AC question
07-07-2004, 07:07 AM
#1
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Posts: 87
AC question
My AC is blowing pretty cold air, so I'm overall satisfied with it. However, I don't notice that big of a difference with the temp set at 75 vs. 60. I've tried after driving for awhile to make sure it's had enough time to sufficiently kick in, but the coldness doesn't seem to be that big of a difference. I'm curious to see if everyone else sees a drastic difference between 60 and 75, or if the difference is not that noticible when sticking your hand in front of it.
07-07-2004, 08:02 AM
#3
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Join Date: May 2004
Posts: 29
Somewhere in our car there is a thermostat that controls the AC. You don't feel a difference because the compressor blows air out at a certain rate, not a certain temperature. Raising or lowering the temp. setting only increases or decreases the amount of air blown into the cabin of the car. For this reason, the air feels the same at either temp. Once the thermostat begins to reach the desired temperature, the rate of airflow slows down. Hope this helps. 
07-07-2004, 09:42 AM
#4
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Join Date: Jun 2003
Posts: 249
Thats right only it is not the compressor that controls the flow, it is the blower motor. (The compressor does something completely different)
I've noticed it too. The thing is though, the air coming out of the dash at 70 is not coming out of the dash at 70 degrees. The car is trying to regulate the internal temperture, not the duct temperture. So what is happening it, the air coming out of the dash is say 45 degrees, it comes out at an equal rate of the cars heat index. (the opposite rate the car heats up at from sunlight) So if you lower the temperture on the screen, you are just making the car push out more air into the cabin too cool it even more.
I've noticed it too. The thing is though, the air coming out of the dash at 70 is not coming out of the dash at 70 degrees. The car is trying to regulate the internal temperture, not the duct temperture. So what is happening it, the air coming out of the dash is say 45 degrees, it comes out at an equal rate of the cars heat index. (the opposite rate the car heats up at from sunlight) So if you lower the temperture on the screen, you are just making the car push out more air into the cabin too cool it even more.
07-07-2004, 10:36 AM
#5
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Location: a meadow south of Atlanta
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Several here are on top of this. The temp of the air coming from the ducts should be constant.
If the temp in the car is well above the selected temp, the system will select the highest speed for the blower fan. Whether the difference is ten degrees or twenty degrees won't matter, as either will use the top blower speed.
Once the temp in the car is at or near the selected temp, the volume of air decreases. Once the selected temp is reached, only enough air to keep the temp at that level will be coming from the vents.
I don't know the actual temp of the air coming from the ducts of the '04 Maxima, but when I have measured it in other vehicles over the years, systems that were operating well usually had duct temps around 55 to 57 degrees. That would be after the system has been running for several minutes. This temp could, of course, be slightly affected by unusually hot weather, moreso if the car is stuck in traffic and air is not passing thru the AC radiator.
Fifty-six degrees may not sound very cold, but it is more than cool enough to keep a car comfortable. Systems putting out air colder than that would be more prone to the infamous 'freeze-ups' that were the bane of auto AC during the 1950s thru 1975 or so.
The placement of the vents and shape of the cabin of the '04 Maxima make it difficult to keep some of the duct air from hitting the driver and front passenger. Having air colder than 56 degrees would exacerbate that situation.
My only wish is that there were additional ducts for the rear seats. The wimpy two at the rear of the front console are inadequate. Having more ducts in the rear would also help when no passengers are using the rear seat in that the car could be cooled more quickly without blowing the toupes off the front seat occupants.
But then my application for employment by the Nissan design group in California was rejected, so . . .
If the temp in the car is well above the selected temp, the system will select the highest speed for the blower fan. Whether the difference is ten degrees or twenty degrees won't matter, as either will use the top blower speed.
Once the temp in the car is at or near the selected temp, the volume of air decreases. Once the selected temp is reached, only enough air to keep the temp at that level will be coming from the vents.
I don't know the actual temp of the air coming from the ducts of the '04 Maxima, but when I have measured it in other vehicles over the years, systems that were operating well usually had duct temps around 55 to 57 degrees. That would be after the system has been running for several minutes. This temp could, of course, be slightly affected by unusually hot weather, moreso if the car is stuck in traffic and air is not passing thru the AC radiator.
