Automotive

Can you run car a/c and heater simultaneously?

  • Last Updated:
  • Sep 26th, 2011 2:30 pm
[OP]
Deal Addict
Sep 27, 2008
2619 posts
273 upvotes

Can you run car a/c and heater simultaneously?

I want to dehumidify the car but still want heat.
32 replies
Jr. Member
Nov 30, 2010
173 posts
14 upvotes
Sure you can run the A/C with heat. It helps to remove the moisture form the air.
[OP]
Deal Addict
Sep 27, 2008
2619 posts
273 upvotes
beleafer81 wrote: Sure you can run the A/C with heat. It helps to remove the moisture form the air.


false. if you turn heat on, you are shutting down the a/c. a/c is temp controlled. a/c doesnt just blast away. if you set the temp for high, the a/c compressor will shut off.
Deal Addict
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Jul 11, 2006
2013 posts
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Toronto
mtseymourguy wrote: false. if you turn heat on, you are shutting down the a/c. a/c is temp controlled. a/c doesnt just blast away. if you set the temp for high, the a/c compressor will shut off.

Wait, you're answering your own thread, OP?
Deal Addict
Apr 22, 2009
1058 posts
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London ON
beleafer81 wrote: Sure you can run the A/C with heat. It helps to remove the moisture form the air.

+1
many dont know that using a/c in the winter is okay and helps defrost windows a little faster
Definition of AIR-CONDITION

transitive verb
: to equip (as a building) with an apparatus for washing air and controlling its humidity and temperature;
To keep your car's compressor in shape throughout the year, it's recommended that you run the A/C compressor regularly, to keep the system working properly and to extend its longevity. Many cars use the A/C compressor for functions of heating and ventilation in the defrost cycle, too. But if your car doesn't, you should run the compressor for at least 10 minutes each month, even during the winter months.
Member
Sep 10, 2006
212 posts
29 upvotes
Vancouver
mtseymourguy wrote: false. if you turn heat on, you are shutting down the a/c. a/c is temp controlled. a/c doesnt just blast away. if you set the temp for high, the a/c compressor will shut off.

Note quite... Depends on the car. On my old car, the A/C would automatically turn on if the outside temperature was > 4C and you set the heating controls to defog the windshield. Whereas my current car has some sort of condensation sensor, and can manually control when the AC is on/off (even if you are heating the cabin)
Deal Fanatic
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Apr 4, 2009
7698 posts
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North York
I thought the A/C automatically turns on whenever you turn on the windshield defogger ... even in the winter time.

In the summer it is easy to tell due to the tell tale A/C condensation dripping from under the engine.

In the winter, I attributed the lousy mileage to the A/C going on when using the defogger on the front windshield. Also, (in winter) when you switch the defogger ON, the windshield clears up REALLY WELL and QUICKLY. In the old days ... blasting the heat on FULL on the windshield was nowhere near as effective.
Deal Guru
Feb 9, 2006
12793 posts
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Brampton
mtseymourguy wrote: false. If you turn heat on, you are shutting down the a/c. A/c is temp controlled. A/c doesnt just blast away. If you set the temp for high, the a/c compressor will shut off.
wtf...
[OP]
Deal Addict
Sep 27, 2008
2619 posts
273 upvotes
Looked it up in owner's manual: Air conditioning comes on automatically if you select "defrost front windows" . a/c also comes on if you select the pic where the arrow points towards your feet. So, you never turn on your a/c and heater simultaneously.

myths in this thread:

1. you have to turn on a/c in the winter to oil seals. (wrong because it comes on auto when you defrost or defog)
Sr. Member
Feb 16, 2009
836 posts
81 upvotes
705
depends on the car. many modern vehicles run the a/c automatically when defrost/defog selected to dehumidify. whether or not the driver is informed of the a/c being on, or whether it is automatic or driver selected is up to whoever designed the hvac controls and strategy
compressor cycles automatically on defrost in my Ford, I have to push the button in my Kia

however, in ambient temps below approx. -25C, the a/c compressor should not come on at all
Deal Guru
Feb 9, 2006
12793 posts
7489 upvotes
Brampton
mtseymourguy wrote: Looked it up in owner's manual: Air conditioning comes on automatically if you select "defrost front windows" . a/c also comes on if you select the pic where the arrow points towards your feet. So, you never turn on your a/c and heater simultaneously.

