How is Fresh Air getting in?

[mooney265]

Just recenlty went with Griffiths [Charlie] and changed out 3-condensers, evaporator and added more powerful blower motor. The A/C has been working great. I'm getting 35* drops in temp over the evaporator.

One problem, however, is when i'm cruising at highway speeds - I'm getting too much O/S air in - I literally feel the humidity rise by the second has I hit the interstate. I've gone so far as to plug up the front intake vent.

I have all of the levers [3] moved to the far left position and my heater boxes are definitely closed.

Where else could this "ram air" be coming from? Any suggestions... Thanks

[na2ub]

If you front trunk doesn't seal perfectly, air gets rammed in and makes its way to the passenger compartment without too much trouble.

[mooney265]

Originally Posted by na2ub

If you front trunk doesn't seal perfectly, air gets rammed in and makes its way to the passenger compartment without too much trouble.

I could buy that - - because it's only happening under high speeds... I never would have even considered that - - I'll have to figure some way to test this [maybe tape the hood down with painters tape and take for a quick spin].

What else?? Thanks

[pete3799]

Could be bad foam gaskets (on the flappers) inside the fresh air blower housing.
If it's a euro like mine they only have 1 flapper in there. No idea why but I've always got fresh air coming in even with the lever all the the way to the left.

[mooney265]

Pete,
Thanks for the reply. I forgot to mention that I disconnected the blower hoses coming from the "flapper assembly" and stuffed cleaned shop towels in the hoses and still was getting O/S air in there.

While I was "stuffing" i took note of the foam and flapper [both of them] and noticed that they were fully closing and good foam still remained...

Thanks, Shannon

[mooney265]

This was never a problem when i didn't use my A/C for the past 4-yrs of ownership...

[Flat Six]

Originally Posted by mooney265

This was never a problem when i didn't use my A/C for the past 4-yrs of ownership...

Longshot, but the evaporator fan might also be pulling outside air from under the car via the drain hole in the evaporator box. R&R'ed my evap a couple of weeks ago and was stunned at how big the drain pipe is -- about 1/2" diameter.

Crawl under the car and temporarily put a little tape over the drain hole to test?

HTH

[mooney265]

Originally Posted by Flat Six

Longshot, but the evaporator fan might also be pulling outside air from under the car via the drain hole in the evaporator box. R&R'ed my evap a couple of weeks ago and was stunned at how big the drain pipe is -- about 1/2" diameter.

Crawl under the car and temporarily put a little tape over the drain hole to test?

HTH

Great Idea! The value of this forum...

I DIY'd the entire A/C system -- so, pretty familiar with that drain line - - will do the test...

[aj88cab]

Just a thought...it might not be coming from the front. Check you heater flapper boxes. Make sure they are closing and that the butterfly seals are good.

[wwest]

Originally Posted by mooney265

Just recenlty went with Griffiths [Charlie] and changed out 3-condensers, evaporator and added more powerful blower motor. The A/C has been working great. I'm getting 35* drops in temp over the evaporator.

One problem, however, is when i'm cruising at highway speeds - I'm getting too much O/S air in - I literally feel the humidity rise by the second has I hit the interstate. I've gone so far as to plug up the front intake vent.

I have all of the levers [3] moved to the far left position and my heater boxes are definitely closed.

Where else could this "ram air" be coming from? Any suggestions... Thanks

May actually be SOP....

"..more POWERFUL blower motor.."

The evaporator fan/blower is pulling/sucking airflow UP through the evaporator vane surfaces. The A/C DEHUMIDIFIES that airflow via cooling it as it flows through the evaporator vanes and CONDENSES onto those vanes. At lower, low, blower speeds as the condensate film grows it forms droplets which run down the face, vane surfaces, of the evaporator and out the drain "tube".

HIGH, Higher blower speeds and guess what....?

Upward airflow "force" overcomes gravity and before the condensate gets to the droplet stage the condensate "flows" into the cabin.