Fifty-six degrees may not sound very cold, but it is more than cool enough to keep a car comfortable. Systems putting out air colder than that would be more prone to the infamous 'freeze-ups' that were the bane of auto AC during the 1950s thru 1975 or so.
The placement of the vents and shape of the cabin of the '04 Maxima make it difficult to keep some of the duct air from hitting the driver and front passenger. Having air colder than 56 degrees would exacerbate that situation.
My only wish is that there were additional ducts for the rear seats. The wimpy two at the rear of the front console are inadequate. Having more ducts in the rear would also help when no passengers are using the rear seat in that the car could be cooled more quickly without blowing the toupes off the front seat occupants.
But then my application for employment by the Nissan design group in California was rejected, so . . .
07-07-2004, 10:38 AM
#6
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Join Date: Jul 2003
Posts: 92
yes, however... adjusting the temp control up or down does make a difference in the temperature of the air blowing from the vents. I think what scavynger and I were getting at is that, regardless of blower speed, the temp does adjust to warmer from around the 70 deg. setting and on up. Below 70 there is not temp. difference, down to 60.
All I'm saying is that it seems having the setting below 70 is pointless, as it doesn't do anything and most people don't want their cabin temp. below that mark. The air temp. quits changing below 70.
Know what I mean? Oh fugit anyways... guess it doesn't really matter.
All I'm saying is that it seems having the setting below 70 is pointless, as it doesn't do anything and most people don't want their cabin temp. below that mark. The air temp. quits changing below 70.
Know what I mean? Oh fugit anyways... guess it doesn't really matter.
07-07-2004, 11:05 AM
#7
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Location: a meadow south of Atlanta
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If the setting is at a temp above the cabin temp, naturally the air from the ducts will not be all air cooled by the compressor; the system will mix cooled air with non-cooled air.
Assuming the normal situation where air in the cabin is warmer than the driver-selected temp, the temp of the air coming from the vents does not change as the setting is moved downward. But the blower speed does. At least on my SL.
If I have the temp set on 70, once the temp nears 70 in the cabin, the blower slows considerably. If I move the setting down to 69, the blower speeds up slightly. However, if I move the setting down to 65, the blower immediately speeds way up, and remains there until the cabin temp reaches 65.
In hot weather, it will be difficult to get the cabin temp all the way down to 65, hence the blower speed will probably stay the same, whether the setting is 60, 62, 64 or even 66.
Assuming the normal situation where air in the cabin is warmer than the driver-selected temp, the temp of the air coming from the vents does not change as the setting is moved downward. But the blower speed does. At least on my SL.
If I have the temp set on 70, once the temp nears 70 in the cabin, the blower slows considerably. If I move the setting down to 69, the blower speeds up slightly. However, if I move the setting down to 65, the blower immediately speeds way up, and remains there until the cabin temp reaches 65.
In hot weather, it will be difficult to get the cabin temp all the way down to 65, hence the blower speed will probably stay the same, whether the setting is 60, 62, 64 or even 66.
07-07-2004, 11:09 AM
#8
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Join Date: Oct 2003
Posts: 107
Originally Posted by Spunko
yes, however... adjusting the temp control up or down does make a difference in the temperature of the air blowing from the vents. I think what scavynger and I were getting at is that, regardless of blower speed, the temp does adjust to warmer from around the 70 deg. setting and on up. Below 70 there is not temp. difference, down to 60.
All I'm saying is that it seems having the setting below 70 is pointless, as it doesn't do anything and most people don't want their cabin temp. below that mark. The air temp. quits changing below 70.
Know what I mean? Oh fugit anyways... guess it doesn't really matter.
All I'm saying is that it seems having the setting below 70 is pointless, as it doesn't do anything and most people don't want their cabin temp. below that mark. The air temp. quits changing below 70.
Know what I mean? Oh fugit anyways... guess it doesn't really matter.
You're right, Spunko....the temperature definitely does change along with the fan speed as adjustments are made.