myths in this thread:

1. you have to turn on a/c in the winter to oil seals. (wrong because it comes on auto when you defrost or defog)
Again WTF... no one mentioned seals...
Deal Addict
User avatar
Nov 18, 2007
3528 posts
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Corktown
mtseymourguy wrote: I want to dehumidify the car but still want heat.
mtseymourguy wrote: false. if you turn heat on, you are shutting down the a/c. a/c is temp controlled. a/c doesnt just blast away. if you set the temp for high, the a/c compressor will shut off.
mtseymourguy wrote: Looked it up in owner's manual: Air conditioning comes on automatically if you select "defrost front windows" . a/c also comes on if you select the pic where the arrow points towards your feet. So, you never turn on your a/c and heater simultaneously.

myths in this thread:

1. you have to turn on a/c in the winter to oil seals. (wrong because it comes on auto when you defrost or defog)
First of all, drinking and posting don't mix. ;)

All of the Honda vehicles that I have owned allowed control of the A/C regardless of temperature selection.

For vehicles that have "climate control" systems, the ability to mix both heat and cool is dependent on the software and may only occur when the user selects "Defrost". In fact my Hyundai Santa Fe, with dual-zone climate control, automatically selects defrost and A/C when it is started on a cold day.
Deal Fanatic
Mar 12, 2010
6092 posts
639 upvotes
SW Ontario
Some vehicles when you put it on defrost the AC light may not come on, but most if not all common modern cars (mainstream vehicles at least), the AC compressor will come on with the defrost or Bi-level split selected. you may be able to push the AC button to light it up, but the AC technically should already be on with defrost. If it's a rainy day and you have vent on and windows are fogging up you can have the temperature selection up higher on any setting and turn on the AC with the AC button to remove moisture from the air.

So to answer the original question, the heater is always running (as it's taking heat from the engine), so if you move the temperature setting to full hot, and turn on the AC you will not ruin anything, just get dryer hot air. Even on a not so hot or cold day, we sometimes have the AC on, but if the sun is down and it's still warm out, then we back off the temperature from full cold to a bit warmer....
Deal Fanatic
Oct 26, 2008
6792 posts
2558 upvotes
BC
mtseymourguy wrote: I want to dehumidify the car but still want heat.

To summarize, there are basically 3 different types of A/C in a car:

1. Fully automatic climate control, where you select a cabin temp. and let it do its thing

2. Manual A/C, where you are in full control

3. Some combination of the above, where for example, hitting the defrost button turns on the A/C as part of the deal whether you want it or not

You need to know what type you have, and how to work it effectively by reading the Owner's Handbook.

In general terms, the answer to the question is, Yes, you can run A/C and heater simultaneously.
Deal Addict
Aug 21, 2009
1330 posts
72 upvotes
Transient
In my old car I would turn the A/C on in the winter when the windows were steamed up.... and watch the steam fade rapidly while hearing/feeling the compressor come on.

OP why do you think your car's manual is written for all cars :facepalm:
Deal Expert
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Jun 12, 2003
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Markham
Yes I can.. it's too bad you think you know better...
ShadowVlican
Deal Fanatic
Apr 20, 2011
7747 posts
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ON
Air conditioning != cold.

It's a heat pump, can provide cold air, or a boost of heat, depending in direction of flow. Removing moisture from the air is a side effect either way.
[OP]
Deal Addict
Sep 27, 2008
2619 posts
273 upvotes
aqnd wrote: Air conditioning != cold.

It's a heat pump, can provide cold air, or a boost of heat, depending in direction of flow. Removing moisture from the air is a side effect either way.


wow. just wow.
Deal Fanatic
Apr 20, 2011
7747 posts
2729 upvotes
ON
Too good for physics are we?

Any air conditioner is a heat pump - moves heat from one place to another. Usually this is one sided(cooling). If set up properly, the heat flow can be reversed to both remove or provide heat.

Thus, the answer for automotive applications depends on how the AC is connected and controlled. If flow is reversible, it will provide extra cooling or extra heating.

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