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Discussion Starter #1
This question has probably been asked before but... is the a/c always on whether heating or cooling the car? I am used to a system that allows heat without a/c.
 

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oldfox said:
This question has probably been asked before but... is the a/c always on whether heating or cooling the car? I am used to a system that allows heat without a/c.
A/C only on for cooling or defoging
 

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AC is short for air conditioning.
you can run it for heating or cooling.
it is used to dehumidify the air.
(it is automatically run if you use the front windshield defroster/defogger.)

On the 2004 Prius, if you choose the "Auto" setting, it always uses the AC...
 

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mrv said:
AC is short for air conditioning.
you can run it for heating or cooling.
it is used to dehumidify the air.
(it is automatically run if you use the front windshield defroster/defogger.)

On the 2004 Prius, if you choose the "Auto" setting, it always uses the AC...
I assumed that Oldfox was referring to the cooling compressor. If the Prius used a heat pump A/C system the compressor would then be used for heating and cooling. Since this is not a heat pump system the compressor is only working when cooling or defogging.
 

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you can dehumidify whether you are
asking for heat in the cabin, or
cold air in the cabin.

since the AC button is used for (quoting
from my 2001 owner's manual, p.133)
"powerful cooling and dehumidifying"

besides, the temp setting for 65F
may be heating in the winter, cooling in
the summer. There is no way to
request "heat" or "cooling" by
itself, just a temperature in the
cabin (that's relative to the sunlight
and temperature outside).

(I will note, however, on p.135-136,
under operating tips, the AC button
is suggested to be off for heating,
ventilation, or defrosting the
outside of the windshield, but the
AC button should be on for "Air
Conditioning" and set at MAX for
defogging the inside of the windshield.)
 

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Michelle, I thought we were talking about an 04! But anyway I also have an 03. On the 03 if you don't have the A/C button in the "ON" setting you can get heat only just by setting the "temperature" control to a higher temperature then the outside temperature and as long as you don't use the MAX fan setting.
 

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Discussion Starter #8
Computer problems have kept me from responding (New Motherboard)

Appreciate your comments but am still a bit confused. I have a 2004. If I read your replies correctly, The A/C is always on when in auto mode but must be turned on if in manual? In other words, I can heat the car without A/C as long as it is in manual mode?

If above is true, i wonder why Toyota would do this (Always have A/c on in auto mode) Isn't the A/C a drain on batteries?
 

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oldfox said:
Computer problems have kept me from responding (New Motherboard)

Appreciate your comments but am still a bit confused. I have a 2004. If I read your replies correctly, The A/C is always on when in auto mode but must be turned on if in manual? In other words, I can heat the car without A/C as long as it is in manual mode?

If above is true, i wonder why Toyota would do this (Always have A/c on in auto mode) Isn't the A/C a drain on batteries?
Oldfox, your A/C compressor will not come on in "auto" mode unless you have set the temprature low enough to require cooling.
 

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If you press the "auto" switch, the AC compressor motor is running whether the connected compressor is cooling or not. It can be used to de-humidify if needed. I think most modern cars will not actually turn the compresser on below a certain temperature, but that's a guess from other cars I have owned.

After pressing "auto" you can press the AC switch to turn that motor off. It should reduce pull on the electrical system, I don't know by how much. The owner's manual (at least the version I have) has this information. It says that milage will be improved in this condition.
 

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TCBRT said:
If you press the "auto" switch, the AC compressor motor is running whether the connected compressor is cooling or not. It can be used to de-humidify if needed.
TCBRT, I am confused by that statement and can not find that information in my manual! Could you explain how a cooling compressor could be on and not cooling? By the way, dehumidifying is a product of cooling. You must cool air in order to condens the moisture out of the air. If windshield defogging (dehumidifying) is needed in cold weather, both the cooling compressor and the heat are on together. The compressor is on to dehumidify (and it has to cool to dehumidify) and the heat is on to offset the cooling effect from the cooling compressor! Kind of like Nixon having the fireplace going in the summer and using the air conditioning to keep the house cool at the same time!
 
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