On a HOT and HUMID day you might ever observe "cloud" formation, water droplet formation, right at the COOLED air cabin outlets, as the slightly compressed ("restricted" duct path volume/CSA) system airflow, SATURATED airflow, reaches an area of atmospheric pressure, the "open" cabin.

If your evaporator blower speed is "just" high enough then the air flowing through the evaporator might well be cooled just barely to the point of condensation. Now the "final" condensation will occur as the "compressed" system airflow expands as it reaches atmospheric pressure.

[Por_sha911]

A poorly sealed smugglers box will bring in outside air but the fact that it happens at speed points to the trunk seal.

[DRACO A5OG]

Not for nothing but how are the heater flaps below, are they full operational. Have a helper open and close the levers and see if they open and close all the way.

One of my flaps were not functioning properly and while at speed I was getting OS air from the side vent even after closing the front fresh air inlet. Fixed the flap and no more OS air in the cab.

[911pcars]

Front of car = high pressure area. Trunk seal.

Completely fill the trunk with your unwashed laundry, then road test. Note: This is not a suggestion for a permanent fix.

Sherwood

[mooney265]

Originally Posted by 911pcars

Front of car = high pressure area. Trunk seal.

Completely fill the trunk with your unwashed laundry, then road test. Note: This is not a suggestion for a permanent fix.

Sherwood

Mr. Sherwood: you gotta deal! This trunk lid thing just keeps coming up. When the weather calms down, I'll tape the sukker-shut [with painter's tape] and take her for a spin...

That should tell me what I need to know - Thanks!

[Flat Six]

Originally Posted by 911pcars

Front of car = high pressure area. Trunk seal.

Completely fill the trunk with your unwashed laundry, then road test. Note: This is not a suggestion for a permanent fix.

Sherwood

So if you get that funky dirty laundry smell in the cabin that'd confirm trunk leak? There has to be a less painful way to test!

[mooney265]

I'm going to go ahead and order/install a new hood seal.

In the meantime, is there a way to adjust the hood down [even tighter] when latched?? I"ll do a search...

[86 911 Targa]

Originally Posted by mooney265

I'm going to go ahead and order/install a new hood seal.

In the meantime, is there a way to adjust the hood down [even tighter] when latched?? I"ll do a search...

Careful, careful not to overtighten your hood latching mechanism causing excess strain on the hood release cable.

Bad times will ensue if that cable breaks. (do a search).

Good luck,

Gerry

Here's an old post.

[Flat Six]

Did you ever figure out where the unwanted air is coming from?

[wwest]

Originally Posted by mooney265

I'm going to go ahead and order/install a new hood seal.

In the meantime, is there a way to adjust the hood down [even tighter] when latched?? I"ll do a search...

Air, air pressure, atmosphere, within the trunk area CANNOT enter the evaporator plenum UNLESS the footwell inlet plastic air duct from the cabin has been removed or modified.

You're simply CONDENSING the atmospheric humidity into droplets as the airflow, UPWARD flow, passes through the evaporator TOO FAST to condense ONTO the evaporator vanes.

Slow the blower down, way down, and let the atmospheric humidity condense onto the evaporator vanes. And absent the torrent of air UPFLOW the condensate will eventually form into large enough droplets for gravity to overcome viscosity and the water will drain away.

[mooney265]

Originally Posted by Flat Six

Did you ever figure out where the unwanted air is coming from?

I put this off for a while and worked on other items on the car: exhaust and brakes. Got back on it this month...

And, changed the front trunk seal and still have the problem. Will tape the hood shut and do a test run - - should have done this months ago...

I'm under the gun to get the car "long trip" worthy, as I'm driving from New Orleans to Austin for the F1 event next month.

The A/C works great at low city driving speeds but is terrible over 50+ MPH!! It's got to be air getting in past the trunk seals!!

I'll try to get this done on the upcoming weekend and report back. Thanks for all of the replies!!