Has anyone combined the fresh air and AC systems?

[wrinkledpants]

The fresh air blower is loud since it's sitting right there, and honestly, I can't ever think of a time when I'd want to use it (and never have). In looking at the AC plumbing, it seems like I could almost plumb the AC outlets into the fresh air circuit, and just remove the fresh air fan. Then, maybe find a way to turn the AC fan on without the AC clutch coming on. This is what I see as the benefit:

- AC directional control instead of just out the vents
- AC fan will be quiet when used as the fresh air fan
- Can open up fresh air wide open on the HWY for ram-air affect without having the fan on
- Can turn the AC fan on with the heat to keep good air movement through the cabin without having the loud footwell blowers going. Sometimes, I just need a lot of air movement to keep the condensation down on the windows without roasting the place out.

Am I missing anything here?

[wwest]

Originally Posted by wrinkledpants

The fresh air blower is loud since it's sitting right there, and honestly,

I can't ever think of a time when I'd want to use it (and never have).

I have often found it usefull in the wintertime, along with lowering the windows slightly, to help remove interior window/windshield condensation. And keeping a bit of fresh air flowing into the cabin in cold weather will always help prevent window/windshield condensation.

But that was with my '78, the BOOSTER fans in the '88 make window/windshield condensation a non-issue.

In looking at the AC plumbing, it seems like I could almost plumb the AC outlets into the fresh air circuit, and just remove the fresh air fan.

Now that I more clearly see your goal, low noise alleviation of window/windshield fogging, it seems to me that you would be better served by plumbing the fresh air source into the A/C evaporator plenum inlet.

That way you could still make use of the OEM method of keeping the windshield clear of condensation, low volume HEATED airflow to the defogging/demisting ducts, while also continuously purging the cabin of moisture laden atmosphere.

Then, maybe find a way to turn the AC fan on without the AC clutch coming on. This is what I see as the
benefit:

- AC directional control instead of just out the vents
- AC fan will be quiet when used as the fresh air fan
- Can open up fresh air wide open on the HWY for ram-air affect without having the fan on
- Can turn the AC fan on with the heat to keep good air movement through the cabin without having the loud footwell blowers going. Sometimes, I just need a lot of air movement to keep the condensation down on the windows without roasting the place out.

Am I missing anything here?

Condensation....

Fresh air flowing continuously through, into and OUT the cabin is absolutely the best method for abating the formation of condensate on cold interior glass surfaces. My '92 LS400 had 2 "extraction"/puller fans I mounted in the trunk for exactly that reason. Low NOISE too.

[Iciclehead]

I personally like the two systems although they are not anywhere near perfect. I just wish I could find a real good motor for the fresh air system (e.g. like one out of a Honda or something with REAL electric motors, not this Bosch crap). Little stronger, lot quieter would be nice. But then again, it probably comes down to fan design, and if you look at the actual fan, it doesn't look like a high performance/low noise kind of thing...

Dennis

[wrinkledpants]

yeah, my beef is the noise. It's annoying that I have to have the electric fan on full speed just to have the fresh air vent open all the way. Ideally, I'd like to be able to keep the AC system a closed circuit by having the fresh air closed, but have the option of having the AC system an open circuit where it pulls in fresh air to blow over the evaporator. My AC system has plenty of cooling power to do that at HWY speeds. I'd just close it to recirculate when I'm in the city. I don't need a fresh air fan when I have plenty of heating power, and plenty of cooling power.

[kuehl]

Originally Posted by wrinkledpants

The fresh air blower is loud since it's sitting right there, and honestly, I can't ever think of a time when I'd want to use it (and never have). In looking at the AC plumbing, it seems like I could almost plumb the AC outlets into the fresh air circuit, and just remove the fresh air fan. Then, maybe find a way to turn the AC fan on without the AC clutch coming on. This is what I see as the benefit:

- AC directional control instead of just out the vents
- AC fan will be quiet when used as the fresh air fan
- Can open up fresh air wide open on the HWY for ram-air affect without having the fan on
- Can turn the AC fan on with the heat to keep good air movement through the cabin without having the loud footwell blowers going. Sometimes, I just need a lot of air movement to keep the condensation down on the windows without roasting the place out.

Am I missing anything here?

