After starting, A/C blows hot air until driving...it's fine for the rest of the drive
 

After parking my car at work all day, the interior is very hot given that the ambient temp is in the upper 80's. However, once I start my car ('11 E350), the air conditioner blows warm air at full blast.....until I begin driving. I've sat for up to 10 min after starting and it continuously blows hot air....until I begin driving. Once I pull onto the road and reach 30-40 mph, cold air immediately begins blowing and it's VERY cold at that point. This isn't an idle problem I don't think because once the air begins to blow cold, it KEEPS blowing cold even at stop lights or at any subsequent idle situation. Even after driving to the grocery store and staying inside for over half an hour, the a/c still blows cold air once I restart the car with warm engine.

Therefore, the only issue is after the car has sat all day. I hear the cooling fans kicking in (the jet engine sound??) so I'm assuming they're functioning properly. Normally, I'd say this is just a characteristic of this car's a/c system but, this is my third E350 and I've just recently gotten out of a '10 ML350 and none of them behaved this way after sitting all day at work. Therefore, I won't accept the "it's normal for a hot car to act this way" explanation.

Full-disclosure, I've checked nothing on the car other than making sure the big fan up front is turning. Any thoughts or anyone have similar experiences?

Maybe the AC's freon needs a top up. I had similar symptom on a previous car and it was the refrigerant/freon in the AC system had leaked a little so it was a little low. Dealer topped it up and it started to blow cold air out within a few seconds of starting the car.

Once I start driving, today it was while I was still in the parking lot, I hear a very brief hissing sound then very cold air immediately begins blowing. Still sound like I'm a little low on freon? I'm clueless about AC systems. Thanks!

I would have your blend air door actuators checked, it could be a blend air flap sticking. My 2013 E550 will sometimes take a few seconds after moving before the defrost will start blowing air on the windshield.

Could be an issue with the clutch on the AC compressor. Could be a relay issue. I had a relay issue on a Honda and it was a cheap DIY fix, but it was easier on that car to observe the compressor engagement.

So the fact that driving corrects the issue every time, it could still be the blend door actuator or the AC clutch? As I said, I'm pretty ignorant when it comes to AC systems. Thanks again for the help!

The hissing is key; if you hear it, the system is expanding the refrigerant appropriately. It should be regular but intermittent. I would go with simplest solution, which is the refrigerant has migrated out of the system and now just low. Dealerships will insist they are sealed and should not leak, and try to charge you for a system flush and stuff, but over time, the refrigerant will migrate out of the system as a matter of course. If they top you off and the problem persists, then I'd look for something more extensive.

These are hard to diagnose. I keep a cheap refill kit around to test pressure but you have to make sure the compressor is running. If you can see the compressor pulley you should be able to tell if the inner clutch is turning or not.

I have the same issue but didn't try driving yet. It's hot forever unless I turn the engine off and on again. Then the air is really cold. What's up with this anyway?

Thanks, I'll try that.

I will put a set of gauges and check pressures. Might be as simple as low on refrigerant, Condenser fan not working to cool it off so once you start driving the air cools it off enough for the high pressure valve to open up, or other more expensive things. But will start with checking the pressures.

This is the time of the year, when we have 10 paralel topics about AC.
There is pretty easy procedure to troubleshoot the system and I had it posted 100 times already.. .maybe 200 ...
So here it is again http://www.mercedesmedic.com/ac-air-...le-codes-list/
For W212 you need to get a scanner who can read the values as MB no longer makes it option on car displays.
Once you have 2 sets of sensor readouts, post them here and we will help with interpretation.