Hybrider Report post Posted June 20, 2014 Also another point I would like to make is that I see very little difference in cooling efficiencies with doing a semi-manual setting of the fan speed to low, versus setting the climate control to Auto with a high temp setting such as 80°. The fan is still blowing at the same fairly low setting in either case, but the A/C power draw for the manual low-speed fan setting is 1 kW less (1.5 kW vs 2.5 kW) than the Auto setting (temp = 80°), so the manual setting of low fan speed seems to me like a better setting for higher MPGs. Quote Share this post Link to post Share on other sites
acdii Report post Posted June 20, 2014 Understanding what the compressor is doing you need to understand how AC functions. There are 4 components to the AC system that has not changed since the first one was put in a car. Compressor, Condenser, Evaporator, and blower. The compressor sucks the gas from the low side, compresses it into a high pressure gas, the condenser cools the gas so it becomes a liquid, it then goes to an accumulator, or pressure regulator of some sort, this part varies by manufacturer, then to the evaporator. The hot air over the condenser gets absorbed by the low pressure liquid which turns it into a gas, in most cases the "Freon" is a gas as it enters the Evaporator by having its pressure reduced. When a car has reached its set temperature, fan speeds lower, reducing the air flow over the Evaporator, because the air is no longer putting heat into the evaporator, the coolant builds pressure. Its the changing of liquid to gas that occurs in the Evaporator, by heating up the coolant, the liquid under high pressure quickly turns to gas, lowering the pressure on the low side. When the air has cooled down enough that it isnt converting the liquid to gas fast enough to keep pressures low, the low side switch stops the compressor. In a traditional car, this is how it functions, regardless of the type of "Freon" used. R12 or R134, the systems are the same. On the new Electric driven compressors, the flow of coolant is controlled by varying the speed of the compressor. For a hot car, the temperature rise between liquid and gas it very high, so it has to pump the "Freon" at a very high rate. As the air flow over the core decreases in temp, the amount of "Freon" required to cool down or maintain temps is reduced, so the compressor slows down to meet the lack of demand. So the theory of starting with a high temperature of 80* when set to auto, and reducing the temp gradually is going to be the most efficient way to use the climate system because it doesn't have to work as hard to bring the temp down as quickly. This puts less demand on the compressor, Hope this helps to clear this up. 1 hybridbear reacted to this Quote Share this post Link to post Share on other sites