Quote:
Originally Posted by wwest
Your turned the A/C on..??
Now the ICE must provide HOT coolant for the HVAC's reheat/remix cycle after the A/C cools the airflow down to near freezing.
You can improve the efficiency of the A/C (and thereby FE) quite dramatically by running it in MAX COOL mode and then using the blower speed manually to regulate the cabin comfort level. It wouldn't hurt to purchase and install a water flow shutoff valve at Home Depot to stop the flow of HOT coolant to the heater core.
The ICE will still run occasionally to keep the coolant (and catalyst) hot but not as often with the shutoff closed.
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Your A/C settings suggestion is appropriate for typical AC systems found on typical vehicles.
However, the Toyota Hybrid AC system is somewhat unconventional and more efficient than systems on conventional vehicles. The AC compressor is run by a computer controlled variable speed electric motor which runs at the most efficient speed to bring the evaporator coil up to the proper temperature for cooling and dehumidification (below the dew point) at the selected temperature and fan speed.
In a conventional A/C system, the A/C compressor is run off the engine by a fan belt so it's speed is controlled by the engine speed which is not at all ideal - low speed when sitting in sweltering traffic and high speed when it is not needed cruising at 70 miles per hour.
With the Hybrid A/C system, hot air from the heater core is not used indiscriminately and wastefully for modulating the air temperature as on a typical A/C system where the heater and A/C run at the same time for blending air temperature in the A/C mode.
Heat is only used in cases where the ambient air temperature is on the cool side and very humid. If left in auto under this cool and humid condition, the A/C will operate on a very low compressor speed and fan speed to get the evaporator below the dew point for moisture removal. However if this still cools the cabin air too much, a bit of heat from the heater core will be added to maintain cabin temperature.
Under these cooler conditions where you don't want this dehumidification feature, you can just turn off the A/C if you want to maximize efficiency over comfort.