired temp setting (75° vs 72°) and therefore will blow colder, or at least as cold, temps at a higher desired setting.

 

These FFH computers are so cool! (pun not really intended, but I'll take it) ;)