justin218

I've had this problem with my AC for a few months now:

Turn car on, AC will blow hot. I'll turn off the AC, then turn it back on. This will then maybe work, or I'll have to do it a couple times, but eventually the cold air just starts coming out. Like it was cold the whole time but not being diverted right.

Unfortunately its at the point where its being very finicky to blowing cold though.

Could this be the changeover/heater valve problem as in this great DIY https://mbworld.org/forums/e-class-w...rol-valve.html ?

Thanks for any help or ideas!

Plutoe

Could be alotta things---find someone with DAS Xentry(diagnostic tool) and have the AC and car scanned to find the problem--then fixt yourself!

justin218

The only place I know of that would have that is the dealership? I'm in the Miami/Fort Lauderdale area if anyone knows of another place. It's an 08 E350.

Heatwave

It sounds like the same thing my '07 E35 does: occasionally and unpredictably while driving along it seems that all the a/c vent control doors have closed and no chilled air is blowing out the vents. I can hear the fan running beneath the dash, but no air comes out the vents. If I stop the car, turn the motor off, then restart it, the a/c vents open properly and everything works as it's supposed to. After reading the post about the heater changeover valve that you linked in your #1 post in this thread, I think I know what the problem may be.

klvaleri

Mine does it the same as you guys stated, first start the car with AC on, It blow warm out and couple minutes than cold comes out. I didn't pay any attention to it before but now starts to bother me because of first warm air blasting out. Is this normal for our car? Any suggestion would appreciated.
Thanks.

Jt Adams

I have a 2011 S550 and my A/C does the same thing. When I start the car and the A/C is on it will first blow hot air out the vents, but shortly after starting the car the cold air comes in.... I didn't know others were having this same problem.

Plutoe

If you are talking about starting from a cold start on a very hot day,your expectations may be to high--it will take awhile to get the cabin to the temp you selected---in any event get a small thermometer place it in the center vent----whats the temp--hopefully 42 degrees(F) after about 10 seconds!!

Tschuss_Bill

I've had this problem too, never solved it. It happens even in winter. When the car is warmed up, then stopped for 5 mins, 30 mins, whatever, upon startup, she blows hot for a solid minute. It could be 90 outside or 40, parked in the sun or in shade, it doesn't matter. It is as though the heater control valve opens when the ignition is turned off. On start up the SAM takes time to instruct it to close again.

Another note. If I park the car and leave the key in the ignition at position one, the hot blast at start up will not occur. Also if I turn the ignition to position 2 and wait for air to circulate and then start the car, the one minute hot blast is omitted. Lastly if I turn the key to position one and let it sit for a minute, then start, no hot blast either. methods 1 and 3 are not practical, but I do use method 2 in the summer.

Mine is a diesel. It's odd but I've learned to live with it. Oh, I don't mind the hot blast in the winter!!

PeterUbers

Same thing occasionally on 2014 e63S

Will run it by the svc advisor next oil change and report back

I have a vision.... The advisor is saying "everything working normally, keep an eye on it"

Lol... Svc advisors...

Tschuss_Bill

Ha! That's what they told me!!!!

Plutoe

"It is as though the heater control valve opens when the ignition is turned off. On start up the SAM takes time to instruct it to close again."

I regret to advise that if you are waiting for any of the SAM's to to do anything with the heater control valve, you might be better off to buy yourself a hot dog.

FYI your AC/heater control unit controls the coolant flow through the heater control valve.

Most likely you have one or more slow moving flap motors

Tschuss_Bill

Plutoe

I must have a slew of slow blend motors, because the heat blast comes out of the front console right and left as well as the front foot wells, both right and left. I have not checked the rear vents.

The heater duo valve is controlled by the left front SAM.

