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How The Dual-Zone Climate Control Works


c_hunter

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Just read through everything...a big thank you to the OP for clearing up some questions.

 

I do, however, have a question that I don't think has been answered yet. Yesterday, was driving down the highway, and it was about 90 degrees out. Pretty toasty inside the car...very sunny day, windows had been up, so I turned on the AUTO A/C and had both sides set at 65. The cold air was definitely cranking, but I noticed something odd. I had it on full face vent (not sure what the EXACT name is, but it's the setting that just blows air out of the dash vents) because the cool air felt really nice on my sunburned arms. Well, after about 15 minutes of driving on the highway (car was fully warmed up, I was doing about 70ish), I started to realize that the cold air was kind of getting less cold, and it was fairly cyclical. It would be frigid goodness, then, for a few seconds, would just be "normal" not so frigid goodness. Still "cool", but not Ice cold.

 

So, I started timing it. Basically, for 15 seconds, the air would be frigid. For three seconds, it was "cool" (not frigid). 15 seconds, freeze, 3 seconds, normal. And on and on.

 

I realize that the compressor kicks on and off, but I want frigid cold ALL the time when the A/C is on full cold.

 

Has anyone else noticed this???

 

And just for the record, I've only tried it in two vent modes...the face vent, and the combo face/foot vent. Both on 65 with A/C Auto on. AND, the same thing happens at all fan speeds, from low to high.

 

help?

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Just read through everything...a big thank you to the OP for clearing up some questions.

 

I do, however, have a question that I don't think has been answered yet. Yesterday, was driving down the highway, and it was about 90 degrees out. Pretty toasty inside the car...very sunny day, windows had been up, so I turned on the AUTO A/C and had both sides set at 65. The cold air was definitely cranking, but I noticed something odd. I had it on full face vent (not sure what the EXACT name is, but it's the setting that just blows air out of the dash vents) because the cool air felt really nice on my sunburned arms. Well, after about 15 minutes of driving on the highway (car was fully warmed up, I was doing about 70ish), I started to realize that the cold air was kind of getting less cold, and it was fairly cyclical. It would be frigid goodness, then, for a few seconds, would just be "normal" not so frigid goodness. Still "cool", but not Ice cold.

 

So, I started timing it. Basically, for 15 seconds, the air would be frigid. For three seconds, it was "cool" (not frigid). 15 seconds, freeze, 3 seconds, normal. And on and on.

 

I realize that the compressor kicks on and off, but I want frigid cold ALL the time when the A/C is on full cold.

 

Has anyone else noticed this???

 

And just for the record, I've only tried it in two vent modes...the face vent, and the combo face/foot vent. Both on 65 with A/C Auto on. AND, the same thing happens at all fan speeds, from low to high.

 

help?

 

This is "normal".

 

Note that you don't have to be in the auto mode for this to happen. I use my system in manual mode 99% of the time.

 

The air temp does fluctuate. I seems to be worse when steering.

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I have this issue. It's annoying to say the least when you're in snowy mountains and you just want hot air asap...:mad::spin::soap_box::mad:

 

My car is at the dealer for a new valve cover gasket, I have asked them to flush the cooling system too. I'll report back to let you know if it worked.

 

 

Ok, the cooling system flush didn't solve the problem, however when I took it back for a heater core flush it restored the heat on the passenger side.

 

So, because the heater core and the rest of the cooling system are seperated (to prevent a plugged heater core from impeeding the rest of the cooling system) you need to have just the core flushed and backflushed.

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any reasoning on WHY that is? I've never noticed that in another car I've driven. Maybe I just didn't realize that it was happening, but now that I notice it....it bugs the crap out of me :(
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any reasoning on WHY that is? I've never noticed that in another car I've driven. Maybe I just didn't realize that it was happening, but now that I notice it....it bugs the crap out of me :(

 

I really don't know. There's nothing in the design of the air mix system in the cabin that should cause it.

 

 

The air conditioner is also rated at 18,000 BTU/hr, the car should feel like a deep freezer. Instead there are times where getting out to feel a cool ocean breeze seems to bring more comfort.

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  • 3 months later...
I have this issue. It's annoying to say the least when you're in snowy mountains and you just want hot air asap...:mad::spin::soap_box::mad:

 

I have this problem too but the hot air never comes on the passenger side. too bad for them lol.

 

My real problem is the entire A/C system seems to get stuck sometimes where i can have the fan/blower on max and barely any air comes out. but the very next day or for the next week it could work perfectly fine with no problems?

 

Do the flappers get stuck? Do they work on a vacuum? DO they need to be cleaned?

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I have this problem too but the hot air never comes on the passenger side. too bad for them lol.

 

My real problem is the entire A/C system seems to get stuck sometimes where i can have the fan/blower on max and barely any air comes out. but the very next day or for the next week it could work perfectly fine with no problems?

 

Do the flappers get stuck? Do they work on a vacuum? DO they need to be cleaned?

