sbsyncro

I just noticed on a 2-hour drive that despite the fan blowing at full volume, there was very little air coming from my vents. I tried turning the Auto on and off, tried manually overriding the fan (down and up) and also tried turning the recycle button on and off. None seemed to have any effect. AC button was lit the whole time. It was a warm day and in Auto mode the fan motor was running hard to try to cool the car to no avail.

It almost felt like there was a blockage, but there was very little air coming from either of the center vents or the window vent on the driver's side or pax side. (And yes, all the wheels were in the open position).

I did not feel air being blown from the defroster vent nor the footwells, so its not being diverted, as near as I can tell. AC was also not blowing very cold, but that might be a different issue, since the system may be in need of a recharge (it hasn't been touched since new)

Any ideas?

2006 E500 standard model w/NAV . 56,000 miles.

Thanks!

mtrevelino

The ac evaporator froze up. This is caused by low refrigerant. Once the car sits for a couple of hours, the ac will blow full force until the evaporator freezes again. This usually happens in humid conditions.
Mike T.

sbsyncro

Thanks Mike. I know that can affect the coldness of the air, but didn't realize it would also reduce the airflow?

Also, is there anything special or tricky about recharging the refrigerant in the E500 versus other cars I've done? (always have to ask about VW, Audi, BMW, Porsche, and Mercedes cars...) :-) . Normally I just use something like one of these kits:

jimbo1763

I have had similar symptoms on my E350. No air conditioning in the Georgia summer is a big problem. While punching buttons to try to get it going, I happened to hit the dedicated defrost button, and to my surprise air started to flow up to the windshield. I then turned off that function with the same button, and the air routed through all the vents like it should. This has worked for me on a couple of occasions. I have no idea what the issue is or why the procedure got the system going, but it's easy enough to try in a pinch.

Not a very sophisticated suggestion, I know. But it worked for me. In my case, the occurrence has been sporadic enough that I have not had to drill down deeper as to the root cause.

mtrevelino

some say there is an exact science to fill the system. I do it the wrong way and just add a half a can when my vents stop blowing air like with yours. It will usually get me by two years before I need to add another half a can.
Mike T.

sbsyncro

If its still acting up, I'll try that. I tried manually redirecting the airflow, but didn't hit the dedicated defrost button. I also remember seeing online somewhere a process for "resetting" the AC system. Here it is :Reset Mercedes AC System

Good to know - thanks. Just ordered a couple more cans.

rapidoxidation

When the AC button is lit, the compressor is turned off, IIRC. At least that's the way it is on my car.
When you adjust where the air is supposed to come out, do you hear the air shutters moving inside the dash?
What kind of shape is your cabin filter in?

sbsyncro

I could hear the mechanical parts moving when switching air sources, but not feel airflow from anything. I literally just replaced the cabin air filter last weekend with an OEM unit. The one I replaced was still in very good condition.

I'm thinking a frozen evap unit is the likely culprit due to low refrigerant (this car doesn't get driven much, so it has probably lost refrigerant due to age and drying of seals, etc). I'm going to test it today and see if the AC function is restored, and if so, I will consider that to be the solution. If not, I'll report back!

Thanks to everyone for the helpful posts so far! I stopped working on my own cars about 15 years ago, but this car and a teenage son I want to teach have both renewed my interest and enthusiasm for wrenching on cars.


Valve Cover gasket job

Gotta love that redneck work table. Haha

mtrevelino

If the car sits overnight and everything blows ok during the first 20 minutes of driving, it is the evaporator freezing up.
Mike T.

kajtek1

Older models don't have AC button, but EC(nomy) button that works this way.
AC button on means compressor is on.
It is common that on aging cars HVAC flaps start to stick. Older models had them vacuum-operated and it was quite a task to replace the elements.
From what I know, W211 has electric servos, what might be better, but still with limits.
I'd have to double check, but I remember that one of my $150 scanners had flap testing procedure.
But starting with base thing- cabin filter comes to mind.

sbsyncro

Just took it for a spin. AC blowing cold, and air flow from ducts seems restored. Likely culprit sounds like evaporator freezing up, even though I'm in So Cal and its not really "humid" here. A recharge is in order, it seems.

ygmn

IF low on refridgerant then you have leak...

why not fix leak first?

sbsyncro

hmm.... after 13 years and very little use, I’m not surprised that it needs a recharge. I’m not certain it means that it has a permanent leak that is significant enough to warrant a very expensive diagnosis and repair. (?)