RichDMB

When I turn on the AC it blows cold, but after about 7-8 minutes, it will start blowing warm and humid air. I can turn it off, then turn it back on and it's cold again but only for the same 7-8 minutes. This morning I changed the cabin filters as I've had the car for a month and there was a tiny bit of musty smell. Filters weren't that bad, and I sprayed the cabin filter compartment with lysol. I had bought a can of R134 thinking that I might be low, but before adding the 134 I hooked up the gauge to the low pressure side. Initially with the car not started, the gauge went into the red, but once I started it, it dropped right down to the 43-45 psi range. From what I gather, that's the sweet spot, so I didn't add any 134 as I know an overcharge is a bad thing.

Does anyone know what my problem could be? I don't have any means of pulling codes......gotta get me one of those diagnostic tools.

BOTUS

some common sense, (when explained to you) and a simple bit of economics

your domestic fridge is remarkably similar to the AC in any car - but has the parts fixed with copper pipes and solder so the gas says put, and the compressor seals sit happy with correct amount of daily exercise and in the good old days a design life over 30+ years. your car has a system with flexible rubber hoses and between these, the joints and not being used every day means the compressor seals also deteriorate, so the gas escapes, 10% a year is deemed acceptable. So if never topped up it will be low. Then as it was getting low on pressure, the next bit tends to happen slowly over 2 years .... One major part "a condenser" made deliberately out of baofoil budget brand tin foil rot, sits out front getting pebble dashed with stones, road filth, nasty cleaning chemicals and road salt in the winter. And these self destruct in 7 to 9 years - the first sign is weeping dirt stains around the edges, with oily, dusty, dark areas.

Mercedes charge $1000 for the part but you can buy them direct from the supplier for $200 https://catalogue.nissens.com/FrontPage

RichDMB

BOTUS, thanks for the info. With the condenser being up front, it looks like it is an easy swap. Is it possible to disconnect the old one, then install the new one and simply add R134? If yes, do you just get the R134 gas or the R134 with PAG oil? I once heard the any time the AC system is opened, you should replace the dryer. Is that true?

RichDMB

BOTUS et al,

Nissens has two different part numbers for a condenser for my year model, 2008 S5504MATIC, 940137 and 94858. My car has a build date of 10/07, but it is not clear on the Nissen website which part is needed and they are different sizes and patterns. Which one is it?

BOTUS

its not easy half the car has to come off... or you chop off a bolt to get it out and leave it off and do the job in a few hours...

I re read all your symptoms and whilst quite confident it will need a condenser - nearly ALL cars over 10 years need one... (or if its made by Porsche then needs it in 3 years and 1 day of build alongside both intercoolers), I don't see this fits all the symptoms you state.
Often when low on gas the system cuts out totally its the other way around to yours... it starts out turned off low and gas and as things warm up sometime it perks in to life after 15 minutes. Are you sure its not just a cold car and as the air pulls high outdoor ambient temps you know its not working? Otherwise i wonder if something else is telling it to cut out - but we don't see that issue much here

as for part numbers check dimensions one is much taller - you can measure your and see the difference

RichDMB

OK, I feel happy as heck and a little bit stupid. My AC is blasting nice cold air and keeping me cool, meaning I don't have to drop big bucks (at least now) on a Mercedes AC system.

All I had to do was hit the two AUTO buttons and the MAXCOOL message was displayed in the COMAND screen, the that sweet cold air came a'blasting! Using just one AUTO button has it working as well.

Arrie

Based on what you say you do not need to replace condenser as your system works at times. When reading your posts I was going to suggest to you to put the AC system on MAX COOL, i.e. to the coldest setting but you already did that.

If the system gives you cold air in MAX COOL setting it has charge and works but it indicates cabin inside temperature reading error. When in AUTO and not in MAX COOL the system controls cabin temperature to the setpoint but when the temperature sensor reads temperature way colder than it really is then the system stops blowing cold air. MAX COOL does not care about the temperature setting and gives MAX COOLING at all times, that is why you get cold air from your system.

I have this intermittent problem in my car and I have read temperature from the sensor and it has shown way cooler values than what temperature really is. I have not replaced the sensor yet as most of the time it works fine. I think it could be just an issue with connections in wire harness but I probably don't get to it before it completely fails. MAX COOL always works.

Temperature sensor is that red dot in the dash left side of the START button. You access it from below.

Senecat

Pull codes.

Arrie

If it is the same problem as mine there is no code. Sensor works but just reads wrong. System thinks all is good but comparing the actual temperature measured with some other gauge or just how it feels to the sensor reading by scanner tells what the problem is.

BOTUS

there is actually shed loads of madness that goes on in the control unit - I had read there are nine interior sensors - but rear AC cars do get lots more like auto recirc for traffic fumes etc. so maybe the 9 sensors come with that option?). There are even customisable options for multiple preferences that can be coded to an individual car

I reset mine to standard using a reset procedure I got at with the snap on tool, and ended up seemingly worse - but I suspect its the duo valve near the brake master cycl. But asking a big indy the other day they agree the Merc duo vales are awful "but have never done one on a w221"

Note full heat at the back (for car with rear AC is often the expensive valve under the wheel cover of on my RHD car - the drivers right front wheel), the $50 duo valve under the bonnet reduces and or stop heat anywhere.