A/C and Defrost

[elfwizard]

My Wife has a 2002 Civic LX. Is there a Way to stop the A/C from coming on when you turn on the Defrost? It just sucks Gas down. We Live in WA state in the US. Defrost is basically on ALL THE TIME!!
There has to be a way to disable it from coming on. Dealer says there isn't. I thought you performance guys might know.

Thanks!

[Swonder67]

you can't just hit the AC button again to turn it off when you go to deforst? Thats waht I do, but I have a 6th gen

[LX98Civic]

Originally posted by Swonder67
you can't just hit the AC button again to turn it off when you go to deforst? Thats waht I do, but I have a 6th gen

Same here for my 6th gen.
I just make sure the green light is off :flash:

[90CRXZCSi]

the a/c can go off but in the manual it tells you to turn on the a/c when the defrost is on. I guess it keeps it cool enough to where it doesnt fogg up your windows i guess.

[praxis]

The A/C and defrost work together to keep the condensation down, I beleive.

Once the fog is gone turn the A/C off and back on if it starts to fog back up.

[jimmyfunk]

I don't believe there is a way to turn the AC off during defrost in the 2002 model. The reason it does this is because the AC equalizes the moisture on the inside of the windshield to that on the outside, making it easier to get rid of the "fog" effect.

[Mirt3]

my 92 civic is constantly fogging up even when its not very cold out...its a huge problem because the heater gets so hot that the defroster burns yer eyes when its on...its really annoying, how can i fix it?

[elfwizard]

No. It wont turn off. You can hit the AC and it stays on. I was wondering if anyone has ever looked into it. Is there a Switch that it hits when i Switch it to Defrost that turns the AC on? Is there a Fuse I can Pull? I know what THEY SAY its for, but good old fashioned Defrost works fine, no use to waste GAS when the A/C is on.

[wwest]

Originally Posted by foggingup2003

we have a 2003 nissan quest, when two adults and four children get in the car the interior foggs up and it is difficult to clear up. Van has been to dealer already, they found no problems, used ac with heat, read manual with their suggestion, still didn't help. this problems only happens in the cold weather. any help or suggestions would be greatly appreciated. Anybody incounter this problem also?

Given that your vehicle is of Asian/Japanese origin the climate control system is most likely of NipponDenso, Denso USA, design. With the change-over to the new less efficient non-freon refrigerant several design changes were deemed necessary.

First, the A/C cooling evaporator, heat exchanger, was made a lot more dense and complex. The more chilled surface area for the air to flow over, the higher will be the efficiency of the heat transfer.

The second issue is more directly pertinent to your problem. The slower the air flows over the evaporator's cooling surfaces the more it will be cooled and the more it is cooled raises the likihood that it will be simultaneously DEHUMIDIFIED.

Another benefit of the lowering of the incoming airflow rate is better MPG, something I'm sure the automotive manufaturers haven't over-looked. Almost all modern day passenger vehicles are very well sealed against atmospheric outflow for these reasons.

The way NipponDenso has chosed to keep the evaporator airflow as low as possible is by restricting the cabin atmosphere OUTFLOW. The result of that is that during the cooler months it will be really easy for the passenger cabin to become extremely humid, so humid that the windows and windshield interior surfaces, cooled continously by exposure to COLD outside atmosphere, begin to fog over.

My suggestions...

If it is possible to completely disable the A/C during the winter months then do so. My 01 RX300 has C-best options which allowed the dealer to "unlink" the automatic operation of the A/C in both "normal" and defrost/defog/demist modes. ON a previous 92 LS400 I fooled the system into thinking the OAT was below 32F by adding a resistor in series with the OAT sensor. I have also, on occassion, simply disconnected the A/C compressor clutch electrical circuit. My 01 Porsche has a switch added within the glove box that does that.

