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Old 03-02-2015, 01:52 AM   #1
RickV
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Default HVAC Question regarding A/C turning on while on defrost

Does anybody know if the A/C compressor turns on when in defrost in a 1997 Legacy Outback?
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Last edited by RickV; 03-02-2015 at 01:58 AM.
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Old 03-02-2015, 02:37 AM   #2
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usually
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Old 03-02-2015, 02:54 AM   #3
RickV
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I wasn't sure when auto manufacturers started to design this feature into the defrost. I was rather irritated that when I bought my Outback in 2001 that I couldn't run my defrost with the fresh air option - it will only run in recycle mode regardless of the fresh air/recycle button position. It doesn't give the operator the option which I found rather obnoxious. My Toyotas all gave me the option and now I have no control of it. Now recently I learned that I have no control of whether my ECU turns on my A/C compressor in defrost mode. Very irritating as the A/C compressor effects engine performance and gas mileage as well.
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Old 03-02-2015, 02:57 AM   #4
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sell it

or figure out a hack

my 02 wrx had a hack to disable the ac with the defrost/defog

but it works much better with the ac on, really...as It dehumidifies the air
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Old 03-02-2015, 03:36 AM   #5
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I will do some research, thanks for the info Scotty!!! Selling is not an option. I have had this car since 2001. I have many more miles left on this thing and it's been paid off for 11 years.
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Old 03-02-2015, 04:05 AM   #6
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I had the same issue on my 06 impreza. i hated the A/C on defrost. I got into the heater controls and there is a switch the dial turns on when in defrost, i simply unscrewed it and turned it upside down so the peg on the defrost knob couldnt engage it and screwed it back in upside down.... problem solved no more A/C on defrost. If i want the A/C de-humidification i hit the A/C button

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Old 03-02-2015, 04:19 AM   #7
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Wow, great hack!!! Thanks for that info. I will have to take the console apart and see what the switches look like in my Legacy Outback Wagon. It's a 97 and might be a simple fix just like yours. I also want to figure out how to keep the defrost from automatically switching to fresh air even when the recirc button is on. It may just be a similar fix and I will have to check that all out once I have the console taken apart. It won't be any time soon though as I am in Michigan and it's freezing @$$ cold outside and my attached garage isn't heated...
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Old 03-02-2015, 07:52 AM   #8
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It helps to defrost the windows faster, it's actually a smart option to have and not complain about.
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Old 03-02-2015, 08:24 AM   #9
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I'm confused. You have had the car for 14 years and are just now complaining?
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Old 03-02-2015, 08:33 AM   #10
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Activating the AC dehumidifies the air which makes the windows defog faster. Why on earth would you want to disable it...?
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Old 03-02-2015, 11:59 AM   #11
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Quote:
Originally Posted by HinshawWRX View Post
It helps to defrost the windows faster, it's actually a smart option to have and not complain about.
Quote:
Originally Posted by iainb View Post
Activating the AC dehumidifies the air which makes the windows defog faster. Why on earth would you want to disable it...?
Heating the windshield (as opposed to cooling/dehumidifying the air) also works (and doesn't freeze you out when it's cold in the morning). The downside is you have to wait for the coolant to warm up.
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Old 03-02-2015, 12:34 PM   #12
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Quote:
Originally Posted by nsutherl View Post
Heating the windshield (as opposed to cooling/dehumidifying the air) also works (and doesn't freeze you out when it's cold in the morning). The downside is you have to wait for the coolant to warm up.
The air is still hot if you have AC activated with the heat on...
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Old 03-02-2015, 12:57 PM   #13
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Quote:
Originally Posted by nsutherl View Post
Heating the windshield (as opposed to cooling/dehumidifying the air) also works (and doesn't freeze you out when it's cold in the morning). The downside is you have to wait for the coolant to warm up.
You realize you can run the A/C and select the hottest of heat and it will still put out heat right?

The whole point of the defrost system running the A/C is to run the air charge through the dehydrator so there is no moisture in it.

That means no waiting for the coolant to warm up just to run heat and gives faster defogging results.
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Old 03-02-2015, 01:01 PM   #14
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^ what he said, Just think about it like running a heat pump in your home! It works both ways Heating and Cooling
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Old 03-02-2015, 01:03 PM   #15
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obviously he does not understand that AC can be and is used with hot air (to dehumidify it), the reason it is set up to automatically turn on when defrost is selected.

Dopeslap, systems automated to bypass the failure of understanding between seat and steering wheel.
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Old 03-02-2015, 01:04 PM   #16
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Quote:
Originally Posted by iainb View Post
The air is still hot if you have AC activated with the heat on...
Quote:
Originally Posted by HinshawWRX View Post
You realize you can run the A/C and select the hottest of heat and it will still put out heat right?

