# Defroster runs AC **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** legacy, subaru\ **Created:** [January 22, 2017, 6:01pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909 "2017-01-22T18:01:43Z")\ **Posts on this page:** 20\ **Page:** 3
**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:** [January 23, 2017, 10:54pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/41 "2017-01-23T22:54:13Z")
> [@asemaster](#): > > When DEF is selected, the AC compressor runs, regardless of whether you have AC selected or not. Don’t believe me? Go turn on your DEF and see if the AC compressor cycles on and off. Yes, when I turn on the defroster, my A/C light automatically comes on, but if I press the A/C button, it turns off the air conditioner. Back when I had a working compressor, turning off the A/C would cause the compressor to disengage, even if the controls were in defrost mode to direct air at the windshield. I’m not sure why you think I don’t believe you about **your car**. I believe you know **your car** , and perhaps many other cars, better than I know your car, but you don’t know **my car** better than I know my car. I’ve been driving and maintaining my car for 18 years, and I have evidence you’re wrong when you say **all cars** behave the same way, because mine doesn’t. Back when I had working A/C, pressing the A/C button to disengage the A/C would disengage it whether it was running in defrost mode or not. ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [January 23, 2017, 10:58pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/42 "2017-01-23T22:58:46Z")
> [@Nevada\_545](#): > > The Highlander owners manual states that you should switch on the A/C for more effective defogging when using the defroster. The A/C operation is automatic with the defroster on with the ES350 as stated in the owners manual, I went outside and tested one. Maybe that’s the newer model of the ES350…but it certainly is NOT how it operates on my wifes 07 ES350. You have to manually switch the AC on by pressing the AC button. It does NOT turn on automatically. ---
**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:** [January 23, 2017, 11:03pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/43 "2017-01-23T23:03:00Z")
> [@MikeInNH](#): > > it certainly is NOT how it operates on my wifes 07 ES350. You have to manually switch the AC on by pressing the AC button. I wish mine were set up like that. 😌 ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [January 23, 2017, 11:07pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/44 "2017-01-23T23:07:03Z")
My '96 ES turned on automatically: “FRONT WINDSHIELD mode – Directs air flow mostly to the windshield and front side windows. When this mode is selected while operating in automatic mode, the air conditioning is set to operate and the OUTSIDE AIR mode is set.” ---
**Author:** ![keith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/keith/32/5518_2.png) [@keith](https://community.cartalk.com/u/keith)\ **Post date:** [January 23, 2017, 11:23pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/45 "2017-01-23T23:23:37Z")
> [@Whitey](#): > > I think you’re confused because you’re over-analyzing how the refrigerant behaves. When the refrigerant absorbs the heat in the evaporator, it turns from a liquid into a gas (which is why we call it the evaporator). When the refrigerant goes out to the condenser, it is re-compressed into a liquid, which releases the heat energy the refrigerant carried out of the car/house from the evaporator. Isn’t that what I said? ---
**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\ **Post date:** [January 23, 2017, 11:28pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/46 "2017-01-23T23:28:33Z")
If one hates it that much can’t you pull a relay or fuse, or do a winter belt that bypasses the compressor? ---
**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:** [January 24, 2017, 12:26am UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/47 "2017-01-24T00:26:35Z")
You said an air conditioner isn’t a heat pump. Actually it is, which is why I thought the additional explanation might be necessary. …but don’t let that stop you from quoting me out of context if that what it takes to make you feel better. 😉 ---
**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:** [January 24, 2017, 12:39am UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/48 "2017-01-24T00:39:58Z")
Shape your lips like you were whistling. Blow into your hand. Feels cool, doesn’t it? Yet it comes out of your body at 98.6F. Compress matter and it heats up. Expand matter and it absorbs heat (cools). The way an AC system works is basic. Refrigerant is compressed, whereupon it becomes hot. The heat is removed by a small radiator called a condenser. The still-compressed but now cooled refrigerant is then pumped through a small orifice, just like the opening in your lips, past through which it expands rapidly, becoming chilled. The now-chilled refrigerant is then passed through a small radiator (called an evaporator). Warm cabin air is passed through the radiator and the heat from the cabin air is absorbed through the fins by the chilled refrigerant. Heat moves from warmer matter (the cabin air) to cooler matter (the refrigerant). The now-warmed and decompressed refrigerant goes back to the compressor, wherein it’s again compressed and the cycle begins again. Moisture is removed because the warm, moisture-laden cabin air loses its ability to hold the moisture as it’s chilled at the evaporator core fins. It deposits the moisture on the fins as it chills. ---
**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\ **Post date:** [January 24, 2017, 12:44am UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/49 "2017-01-24T00:44:56Z")
My understanding of a heat pump is in winter it captures heat to flow to the interior, in summer captures heat to blow to the outdoors. Now I love a kerosene powered refrigerator, In my concept a heat pump is just a reversal of heating and cooling mechanics for winter and summer. ---