07-07-2004, 11:56 AM
#9
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Join Date: Jun 2004
Location: Sarasota, FL
Posts: 207
Sounds like sound answers....if there is anything superficial I could change about my car, this is it.
I live in FL and there isn't a day of the year (except on those that rain all day and maybe 2-3 weeks of cold weather) that I can get into my car and not want to cool it off.
And you all know when that fan is on low, and you adjust it and it kicks all the way into high it sounds like a plane taking off. That is the noisiest AC system and sometimes I have to turn it down when on the cell so I can hear :P
I'm not sure if it's the shape of the vents, or because maybe there are fewer of them than in some other cars or what, but it definitely gets loud when on high.
I live in FL and there isn't a day of the year (except on those that rain all day and maybe 2-3 weeks of cold weather) that I can get into my car and not want to cool it off.
And you all know when that fan is on low, and you adjust it and it kicks all the way into high it sounds like a plane taking off. That is the noisiest AC system and sometimes I have to turn it down when on the cell so I can hear :P
I'm not sure if it's the shape of the vents, or because maybe there are fewer of them than in some other cars or what, but it definitely gets loud when on high.
07-07-2004, 12:09 PM
#10
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Join Date: May 2004
Posts: 87
There's an option for the AC called Auto. When it's turned on, I see the same behavior you are mentioning. Where it will adjust the fan speed according to the temperature you set. However, when it's turned off, the fan speed is controlled manually. Is the blower speed you are talking aboud different than the fan speed?
If not, it seems like the temperature setting is pointless when using the AC in the manual mode where the driver determines the fan speed.
If not, it seems like the temperature setting is pointless when using the AC in the manual mode where the driver determines the fan speed.
07-08-2004, 11:54 AM
#11
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Join Date: May 2004
Posts: 2
So if I understand this thread correctly, are you saying that regardless of the temperature that you set, the air that comes out will have the same coldness? Wouldn't this defeat the purpose of the dual climate controls? If the driver is set at 65 and teh passenger at 70, what would be the difference if the coldness comes out the same? The vents arn't capable of blowing at different fan speeds.
07-08-2004, 03:57 PM
#12
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Location: a meadow south of Atlanta
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laurenceau - After having experimented with this dual system, I feel the biggest differential between 'sides' will be noticed in cold weather.
I haven't been able to satisfy myself the system has the ability to mix less-cold air with the air conditioned air to reduce the output temp on one side. I suspect it may not. My wife and I find our best control in hot weather is via partially closing vents for the side wanting less air.
In cold weather, the system seems to be able to better control the degree of warmth between sides.
I realize I could be overlooking some things, but this is what I have observed.
I haven't been able to satisfy myself the system has the ability to mix less-cold air with the air conditioned air to reduce the output temp on one side. I suspect it may not. My wife and I find our best control in hot weather is via partially closing vents for the side wanting less air.
In cold weather, the system seems to be able to better control the degree of warmth between sides.
I realize I could be overlooking some things, but this is what I have observed.
07-08-2004, 08:11 PM
#13
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Posts: 87
yeah...i've noticed that too...early in teh morning before it get's scorching hot, you can feel 60 a little cooler than 75, but during the afternoon, there isn't much difference. It's still cold, no big complaints, I was just wondering if everyone had noticed the same thing, or if I was the minority and everyone else has a frigid noticibly cold 60 degree.
07-09-2004, 08:17 AM
#14
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Join Date: Oct 2003
Posts: 880
Part of the difference you're feeling in the temperature is the fact that "recirculate" kicks in when the temperature is set to a low setting relative to the cabin temperature.
For example, if you get into a car sitting in the sun, and the inside temperature is 90 degrees, and you set your A/C to 60, the system will choose recirculate to speed up the cooldown of the cabin. Then, when the cabin temp starts to come down, it will switch back to "outside air" to bring fresh air in. When on recirculate, the air coming out of the vents will be colder, because the system is having to cool cooler air to begin with and therefore can operate more efficiently. (At least that's what happens when the system is set to "Auto").