The whole point of the defrost system running the A/C is to run the air charge through the dehydrator so there is no moisture in it.

That means no waiting for the coolant to warm up just to run heat and gives faster defogging results.
Yes, thanks.

I believe that the OP's wish was to defrost without the A/C on. Just pointing out that it is still possible to defog/defrost without the compressor on.

Additionally, what is a dehydrator...? Are you thinking of dehumidifier?
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Old 03-02-2015, 01:05 PM   #17
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And keep in mind the compressor won't actually kick on anyway if the outside air is much below 32 degrees, no matter what your dash controls tell it to do.
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Old 03-02-2015, 01:09 PM   #18
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Quote:
Originally Posted by nsutherl View Post
Yes, thanks.

I believe that the OP's wish was to defrost without the A/C on. Just pointing out that it is still possible to defog/defrost without the compressor on.

Additionally, what is a dehydrator...? Are you thinking of dehumidifier?
Dehydrator:

noun

1. a person or thing that dehydrates.

2. a device, apparatus, or appliance that dehydrates food for preservation.
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Old 03-02-2015, 01:16 PM   #19
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Originally Posted by HinshawWRX View Post
Dehydrator:

noun

1. a person or thing that dehydrates.

2. a device, apparatus, or appliance that dehydrates food for preservation.
Thanks for that... Was more curious about the "dehydrator" in a car's A/C system.

Usually, the "dehydrator" in an A/C system is just the cooling coil, although nobody calls it that. There's not like, a bank of "dehydrators" the air gets diverted to...
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Old 03-02-2015, 01:25 PM   #20
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Originally Posted by rex864 View Post
^ what he said, Just think about it like running a heat pump in your home! It works both ways Heating and Cooling
Not at all like a heat pump in your home. A heat pump uses the compressor to either cool the air (normal cycle direction) or heat the air (cycles reverses direction, therefore rejecting compressor heat to the space).

When your car is in defrost mode, the compressor/AC cools and dehumidifies the air, then re-heats it using the heater core from the coolant loop.

Last edited by nsutherl; 03-02-2015 at 01:30 PM. Reason: clarity
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Old 03-02-2015, 03:47 PM   #21
iainb
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Quote:
Originally Posted by nsutherl View Post
Yes, thanks.

I believe that the OP's wish was to defrost without the A/C on. Just pointing out that it is still possible to defog/defrost without the compressor on.
Of course it is possible, it just isn't as effective and takes longer.

Which is the point the rest of us are trying to make.

Who modifies their car so it works worse than before?
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Old 03-02-2015, 04:30 PM   #22
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Quote:
Originally Posted by iainb View Post
Of course it is possible, it just isn't as effective and takes longer.

Which is the point the rest of us are trying to make.
Agreed. His question was can I defrost with the A/C off. Answer: yes, but there's a reason the A/C comes on (it works better).

Quote:
Originally Posted by iainb View Post
Who modifies their car so it works worse than before?
LOL. I believe this is story of NASIOC's life. You can't save an idiot from him/herself.
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Old 03-02-2015, 09:49 PM   #23
notnu2subru
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Well, that seems just a bit harsh. It's a suabaru-owner thing, we like certain things, certain ways, just check the tire threads, the oil threads, the exhaust threads, in fact any thread. That's why we buy these cars, a bit off the beaten path, that's where we like to go. I personally like the exact response in how to hack the "problem" AND w/pics....NASIOC!
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Old Yesterday, 04:39 AM   #24
RickV
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OK guys, I never thought this post was going to turn into this many comments but my reason for not wanting the A/C to turn on during defrost is mainly during the freezing @$$ cold winters here in Michigan. The defrost setting definitely is noticeably colder than the dash/floor heater setting set to recirc in the winter when it's 10 degrees outside and the car isn't completely warmed up yet. When there is moisture in the internal air at that temp it turns to ice on the windows inside the car. Yes, in the warmer weather the A/C defrost combo works great. The inability to run the defrost in the recirc mode is rather irritating as well especially in the warmer weather and the external humidity is higher than the internal humidity and I don't want to run the A/C. So that is my reasoning for the original post.
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Old Yesterday, 04:56 AM   #25
RickV
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As for Mike.J's comment about having the car for 14 years -YES, I am just now researching options because until recently I never knew that it was typical for the defrost to engage the A/C. Also, I attributed the cooler defrost during freezing sub sero weather to the fact that the defrost forced the system to fresh air mode even when the recirc was turned on.
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