Tschuss_Bill

See this MB service document when SAM does not control the heater valve replace the SAM

(FWIW, I don't have this problem, the heater valve is controlled albeit slowly at start up. I don't know if my issue is with the SAM. But this is why I suspected the SAM)

Plutoe

That's for code 228 stationary heater---post you VIN and we will see if you have code 228!!---otherwise its not applicable

PS I changed my comments!!

Tschuss_Bill

I don't have a code 228 heater. The service bulletin that I attached was for a “cold air” problem. What the service bulletin does demonstrate is that the SAM has control function of the "heat exchanger shutoff motor (M16/32)". That is the duo valve. The duo valve for code 228 is nearly identical to non-228, it has the same single motor electrical connection, the difference is an additional hose fitting for the code 228 heater. (See attached).

As I said, the driver's side SAM has a role in the function of the Duo valve. There’s no shortage of discussion on this out there. Here’s one thread:
http://forums.mercedesclub.org.uk/sh...ad.php?t=77439
The SAM duo valve problems that I’ve found only relate to non-funtioning duo valve circuits, not delayed function issues. I don't know if my SAM is malfunctioning, or if it's something else. Swapping out the control unit in the dashboard is easy enough. I don't disagree, that item could be suspect.

Plutoe

You are confusing me again---if you say you drive 2005 E320CDI, and without a VIN, that means you drive either a 211.022 or a 211.026---neither of those cars have the old duovalve---what the 211.026 has is a Heat Exchange Shut off motor and yes that is turned on and off with instructions from the AC control module by the drivers side SAM.

However the more confusing part is that the context of this post is AC not the heating circuit which the shut off valve is apart of---has nothing to do with the cooling circuit.

Once again the driver has an issue with their flaps nothing to do with any of the SAM's

Tschuss_Bill

So the poster is saying the the climate control system does not control the heat exchange shutoff motor valve (and yes it is still often referred to as the 'duo valve')? I doubt that.

I disagree with your statement about the flaps. Those do not control heat, those only control air flow.

As per Bentley:
"regulates" implies opening/closing/and mid positions to control temperature to the heat exchanger

So in the dead of summer, with the temperature set to cool the cabin, upon warm start up, the heat exchanger shut off motor should not be open and take up to a minute to close correct?

I pose that question fully admitting that I don't know where the issue originates: the SAM or the dash mounted unit.

justin218

Well as an update to my situation (glad this drummed up some discussion above!) my AC has pretty much not been working lately, until I rev the engine to about 5k or so. Then it blows cold. Its worked 5-6 times just by revving the engine.

I have a noisy pulley somewhere in my engine, which I suspect is the AC compressor, wonder if it has anything to do with that.

irondad

Sounds like it might be the changeover/heater control valve.

Have you looked at this?

justin218

I thought it might be, but reading that thread I don't seem to have the same symptoms as that. That problem seems to have trouble turning on heat and/or having heat from some vents and AC from others. But I don't know, maybe it is my problem

Tschuss_Bill

I replaced my heat exchange valve, it made no difference. Another trick that I've tried is to hit the 'rest' button prior to starting the car. That reduces the heat blast to only a few seconds.

This workaround would not happen if the problem were defective flap motors, which has been suggested. Unwanted heat blast seems to be a controls issue.

Tschuss_Bill

AC from some vents and not from others. That wasn't what you originally described. You may be low on AC coolant/134a. Take it to a dealer or indy to have codes read etc. topping off with 134a is not a DIY in these cars.

Lonpe

I had the same problem. Took iT to an AC specialist.
The problem was solved by replacing the battery.
Mercs need à special battery that delivers About 50% more current as à normal one.
When the computer checks the current it detects à low current from the non stock battery, and iT begins to shut down the comfort functions. Including the AC.

klvaleri

Lesion learn and very interesting method for our car even though the car running OK. I have to check my battery to see if it is OK.
Thanks.

justin218

That is really interesting, I actually am on my original battery (nearly 8 years old now) and am going to replace it this week. I've noticed the engine has been struggling to turn over occasionally and figured its time.