# AC and Heat **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** toyota, 4runner\ **Created:** [October 28, 2017, 10:41pm UTC](https://community.cartalk.com/t/ac-and-heat/109000 "2017-10-28T22:41:25Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Tarheel50](https://avatars.discourse-cdn.com/v4/letter/t/9f8e36/32.png) [@Tarheel50](https://community.cartalk.com/u/Tarheel50)\ **Post date:** [October 28, 2017, 10:41pm UTC](https://community.cartalk.com/t/ac-and-heat/109000/1 "2017-10-28T22:41:25Z")
Will running the AC unit while having the heat on in my car damage my compressor in any way? ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [October 28, 2017, 10:43pm UTC](https://community.cartalk.com/t/ac-and-heat/109000/2 "2017-10-28T22:43:49Z")
No. Tester ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [October 28, 2017, 10:54pm UTC](https://community.cartalk.com/t/ac-and-heat/109000/3 "2017-10-28T22:54:45Z")
> [@Tarheel50](#): > > Will running the AC unit while having the heat on in my car damage my compressor in any way? No Is there a particular reason for your question? ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [October 28, 2017, 11:16pm UTC](https://community.cartalk.com/t/ac-and-heat/109000/4 "2017-10-28T23:16:12Z")
Not directly, but it will cause the compressor to engage more time than would be required without the heat being on. For the most part with any mechanical mechanism, more use means earlier failure. ---
**Author:** ![VOLVO-V70](https://avatars.discourse-cdn.com/v4/letter/v/8e8cbc/32.png) [@VOLVO-V70](https://community.cartalk.com/u/VOLVO-V70)\ **Post date:** [October 29, 2017, 12:52am UTC](https://community.cartalk.com/t/ac-and-heat/109000/5 "2017-10-29T00:52:21Z")
Are you being confused by the AC light being on while you are trying to keep warm. The modern cars will run the AC to keep the windows from fogging up. If you have auto temp just set the temp you want and forget it. Like DB asks what prompted the question. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [October 29, 2017, 12:56am UTC](https://community.cartalk.com/t/ac-and-heat/109000/6 "2017-10-29T00:56:13Z")
> [@VOLVO\_V70](#): > > Are you being confused by the AC light being on while you are trying to keep warm. The modern cars will run the AC to keep the windows from fogging up. Yup. In addition to removing heat, air conditioning removes moisture from the air. So modern cars use it to do so. Drier air coming out of the defrost vents better removes condensation from the windshield. ---
**Author:** ![GorehamJ](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/gorehamj/32/24103_2.png) [@GorehamJ](https://community.cartalk.com/u/GorehamJ)\ **Post date:** [October 30, 2017, 2:11pm UTC](https://community.cartalk.com/t/ac-and-heat/109000/7 "2017-10-30T14:11:56Z")
No, it is a common way to defrost the windshield in certain weather conditions. ---
**Author:** ![Purebred](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/purebred/32/46796_2.png) [@Purebred](https://community.cartalk.com/u/Purebred)\ **Post date:** [October 30, 2017, 2:28pm UTC](https://community.cartalk.com/t/ac-and-heat/109000/8 "2017-10-30T14:28:47Z")
I do it frequently, with A/C on max setting adjust heat setting to control humidity levels. As stated above defrost setting runs A/C for same reason. ---
**Author:** ![Whitey](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/whitey/32/24680_2.png) [@Whitey](https://community.cartalk.com/u/Whitey)\ **Post date:** [October 30, 2017, 3:42pm UTC](https://community.cartalk.com/t/ac-and-heat/109000/9 "2017-10-30T15:42:12Z")
My fiancee does that year round. Her car doesn’t have the “set it and forget it” climate controls, so she usually heats up her conditioned air a little so she doesn’t freeze. It hasn’t hurt her compressor. ---
**Author:** ![shadowfax](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/shadowfax/32/13026_2.png) [@shadowfax](https://community.cartalk.com/u/shadowfax)\ **Post date:** [October 30, 2017, 4:25pm UTC](https://community.cartalk.com/t/ac-and-heat/109000/10 "2017-10-30T16:25:42Z")
> [@db4690](#): > > Is there a particular reason for your question? There’s an old myth I hear from time to time about running AC/heat at the same time, or running heat out of the top vents, will damage the system. My mother is one of the believers. No matter what I say, I can’t convince her that it doesn’t hurt anything. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [October 30, 2017, 4:37pm UTC](https://community.cartalk.com/t/ac-and-heat/109000/11 "2017-10-30T16:37:09Z")
> [@shadowfax](#): > > My mother is one of the believers. No matter what I say, I can’t convince her that it doesn’t hurt anything. On the other hand, NOT doing it won’t hurt anything either! Mom’s car, mom’s rules! Let her adjust the controls the way she wants to. ---
**Author:** ![shadowfax](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/shadowfax/32/13026_2.png) [@shadowfax](https://community.cartalk.com/u/shadowfax)\ **Post date:** [October 30, 2017, 5:14pm UTC](https://community.cartalk.com/t/ac-and-heat/109000/12 "2017-10-30T17:14:48Z")
Tell that to my hands when it’s -40 out and I’ve been scraping the windows for what seems like an hour. And she bugs me about it in my car. 😉