HVAC system issue

So I posted this back in January and it's rearing it's ugly head.

This is mainly on driving trips of 2hrs or more. What happens is the vents internally close very slowly, limiting the air discharge from the vents. The odd thing is the fan remains at the same speed (I.E. I can hear it at the same speed). If I shut the system off for 10 mins, and restart the fan it'll come back to normal, the fan will blow normal speed thru the vents. but again, the airflow will slowly decrease after a while.

is there a solenoid or something internally that could be failing? I mean, if i set the system on auto, the fan speed will increase but the flow won't because the vents just aren't allowing it through.

And the sensor is hot (the one on the dash) because the sun is shining right on it.

It's gettin to ticking me off, this HVAC system. I mean, when I shut it off, if I want the windows open, I can't just shut off the system and put recirc on, it ONLY allows recirc on when the system is on. I love the car, but I think the HVAC system was poorly designed with too much internal control for no reason whatsoever.

And since summer is coming and I'll be on the road for work a lot more, I NEED this figured out. I can't run in the car on the interstate with the a/c off for 10 mins at a time in a suit while the damn system resets or whatever! HELP!

So, you have a climatronic system yes? When the system starts to lose flow, is it attempting to change the air temp? For example, is it trying to blend a colder charge into the air vents?

Nope, i keep the temp the same. Yes, climatronic.

The fan works at the same speed, it seems like an internal motor is slowly closing the vents to limit flow for some reason, and that's not using the auto setting. using the auto setting increases the fan speed, but the flow from the vents remains unchanged.

Ok basics:
1. Has the cabin air filter been changed? When, if ever?
2. Does the condition only occur with recirculate off?
3. Is there any leaf litter/debris at the base of your windshield?
4. Does changing the air direction (defrost, foot wells, main vents) make the symptoms better or worse?

-yes
-yes as far as I know
-nope
-doesn't affect it, the amount of flow remains the same. It's like there's a valve or something a the fan discharge that closes to minimize the flow for some reason.

Best thing to do before having to tear into the system is hook up VCDS and run functional tests on the HVAC system. You may even have CECM fault codes regarding the HVAC stored and waiting to tell you ,"Hey I already know what's up!" If your motor theory is correct, perhaps two doors are conflicting and basically causing the system to internally loop or plug itself up. Without having torn into one before, this is best guess info.

hm. I gotta find someone in my area with a vag-com then!

Anyone near Sarasota with a vag-com for the A5's?

What you describe can also be a simple low freon charge, causing icing up of the evaporator.

Keep searching for a local person with VCDS. If you cannot find one, try to get some local owners to go in with you to buy one.

It will pay for itself.

Your climatronic system will give a lot of information with VCDS.

DanG144 said:

What you describe can also be a simple low freon charge, causing icing up of the evaporator.

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My thought too.

easy enough, next time the air flow is down to nil crank the heat and see what it does, instant or gradual increase?

philip_g said:

My thought too.

easy enough, next time the air flow is down to nil crank the heat and see what it does, instant or gradual increase?

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Is the airflow always pass through the evaporator regardless of blend or temp settings?

Anomie said:

Is the airflow always pass through the evaporator regardless of blend or temp settings?

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I'm thinking it does. I believe the ac compressor runs when the defrost is on.

AHA! This is where it gets curious. We first noticed this on a trip to NC back in January. Left FL early in the a.m. with the a/c on. Once in SC, it got cold out, but the air flow issue was present. Cranked the heat on, and the airflow through the vents didn't increase. I posted something regarding this then, but once we were in NC we only used the heat, so we never had the problem again.

Could it be that the air passes the evaporator regardless of temp desired? I mean, air that was coming in was warm, but there was so little of it, it was ridiculous.

Air always goes through the evaporator. It is then directed through or around the heating coil.

So if it is icing, you turn off the AC, and let air blow through melting the ice, and air flow will increase.

Another tell-tale is a huge water puddle under your car when you park it and the ice melts.

Funny you should post. While we were having this issue we passed right by Chapin, SC.

So, sounds like I should have the r134a topped off for now.

I would suggest getting the VCDS info first, then if it still looks as if it is required, pull the charge and install a new one.

That's the only way you know you have the right amount of charge in it.

Just adding some freon can result in an overcharge, that can be harmful to your system.

yeah, I'd definitely have a shop do the r134a thing.

Stop by the next time you have a chance.

next time I'm on the way to NC I'll definitely let ya know.

chimmike said:

Funny you should post. While we were having this issue we passed right by Chapin, SC.

So, sounds like I should have the r134a topped off for now.

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it's relatively easy to do if you have an interest and you can do it right, unlike most shops.

philip_g said:

it's relatively easy to do if ... you can do it right...

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...which entails a full recovery and evacuation, leak test at 29.9" vacuum, fresh PAG oil and a proper R134a charge injected.

Granted with the more recent HVAC service machines, like the CoolTech by Robinair, the process is painless and almost brainless, but I've only come across a few of these.

Anomie said:

...which entails a full recovery and evacuation, leak test at 29.9" vacuum, fresh PAG oil and a proper R134a charge injected.

Granted with the more recent HVAC service machines, like the CoolTech by Robinair, the process is painless and almost brainless, but I've only come across a few of these.

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Why would you do a full recovery with no equipment failures and no exposure to atmosphere? There's no need. And if you're going to go completely overboard since you opened the system you need to replace the filter/dryer.

And why do you need a machine? A gauge manifold and a vacuum pump works fine.

philip_g said:

Why would you do a full recovery with no equipment failures and no exposure to atmosphere? There's no need. And if you're going to go completely overboard since you opened the system you need to replace the filter/dryer.

And why do you need a machine? A gauge manifold and a vacuum pump works fine.

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A low charge can be indicative of a leak, and I'm a firm believer of getting it right the first time.

Anomie said:

A low charge can be indicative of a leak, and I'm a firm believer of getting it right the first time.

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Yeah, I can see how 4 hours of labor is a lot better than $4 in gas every season.

philip_g said:

Yeah, I can see how 4 hours of labor is a lot better than $4 in gas every season.

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yeah it's cool, vent a known pollutant.

Anomie said:

yeah it's cool, vent a known pollutant.

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Yeah, 134a is deadly, that's why it replaced r12.

philip_g said:

Yeah, 134a is deadly, that's why it replaced r12.

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yeah, haha. R134a is as deadly and effective as r12

chimmike said:

yeah, haha. R134a is as deadly and effective as r12

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In the fact that R12 venting is like a gnat fart in a hurricane compared to other gasses, sure

philip_g said:

In the fact that R12 venting is like a gnat fart in a hurricane compared to other gasses, sure

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hey, I'm not disagreeing. I think the whole R12 thing was blown WAY out of proportion. I think it was more of a "hey, we make more money off R134a in production, can you guys ban r12 for us?"

chimmike said:

hey, I'm not disagreeing. I think the whole R12 thing was blown WAY out of proportion. I think it was more of a "hey, we make more money off R134a in production, can you guys ban r12 for us?"

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All of the refrigerant hoopla was horse shiz