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  1. #1
    Junior Member
    Join Date
    Apr 2008
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    0

    Does Heat Need AC To Be On?

    Driving an '08 and I can't seem to find in the manual whether or not I should have AC on when I use the heat. By default the AC seems to go on when I start the heat, but heat also works without the AC. What's the answer? Thanks in advance.

    Jay

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  3. #2
    Guest

    My exact same question for

    My exact same question for my 07. Today was 32 degrees F and we drove 80miles into a stiff headwind and periodically the air flow felt cold. Temp was set at 68 and the blower at medium. Suddenly the thing went cold. Is this typical or some bad news symptom? On the return trip we played with the thing most of the way home and came to no conclusion. We were warm most of the way, had a chill every once and a while, but it was so irratic there seemed to be no pattern. And the manuel gives no clue. Read the whole thing tonight looking for info and finally under AC stuff came up with some info, but no real answer to the hot/cold switching of the air temp.


  4. #3
    Junior Member
    Join Date
    Dec 2007
    Posts
    0

    The "AC" should really be

    The "AC" should really be labled "HVAC" for Heating/Ventilation/Air Conditioning.

    It's an all-in one system. The car knows when you want heat or cold, by the difference between the outside air temp and the temperature you set. Ask for 68 degrees, when outside air is 30 degrees, you get heat. Ask for 68 degrees when the outside air is 92 degrees, you get AC cooling.

    IF you have the fan set to manually remain in the "medium" position, then it will feel hot and cold as the thermostat kicks in and out. You ask for 68 degrees, and the car shuts of the heat when it gets to 68 degrees, and blows cool air at you.

    Try leaving the HVAC in the "AC Auto" position. The car turns the fan up and down in speed depending on how much heat or cooling is needed to maintain the temperature you ask for.

    As the car cabin approachs the temperature you set (68 deg?) the fan turns down to provide less heat, and try to maintain a steady temperature.

    Note: if you ask for the front windshield defroster (the orange fan-shaped logo), then the car leaves the fan running at a faster speed to keep the windshield from fogging up, and turns off the heat as needed. But the airs blowing on the windshield, not your face, so you don't feel the cold air as much.

    Also note: when you are in "defroster" mode the AC cooling is SHUT OFF to prevent condensation on the windshield from the cold air coming from the AC unit.

    If you set the temp all the way to the end of the scale (HI or LOW) then you get full time, high power fan, heat or cooling regardless of outside temperature or cabin temperature.

  5. #4
    Guest

    The reason the Auto mode

    The reason the Auto mode turns on the A/C with a defroster/heat setting is to remove the condensation in the cabin air that would otherwise cause windows to steam up and/or frost over. Warm air from the cabin moving over the cool coils in your dashboard causes condensation of the moisture out of the air which then drips to the ground. However, you can often turn the A/C off after hitting auto mode with satisfactory results and gas savings.

  6. #5
    Guest

    Direct answer...yes, A/C has

    Direct answer...yes, A/C has to be on while using heating because A/C is what dries the air out. If you have heat alone, the humidity inside the vehicle would become unbearable after a short while….this applies for all vehicles, not only Hybrids.

  7. #6
    Guest

    Direct answer...yes, A/C has

    Direct answer...yes, A/C has to be on while using heating because A/C is what dries the air out. If you have heat alone, the humidity inside the vehicle would become unbearable after a short while….this applies for all vehicles, not only Hybrids.

  8. #7
    Junior Member
    Join Date
    May 2009
    Posts
    0

    I've had cars where having

    I've had cars where having the A/C on with the heater and defroster helped substantially and other cars where it didn't matter. My Nissan Sentra was the worst for fogging up.

    My prius doesn't seem to be that bad for it. I generally turn the A/C off when I kick on the defroster and I haven't had any issues.

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