No, you pretty much have it covered. I'm sure there is a thread in PP on what you wanna do. You could just roll down the window. Or play with the annoying slider controls. But, if you attempt mix outside air that is moist then chances are it 'could' freeze up on the evaporator coil if you have your thermostat set to max cold because the enters the bottom of the coil while the evap fan pulls it up so the water wants to hang on the fins. I'm sure 'some one' will have a lot to say on this, lol.

[wgirardot]

Originally Posted by wrinkledpants

yeah, my beef is the noise. It's annoying that I have to have the electric fan on full speed just to have the fresh air vent open all the way. Ideally, I'd like to be able to keep the AC system a closed circuit by having the fresh air closed, but have the option of having the AC system an open circuit where it pulls in fresh air to blow over the evaporator. My AC system has plenty of cooling power to do that at HWY speeds. I'd just close it to recirculate when I'm in the city. I don't need a fresh air fan when I have plenty of heating power, and plenty of cooling power.

My fresh air blower doesn't work, but I still use the venting levers to regulate amount of fresh air coming in while driving. Sometimes in combination with the a/c on to regulate temps even more. Just pull the plug on the motor and try it out.
Still 2 seperate systems. With heat, three seperate systems.

Bill

[wwest]

Originally Posted by kuehl

No, you pretty much have it covered. I'm sure there is a thread in PP on what you wanna do. You could just roll down the window. Or play with the annoying slider controls.

But, if you attempt mix outside air that is moist then chances are it 'could' freeze up on the evaporator coil if you have your thermostat set to max cold because the enters the bottom of the coil while the evap fan pulls it up so the water wants to hang on the fins. I'm sure 'some one' will have a lot to say on this, lol.

Kuehl, don't jump for the boat, it's already to far from the dock.

Insofar as keeping the windows/windshield from fogging over during the winter months there is primarily ONE base cause...HUMAN METABOLISM...

In a closed passenger cabin the atmosphere's Rh level climbs and climbs due to our breathing and persiration. At the same time the glass surfaces, especially the windshield are being CHILLED due to the cars road speed.

Two things are needed to best alleviate the problem of windshield condensation while also maintaining the cabin at a reasonable human comfort level.

1.) A method to continuously exhaust the cabin atmosphere and thereby alleviate the inssue of continuous RH build-up. That, of course, also means a way is needed to bring FRESH airflow into the cabin.

2. A method for continuously WARMING the interior surface of the windshield such that it does not decline to the dewpoint of even the incoming FRESH low Rh airflow.

And now without the NOISE associated with the 911 fresh air intake method.

With my '92 LS400 I simply mounted two "sucker" fans in the trunk (can't be heard) to blow air out of the vents at the bottom of each rear quarter panel. The LS already had ports for exhausting the cabin atmosphere into the trunk area. In that way the climate control systems use could be restricted to simply moving low volume slightly warmed fresh inlet airflow to the interior surface of the windshield.

What OP is asking for is a way to duplicate my LS400 solution but with the restrictions, modified restrictions, of the 911 system.

As I have said, in my '78 that often mean having the windows lowered slightly and the 911 HEAT going FULL BLAST to the interior windshield surface. Not very comfortable having that HOT airflow to the windshield REFLECTED directly to one's face.

But we survived.

The Bible...

http://www.nettally.com/palmk/Defrost.html

[wrinkledpants]

With all due respect, if you have to add sucker fans to your LS than it must have either had issues, or was a weak system. My 87 Accord would keep the frost off the windows down to -40 F. My Audi could keep the condensation off the windows when it's 100% humid outside, and the inside is packed full of wet, snowy skiers.

The 911 has enough fans to get a good flow going, it's just that with the current design considerations, and what I'd like to accomplish, that flow comes with some tradeoffs. I've already got 8 fans on this car. That last thing I want to do is add more of them.

[r-mm]

Interesting concept.

Can anyone clarify why Porsche set up the fresh air system so that the ventilation knob engages the ventilation fan when you have it all the way open? Why force this combo?

[wgirardot]

Originally Posted by r-mm

Interesting concept.

Can anyone clarify why Porsche set up the fresh air system so that the ventilation knob engages the ventilation fan when you have it all the way open? Why force this combo?

maybe that was "poor man's a/c" back in the day. There are actually 2 lesser fan speeds as the vent opens up to full open/full fan speed