On this same general topic, I'll say this: I like the fact this system puts out a lot of air. Too many A/C systems these days try to be too "non-intrusive", so they keep fan speeds very low and almost unnoticeable. Hell's bells, I live in Texas, and when I want a car cooled down I want it cooled right now. Don't pussyfoot around with little whispers of air ... blow my hat off!
Mike
For example, if you get into a car sitting in the sun, and the inside temperature is 90 degrees, and you set your A/C to 60, the system will choose recirculate to speed up the cooldown of the cabin. Then, when the cabin temp starts to come down, it will switch back to "outside air" to bring fresh air in. When on recirculate, the air coming out of the vents will be colder, because the system is having to cool cooler air to begin with and therefore can operate more efficiently. (At least that's what happens when the system is set to "Auto").
On this same general topic, I'll say this: I like the fact this system puts out a lot of air. Too many A/C systems these days try to be too "non-intrusive", so they keep fan speeds very low and almost unnoticeable. Hell's bells, I live in Texas, and when I want a car cooled down I want it cooled right now. Don't pussyfoot around with little whispers of air ... blow my hat off!
Mike
07-09-2004, 05:46 PM
#15
Great post, helped a lot with some of my HVAC concerns but:
when it inevitably/unfortunetly gets colder out, should the A/C be used to heat the car? I know that the defrost is useless w/o the A/C. The windshield fogs with just heat on, but clears instantly with A/C. But in the winter, shouldn't it just use the heat from the engine? Seems a waste of gas to use the A/C in the winter too.
The one night going to work, w/ a temp drop from the rain, I had to defrost with the A/C. But when I got off work in the morning the interior windshield was covered with condensation.
when it inevitably/unfortunetly gets colder out, should the A/C be used to heat the car? I know that the defrost is useless w/o the A/C. The windshield fogs with just heat on, but clears instantly with A/C. But in the winter, shouldn't it just use the heat from the engine? Seems a waste of gas to use the A/C in the winter too.
The one night going to work, w/ a temp drop from the rain, I had to defrost with the A/C. But when I got off work in the morning the interior windshield was covered with condensation.
07-09-2004, 06:15 PM
#16
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Well, now that Maxima80 has brought up the use of the AC during cool weather dehumidification, I might as well throw in an excerpt from the Owner's Manual that sort of stuck in my mind:
'When the front defroster button is pushed, the air conditioner will automatically be turned on at outside temperatures above 23 degrees F (-5 degrees C). THE AIR CONDITIONING SYSTEM WILL CONTINUE TO OPERATE UNTIL THE FAN CONTROL DIAL IS TURNED TO OFF, OR THE VEHICLE IS SHUT OFF, even if the air control button is used to select a position other than the defrost position. This dehumidifies the air, which helps degog the windshield. The air recirculate mode automatically turns off, allowing outside air to be drawn into the pasenger compartment to further improve the defogging performance.'
This is on page 4-17 of the owner's Manual. The Caps are mine (for emphasis).
Based on that, I feel it would be possible to press the defrost button early one morning at the start of a long trip, and unless a stop was made along the way, or the fan control was turned to 'off' (unlikely in winter weather), the AC would operate all day, even though the purpose it was used for may have ceased to exist soon after the trip started.
I have mixed feelings about this.
'When the front defroster button is pushed, the air conditioner will automatically be turned on at outside temperatures above 23 degrees F (-5 degrees C). THE AIR CONDITIONING SYSTEM WILL CONTINUE TO OPERATE UNTIL THE FAN CONTROL DIAL IS TURNED TO OFF, OR THE VEHICLE IS SHUT OFF, even if the air control button is used to select a position other than the defrost position. This dehumidifies the air, which helps degog the windshield. The air recirculate mode automatically turns off, allowing outside air to be drawn into the pasenger compartment to further improve the defogging performance.'
This is on page 4-17 of the owner's Manual. The Caps are mine (for emphasis).
Based on that, I feel it would be possible to press the defrost button early one morning at the start of a long trip, and unless a stop was made along the way, or the fan control was turned to 'off' (unlikely in winter weather), the AC would operate all day, even though the purpose it was used for may have ceased to exist soon after the trip started.
I have mixed feelings about this.
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