 

No air at all is blowing from the vents or just not warm/cold enough? I was thinking the blower wheel could be plugged, but you said it works OK the day after, so that's not it.

 

When you press the fan speed buttons, can you hear the blower changing speeds? Do you have the airflow problem only when at a certain mode such as through the front dash vents, defroster vent, recirc/fresh, etc...?

 

 

As for your issue with the hot air on the passenger side - I've been through this. Most likely if there is air flow but no hot air, the passenger side of the heater core has become plugged, probably with Subaru Coolant Conditioner used to preserve the head gaskets.

 

This has been a problem on single and dual-zone HVAC systems.

 

In the single zone system, the air box where the air is either heated or cooled is actually separated in the middle. Air for the driver and air for the passenger is drawn over separate parts of the heater core. So it stands to reason that if the passenger side of the heater core is somehow plugged then air on that side will not be heated.

 

I would request that the dealer flush and backflush the heater core. Not a standard "cooling system flush" but flush just the heater core.

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No air at all is blowing from the vents or just not warm/cold enough? I was thinking the blower wheel could be plugged, but you said it works OK the day after, so that's not it.

 

When you press the fan speed buttons, can you hear the blower changing speeds? Do you have the airflow problem only when at a certain mode such as through the front dash vents, defroster vent, recirc/fresh, etc...?

 

 

As for your issue with the hot air on the passenger side - I've been through this. Most likely if there is air flow but no hot air, the passenger side of the heater core has become plugged, probably with Subaru Coolant Conditioner used to preserve the head gaskets.

 

This has been a problem on single and dual-zone HVAC systems.

 

In the single zone system, the air box where the air is either heated or cooled is actually separated in the middle. Air for the driver and air for the passenger is drawn over separate parts of the heater core. So it stands to reason that if the passenger side of the heater core is somehow plugged then air on that side will not be heated.

 

I would request that the dealer flush and backflush the heater core. Not a standard "cooling system flush" but flush just the heater core.

 

There is several problems I have been having.

 

The first thing to start happening is my dual climate control the passenger side does not blow hot really at all. The blower is the same on the passenger as the driver.

 

The new problem is it sounds liek the blower is working and changing speeds but no air is coming out the main vents. I can have it to max and you hear the blower going but you can barely feel a dribble of air coming out.

 

The motor was recently rebuilt and has all new heater core lines as well as everything else. So thats why I was thinking it was a vacuum flapper isue. Not sure though.

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I don't recall if yours has the pocket in behind the glove box that can be removed.. I think it does. You can pull that out and look in behind the side of the air handler box and see if the passenger side air-mix actuator moves when you adjust the passenger side air temp. I'll take a photo of mine later so you know what I'm talking about.

 

 

If it moves then it's likely a heater core issue - was the core itself replaced or just the lines to it?

 

 

As for the low air flow - that's a new one to me. Is it just the main vents that are affected? Does it change when you hit the fresh/recirc button?

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I don't recall if yours has the pocket in behind the glove box that can be removed.. I think it does. You can pull that out and look in behind the side of the air handler box and see if the passenger side air-mix actuator moves when you adjust the passenger side air temp. I'll take a photo of mine later so you know what I'm talking about.

 

 

If it moves then it's likely a heater core issue - was the core itself replaced or just the lines to it?

 

 

As for the low air flow - that's a new one to me. Is it just the main vents that are affected? Does it change when you hit the fresh/recirc button?

 

 

I do have the pocket you are talking about in my glove box but I don't knwo what I am looking at in there.

 

The low airflow is speratic thats why it is weird to me too. This morning it didn't work but coming home from work it did.

 

I tried adjusting all setting but nothing does it. Still no airflow but blower is going and being adjusted.

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  • 1 month later...
  • 2 months later...

I don't believe that there is any "dryer" in an air conditioning system.

 

The evaporator is down under the dash behind the radio. That's where the air is cooled, and in the process moisture in the air condenses on the coils and drips down below the car.

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So, I need to change the compressor, what other hardware would have to be changed? Or are they trying to push the drier or evaporator on me?

 

Someone more experienced in AC should chime in here, but I can't think of why they'd want to change the evaporator unless it has a leak in it.

 

To change the evaporator the entire dash needs to come out. It's a lot of work and there's a good chance something won't get put back together properly.

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All car A/C systems will have either a receiver/dryer or an accumulator. It removes moisture from the refrigerant line. First link I found via Google (not Subaru-specific). A general rule is that any time you open the system, you need to replace this.
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  • 1 month later...
Had the dealer empty the gas today, came home and replaced the compressor. Turned vehicle to make sure all was ok and check if the compressor electromagnet engaged which it didn't. Is there a pressure switch which causes the compressor not to engage if pressure to low?
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  • 1 month later...
My only issue with our system that I believe is a disadvantage is the fact there is no auto passenger mode, like nissan has. Where the passenger side mimics that of the driver. Instead you have to set each individually. That's my only complaint with our dzcc. Edited by 1454
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