I've often been asked the "AC question" and how to minimize the FE hit of its use in the summer months. This thread is an attempt to leverage the built-in capabilities of the the AC system on the HCH-II not only for driver "comfort" but also to enhance the IPU's thermal management (The IPU is that thing behind the rear seat with an intake vent at the top ). Old dog seeking new tricks As most of us know, using AC will always have some sort of impact on fuel efficiency. Some would say that the smaller the primary power source (ICE) the more significant the FE hit will be and that is definitely NOT far from the truth - particularly on the HCH-II. At first glance many will see this as a biblical truth and for good reason: no matter how we look at AC use, it is a significant loss of energy that will be diverted from your gas tank straight into the thin air. So, what else can we do? Never turn the AC on? Fortunately for us, the answer is not as simple as black & white and it lies instead in the wide range of shades of gray somewhere between those two extremes. Whether we know it or or not, the climate control on the HCH-II is an integral part of the hybrid system and it plays a very significant role in the behavior and relative health of your hybrid specific components. How so? Without getting too technical, let us just say that the IPU really needs to breathe and that many of the components housed in the IPU enclosure have different temperature tolerances that require some form of active thermal management. The primary means of IPU thermal management is quite simple. A fan housed inside the IPU simply draws air from the passenger cabin and channels it through a variety of critical components. The first in the line of this airflow is the battery pack (also the most sensitive) and then all the other modules downstream from it: The BCM, MCM, DC-DC, AC Driver. Obviously, as this "cooler" air flows into and over each component it "warms up" and eventually leaves the IPU though a duct in the right rear of the trunk. Now, to make things really interesting we could take an inexpensive digital thermometer with a remote probe and we could attach it to the outside shell of the IPU after removing the rear seat back (it is actually quite easy to pull out). Better yet would be to have a multichannel thermal probe and stick each probe to each module's housing along the path of the air flow (as it travels through the IPU enclosure). For this you will have to remove the IPU cover (not recommended for the average person - I mean it !!!). You'll be amazed as to "how high" the temperatures can get even with a simple probe setup... and especially if you take into account the individual temperatures thresholds I had published before. Very quickly you'll value the work the IPU fan is doing. But still, the IPU fan can only do so much. In a hot day, the fan will be sucking in VERY hot air during the first 5-10 minutes and guess what that does? Yes, the EV assist affinity grows VERY high (hard to keep the assist off) and the regens are minimized (regens cause heat). At this point the whole IPU may even be dropped into the dreaded managed mode which is often accompanied by an instrumented recalibration (SoC drops to 1 bar and then a force regen takes over for a good while). So what can we do to avoid all these bad things let alone minimize the FE impact? Here are some guidelines acquired from the "collective wisdom fountain": Before driving off, open the windows and/or doors of the vehicle to let the warm air out. The longer the better of course, but depending on how hot, a good minute or two will help a lot. Use window tinting or an effective set of sun shades. In fact, when it comes to the HCH-II there's no such thing as a jumbo shade. Buy and use the biggest you can find, I assure you you will never regret it. I mean it. Drive off with all the windows down and the fan blower on. At this point keep the AC off. As soon we are gathering speed, close the windows and set the climate control to Auto and the temp setting to the highest possible (31C or 88F). Also set face/upper body vents ON and direct the air flow to the head liner. As soon as the blower fan begins to slow down lower the climate control temperature by one degree. The fan will speed up and then slow down again. Keep lowering the temp by one degree at a time until you reach a comfortable temperature setting. You'll notice that the comfort zone temperature is much higher than what most of us would set at first. Whenever possible, turn off the AC outright by pressing the lower right most button until the climate control display reads AC OFF. Now, what does this all do? It forces the hotter/stale air out of the car and prevents it from being sucked into the IPU. It forces the hot air out of climate control ducting before running the cooled AC air through it. It coerces the climate control to run off the electric scroll compressor from the very beginning, thus minimizing the FE hit. By making temp changes gradually the power demand from the AC compressor is also fractional. It keeps the pack cool and happy. Remember, the AC driver will produce a lot of heat if the AC is driven at full tilt so we definitely want to avoid heating the IPU too aggressively when we're supposed to be cooling it. By venting it to the headliner, we are forcing the cooler air to travel along the surface of the roof which allows it to travel further. As cooler air is heavier it will easily reach all occupants and even the IPU vent. Anything else we can do to make it even better? Yes. Minimize the assist whenever possible and use a good number of SoC management techniques available in this forum. Avoid full regen braking at 5 bars or more. In fact, if you can glide while regening at 1-3 bars you'll recover far more energy without over-running the pack with peak heat generation. Anyhow, enjoy the higher FE and stay cool whenever possible... your pack will thank you. If you have any additional tips or comments please don't hesitate to post them... summer does not last for ever, you know.