jtse

I've got 156,000 miles on my ML and i've noticed my A/C isn't working properly all the time. When I'm in a idle for like 20-30 sec. for say a red light, my A/C would be not cold at all, and because i live in a hot area, around 100F almost all the time during summer, this problem is making me sweat everyday like crazy whenever i start the car till i hit the freeway, and that sucker starts to cool down once the engine runs for like 30 secs.

So I was wondering if any of you know what is up, and what i can do to fix this problem?

Thanks in advance!

sosh

Could be lots of things; bad aux fan (not coming on), bad compressor, low on refridgerant, etc. Best have it checked out by a dealer or a good A/C shop.

OttoBon100

You don't say what year your ML is but if it is an older one they still had "sight glasses" near the front close to the radiator going to the condenser. If your model has one look into it while the AC is running. You should see liquid freon - or lots of bubbles if it is low on freon - running thru it. No movement at all of anything means you have another problem as stated by sosh. I'm not sure what year the sight glasses disappeared. You rarely see them on newer cars. They helped DIY'ers charge their own systems when Freon 12 was still used. You added freon until the bubbles went and away and then stopped charging. Now to do it correctly without one you pretty much have to have gauges to ensure you don't overcharge the system.

buzzbe

I just had same problem, turned out to be the30 amp fuse under the hood. I think it was #44, however it is marked on fuse index a/c fan...

AndrewAZ

When its over 100F not to many cars can keep cool at lights. I have an 02 and just had the refrigerant replaced and it blows colder than before but it still warms up when at a stop light. If I got for a drive on the freeway it gets very very cold, but around town if I am not going 50-60 mph its not cold, when I get pulled over for speeding my excuse will be "just trying to keep cool"

sosh

If your ML will not keep cool at an idle while stopped you too have a problem!! I have never owned any airconditioned car that does not maintain its cool temp while idling, even idling for an extended period of time in the hot sun.

AndrewAZ

You dont live in a state where 115F is the normal everyday temperature and it only cools down to 100F at night. Even my small cabin of the M3 it does not get cold unless I drive on the freeway. Now you have to realize 115 is air temp ground temp is going to be 150F+ so stopped the car is basically sucking in 120-130F heat. The car does not blow hot air when stopped it just doesnt blow cold air like it does when driving over 50 MPH.

CoolHandz

Hi all,
First off what a wonderfull forum very informative and fun to read.I'm new here and I have a question.I Live in SaFrancisco so it's very rare for us to use our A/C.I took a trip up North Sacramento where it hit 112f when I noticed that my A/C was not really getting cold.When I got back I added an out of the shelf refrigerant so I know my A/C is full.When I drive around areas below 100f my system blows cold air so I thought all is well.Last weekend I decide to drive to Vegas and there it hits.When I got to areas over 100f and full blast my A/C the system blows HOT air and it will not blow cold even if you turn it on or off.I noticed that if I restart my engine and start low it starts to blow cold air up to level 3 then blows hot air at high fan settings.One thing I notice at idle at full blast my idle goes up and down.A/C motor goes on and off.What do you think is going on?Can it be a sensor or bad A/C motor.My truck has 54000 on it I only use it for long drices.
Thanks

jtse

well my car is 2000 ML320 and it as 157,000K on it. I called mercedes and told me that if my freon's are gone than the car would not be cool at all. From where I live, my car is in 100F almost all the time, and its driving me nuts to go through local town sweating like a pig. I went to the A/C shops and they said they can add freon for like 70 bucks, I'm not sure, What do ya guys think?

OttoBon100

That is much cheaper than Benz will do it for you. Hopefully they will diagnose the problem first. Just adding freon to a system that is leaking will be throwing your money away. You'll be right back having it charged again.

sosh

First off your car does not use Freon. Secondly, if it needs refridgerant it has a leak which must be addressed first. $70 bucks will not cut it to repair correctly.

OttoBon100

Well, basically what sosh told you is what I already said. For those of us who have been in the air conditioning and refrigeration business - quite awhile ago I worked in that business for 15 years - we still refer to it as Freon. The term "Freon" is actually a trade name used for refrigerants made originally by Dupont but there are a number of companies that produce it and so "Freon" became a generic name used by those in the trade for all refrigerants. That term is still in very common use today by techs and novices alike. Technically the new refrigerant used currently in cars is HFC-134a and is Tetrafluoroethane. The refrigerant used in older cars - I know my '92 190E still had it - was "CFC-12" or "R-12" and was Dichlorodifluoromethane. We "older" techs still refer to them all as Freon - easier, don't you think??? Much more than you ever wanted to know, huh? Good luck in getting it fixed.

jtse

I got it fixed. And I did it by myself. I read the post above about the 30amp fuse, and that was it. I didn't believe it, the green little fuse was black in the middle so i took the good one that opens the Sunroof off ( because my spare was no where to be found...) and put it in, and Voila, it Worked. I am pretty happy right now, cause, its SO HOT here. Anyway, Thank you so much guys.

oh yea, Where can I get a 30Amp Fuse? is the dealer gonna charge me if I go?

OttoBon100

Great! Any car parts store; e.g., AutoZone, Pep Boys, NAPA, etc.. Look in your fuse box too, mine had a couple extra fuses although I don't know if one was a 30 amp.