**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:** [January 24, 2017, 12:51am UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/50 "2017-01-24T00:51:59Z")
I’m sure there is some confusion related to “heat pump” being used as a trade term used to refer to a more efficient heating systems for our homes, but I don’t think cars use that kind of technology because they pull heat from the engine. ---
**Author:** ![keith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/keith/32/5518_2.png) [@keith](https://community.cartalk.com/u/keith)\ **Post date:** [January 24, 2017, 12:52am UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/51 "2017-01-24T00:52:04Z")
Yes technically an air conditioner is a heat pump, but in the industry jargon and popular usage, a heat pump works both ways, as a heater and an air conditioner. An air conditioner in a car is not a heat pump in the way most people think of a heat pump. I didn’t quote you out of context either. The quote was complete. ---
**Author:** ![insightful](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/insightful/32/2732_2.png) [@insightful](https://community.cartalk.com/u/insightful)\ **Post date:** [January 24, 2017, 12:57am UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/52 "2017-01-24T00:57:33Z")
> [@Whitey](#): > > I don’t think cars use that kind of technology because they pull heat from the engine. Some model of Prius do. ---
**Author:** ![asemaster](https://avatars.discourse-cdn.com/v4/letter/a/5f9b8f/32.png) [@asemaster](https://community.cartalk.com/u/asemaster)\ **Post date:** [January 24, 2017, 4:04am UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/53 "2017-01-24T04:04:23Z")
> [@MikeInNH](#): > > First off - I don’t have a 14 Pathfinder. I have a 14 Highlander. > > And I can turn the Defrost on without turning on the AC. The light is not on and the AC is not working. Verifiable. When I turn the AC there is a significant difference between the AC being on and when the AC isn’t on. Must have had Pathfinder on the mind, was starting a Pathfinder timing belt job this afternoon. ---
**Author:** ![asemaster](https://avatars.discourse-cdn.com/v4/letter/a/5f9b8f/32.png) [@asemaster](https://community.cartalk.com/u/asemaster)\ **Post date:** [January 24, 2017, 4:12am UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/54 "2017-01-24T04:12:30Z")
Touche. I think every blanket statement has holes in it, much like saying cigarettes cause cancer or rebuilt water pumps are no good. I think that your year Civic is about the last that allowed def operation without AC operation. Hondas and Toyotas are, I believe, the only cars that ever allowed it. ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [January 24, 2017, 1:16pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/55 "2017-01-24T13:16:22Z")
> [@asemaster](#): > > Civic is about the last that allowed def operation without AC operation My wife’s 87 and 96 Accords you could turn defrost on without AC. But the Civic did turn AC On when on defrost. ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/48514_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [January 24, 2017, 1:30pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/56 "2017-01-24T13:30:30Z")
> [@asemaster](#): > > I think that your year Civic is about the last that allowed def operation without AC operation. Hondas and Toyotas are, I believe, the only cars that ever allowed it. IIRC, some Chrysler products (circa 1990s??) allowed you to run the defroster w/o the A/C compressor. After pushing the defroster button “in”, if you then pulled it out, the defroster function would keep working, but the compressor was halted. ---
**Author:** ![sgtrock21](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/sgtrock21/32/246_2.png) [@sgtrock21](https://community.cartalk.com/u/sgtrock21)\ **Post date:** [January 24, 2017, 3:15pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/57 "2017-01-24T15:15:07Z")
The only way to turn on A/C in my 2010 Kia is by pushing the button and turning on the fan to at least position 1. I can turn A/C off and on using the fan switch or the A/C button. ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [January 24, 2017, 3:25pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/58 "2017-01-24T15:25:37Z")
Are you sure? This is from the 2010 Soul owners manual: To defog inside windshield 1. Set the fan speed to the desired position except “0” position. 2. Select desired temperature. 3. Select the or position. 4. The outside (fresh) air and air conditioning will be selected automatically. If the air conditioning and outside (fresh) air position are not selected automatically, press the corresponding button manually. ---
**Author:** ![sgtrock21](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/sgtrock21/32/246_2.png) [@sgtrock21](https://community.cartalk.com/u/sgtrock21)\ **Post date:** [January 24, 2017, 7:35pm UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/59 "2017-01-24T19:35:03Z")
This is from my 2010 Forte owners manual: Manual climate control system (which my Forte is equipped with) To defog inside windshield 1. Select any fan speed except “0” position. 2. Select desired temperature. 3. Select the (symbol for defrost/floor combination) or (symbol for defrost only) position. 4. The outside (fresh) air will be selected automatically. If the outside (fresh) air position is not selected automatically, press the corresponding button manually. A/C is not addressed. If I want to add A/C (which I normally do) I have to push the A/C button to activate it. Even the Automatic climate control system requires pushing the A/C button to activate A/C. ---
**Author:** ![insightful](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/insightful/32/2732_2.png) [@insightful](https://community.cartalk.com/u/insightful)\ **Post date:** [January 25, 2017, 2:41am UTC](https://community.cartalk.com/t/defroster-runs-ac/98909/60 "2017-01-25T02:41:36Z")
My 2010 Insight turns the compressor on with DEFROST but the compressor can be turned off with a push of the A/C button. The 2017 Ford fusion Hybrid has both a defrost button and a MAX defrost button, whatever that means. [Previous page](https://community.cartalk.com/t/defroster-runs-ac/98909.md?page=2) [Next page](https://community.cartalk.com/t/defroster-runs-ac/98909.md?page=4)