If you park the vehicle inside it will help to leave a window or windows open so the cabin can more completely dry out. During A/C operation the ~10,000 square inches (92 LS) of evaporator surface area will become saturated, clogged, with mositure and while much of that will drain away via the provided drain a lot will remain and then evaporate into the A/C plenum and thus into the passenger cabin at the first start of the system blower.

My most common occurance of intermittent and spontaneous windshield fogging was about 5 miles into my morning trip to the office during the cooler months. That instance was cured, mostly, by leaving the windows slightly open during the night in the garage.

Another instance is that the A/C compressor will oftentimes shut down spontaneously, without any indication to you, if the OAT declines to near or below freezing. A few minutes after that happens the condensed moisture remaining on the evaporator will begin to evaporate into the airflow entering the passenger cabin.

Be VERY CAREFULL, this can be a very HAZARDOUS situation.

If you are traveling in a colder climate and begin to see wisps of condensation on the interior surface of the windshield DO NOT ACTIVATE the defrost/demist/defog function before you turn the system heat all the way to MAX!

Those wisps of condensation might be indicative of the A/C compressor having previously shut down due to low OAT and now if you activate the defrost/defog/demist function the COLD windshield will become suddenly opaque from condensation due to the moisture bomb building up with the A/C plenum.

The best procedure to use if you sense that the humidity is to high within the passenger cabin is to lower the rear windows slightly and quickly purge the humid atmosphere from the cabin.

While I remain a strong advocate of the use of A/C to dehumdify the incoming cabin airflow and thereby help to remove windshield condensation and prevent it's formation, I don't understand why, other than the slight discomfort one might feel, the defrost/defog/demist airflow isn't also HEATED.

Wwith Outside Air Temperatures, OAT's, below about 55F it is impossible to predict whether or not the the A/C can be efficient enough to be of any help. The A/C's dehumidifcation efficiency is a function of the relative humdity of the incoming airflow. The lower the temperature of the incoming airflow the lower is the probability of efficient dehumdification by the A/C until at about 35F it is practically non-existent.

[GScivic7]

Originally Posted by jimmyfunk

I don't believe there is a way to turn the AC off during defrost in the 2002 model. The reason it does this is because the AC equalizes the moisture on the inside of the windshield to that on the outside, making it easier to get rid of the "fog" effect.

huh??? All AC does is de-humidify the air. That's why, when you want to get rid of all the moisture on the inside of your windows you turn the heat up, hit the AC and open the vents so it circulates all the humid air inside out and all the air coming in is dehumidified by the AC.

[mycivic]

I have the 2003 model. I think it should be more or less the same with the 2002. Just push the A/C button and you should be fine.

[i_a_n112784]

Just press the A/C button to turn it off. But it needs to run in the winter for a couple of minutes every week (or so) to lubricate the system, since the oil is in the refrigerant. If this does not happen, the O-rings dry out, and leaks develop.

It will take a good length of time for the leaks to develop, but it will happen, and then one summer, you'll find yourself saying that your A/C sucks because you didn't take care of the system.

Just look at older cars, and how much their systems leak, one of the major differences is using the compressor in the winter.

[MTBguy]

Running the AC while in defrost removes the moisture from the air that is being blown over the windshield so that it drys it off faster.

[xproductionz]

haha ..i thought the same thing long time ago when i first got my civic (which is an 01 and does the same thing)and ran some tests of my own... something you should try to prove to yourself why the a/c goes on.. when the car is all fogged turn the adjustment knob to the feet only and turn the heat all the way up and the fan all they way up... now see all the fog on on your window...of course just let it run for a while like this...and make sure your side vents are pointing to the side windows... you could probably do this while your driving or something...then turn the a/c button on and let it run till there is no fog on your windows....now if you were to turn off the a/c button again you will see that it starts to slowly fog back up again... the a/c button is basically what the past couple of posts said...it dehumidifies or removes the moisture from the air as it comes into the car...

[GScivic7]

Yah, a lot of people don't know that AC is just a dehumidifier, I found out just a few months ago.