AC not removing humidity - PeachParts Mercedes-Benz Forum

bnaquin · #1 07-08-2008, 11:32 AM

I've noticed on high humidity days or when it's raining, my AC doesn't seem to cool as well. The air from the vents feels cool, but it's not removing the humidity. The AC works very well on hot, dry days. Any ideas regarding what the problem might be?

'83 300D running R-12.

vstech · #2 07-08-2008, 11:59 AM

for a/c to remove humidity it must be running, draining, and circulating inside air. if you are not dehumidifying you are not doing one of these things. is outside wet air getting in?
is it cooling too well? perhaps add in a little heat to make it work a bit harder.

bnaquin · #3 07-08-2008, 12:05 PM

Quote:

Originally Posted by vstech

for a/c to remove humidity it must be running, draining, and circulating inside air. if you are not dehumidifying you are not doing one of these things. is outside wet air getting in?
is it cooling too well? perhaps add in a little heat to make it work a bit harder.

The heat function works fine and will remove fog from the windshield. I can't say if outside air is coming in or not. All I know is that when it's hot and dry outside, the AC is pretty darn cold. When it's raining or very, very humid, it doesn't cool the interior and feels clammy. Does the AC system dryer actually "dry" the air? Could this be the issue?

Jetmugg · #4 07-08-2008, 12:16 PM

The A/C system reciever/drier is only for the refrigerant/oil that is circulating internally in the system, it has no effect on the interior of the car.

Have you checked if the evaporator housing is draining properly? The rubber "flap" type of drains can easily become clogged with all kinds of crap, resulting in trapped humidity which will be felt in the cabin.

Otherwise, as long as the evaporator is below the dewpoint of the surrounding atmosphere, the moisture will be removed and will drain away. A good strong blower helps, by keeping the air moving past the evaporator.

SteveM.

Jeremy5848 · #5 07-08-2008, 12:17 PM

Air conditioning (refrigeration) removes humidity from air by cooling the air. Cool air can't hold as much moisture. The water vapor condenses out as liquid water and goes out through a drain. It is possible that your drain is plugged up. preventing the water from exiting. That would allow at least some of it to re-evaporate and "contaminate" your nice cool dry air.

Caduceus · #6 07-08-2008, 12:20 PM

As moist air passes over the evaporator it condenses on it into a frost. So if it was able to remove all the moisture from the air it would ice up really fast and lose effectiveness. So when it cycles off the condensation drains off of the evaporator and drains from the car. Ultimately some off the humidity from that process will be transferred to the air moving through it and back into the cabin. So if a component isn't working in the system it could not be cycling properly and either building up too much ice on the evaporator or not enough of a charge and it isn't cooling enough thus the moisture is just condensing and almost humidifying the cabin. One cause could also be if your recirc/fresh air flap is stuck on outside air all the way. It would be alosing battle to remove that much humidity from the air.

vstech · #7 07-08-2008, 12:24 PM

ahh, not cooling well when it's clammy out. this is not unusual.
latent heat is removed by condensing humid air. the a/c system can only remove a specific amount of heat. high humidity air has 4 to 10 times the amount of heat as dry air. and you will notice it in the reduced cooling output. it just takes more time to cool the car with high humidity... sorry. clean condenser, clean evaporator, clean drain, clean blower wheel, make sure the fan is on as high as it will go, make sure the outside vent is closed, have it on recirculate. and have a little heat mixed in to keep the windows from fogging on the OUTSIDE...

vstech · #8 07-08-2008, 12:30 PM

Quote:

Originally Posted by Caduceus

As moist air passes over the evaporator it condenses on it into a frost. So if it was able to remove all the moisture from the air it would ice up really fast and lose effectiveness. So when it cycles off the condensation drains off of the evaporator and drains from the car. Ultimately some off the humidity from that process will be transferred to the air moving through it and back into the cabin.this is how a freezer works... not a car a/c... unless the charge is low, or the blower is not running well... or it's really cold in the car... So if a component isn't working in the system it could not be cycling properly and either building up too much ice on the evaporator again, only freezers work this way. not car a/c's or not enough of a charge and it isn't cooling enough thus the moisture is just condensing and almost humidifying the cabin. this is just wrong...One cause could also be if your recirc/fresh air flap is stuck on outside air all the way. It would be alosing battle to remove that much humidity from the air.this part is right.

sorry to tear down your post, just trying to put in correct air conditioning answers...
low freon pressures would actually cause ice.

Caduceus · #9 07-08-2008, 12:37 PM

Ahhh So that's what was wrong with my old car. Well glad to be corrected.

bnaquin · #10 07-08-2008, 01:22 PM

I'll so some checking and post back what I find. The recirculation flap may be failing open. I've got an intermittent vacuum issue as it is. Maybe that's where the issue resides.

babymog · #11 07-08-2008, 02:06 PM

Recirc flap is a good place to start. Also, run the fan on high, the more airflow over the evaporator the more dehumidifying.

bnaquin · #12 07-08-2008, 02:07 PM

Yes, I've been running the fan on high and it seems to blow quite well.

Jadavis · #13 07-08-2008, 02:09 PM

Drain line is plugged. Do you get a puddle on the ground under the car on humid days? If not, then it is plugged.

-Jim

vstech · #14 07-08-2008, 02:24 PM

it sounds like it is removing moisture, it's just not cooling the car like he wants...
it's a fact of life. moist air cannot be cooled quickly without additional cooling capacity.

bnaquin · #15 07-08-2008, 02:32 PM

Yes, I get a pretty good puddle under the car from the AC.

Say, what's the best way to get to the recirculation flap and pod?