A/C ineffective above 90 degrees outside - Page 5 - PeachParts Mercedes-Benz Forum

Brian Carlton · #61 08-21-2011, 10:35 AM

Quote:

Originally Posted by jbach36

Brian, I'm betting you're are a better mechanic than me, so I will defer to you. If you think MB ac units are just as good as any other car, I won't argue with you. However, from my point of view as a driver (not a mechanic) of 2 MB's, both W124's, I have found they cost me a lot of money on the a/c's, with multiple repairs (my current one I'm posting about on this thread, a 1991 300d with 167k on it), I've had repaired 4x in 4 years.

I've replaced the blower fan and regulator cable I think it's called that goes to the fan, then a MB specialist mechanic replaced a (?) drier or something once. I've had more freon added last year, then more this year, so we now know there's a leak. In all cases except this last recharge now just 3 or 4 days ago, the a/c has never been "cold". It'd been adequate at best, but no more. The other day, as I posted, it is blowing now at a very nice 40 degrees, and feels great. That's the coldest that car has ever blown, in the 4 years I've owned it.

On my 1988 300 CE that I had 14 years ago, ditto with that. It never cooled well. I took it to a MB specialist at the time, who "fixed" it for $500 (I'm assuming now he added a bit of freon for $500), and it didn't blow cold. I took it back to him 2 weeks later, and he made it like he was doing me a favor to work on it again. When I got it back, it blew a bit cold, but very marginal.

Also on both cars, I get the fog line on my windshield due to the pods not closing tight, so on a nice dry summer night, I'm the only one with my windshield wipers on. I've also seen many MB's here in Atlanta, and online, with tinted windows, which to me, is another way of saying their a/c's probably don't blow cold, and ones I've seen advertised, often say, "a/c doesn't blow cold, it probably needs a recharge".

But if you think MB's don't have more problems than other cars, I will believe you. My view is just from a driver's point of view and casual observations of what I've seen (ie, I haven't kept formal track of how many work, and how many don't). I'm also under the impression that BMW's did not have very good a/c's, either. From all the problems I've had on my 2 MB's a/c's, and probably $1,200 later, it seems to me their a/c systems leave a lot to be desired.

If I could wave a magic wand, one thing I wish MB had on these cars, is a simple low/med/high setting, and a quieter fan! Low is too low, it hardly puts anything out at all, so I nearly HAVE to switch to the annoyingly-loud auto or high settings ("auto" is typically high or low, the variable 'medium' setting it puts out temporarily doesn't stay around very long). I think on Honda's or Toyota's I've had of the same years, low is quiet and puts out a fair amount of air, and even a notch or 2 up on the fan is still reasonably quiet.

Firstly, I do not ask you to "believe" me or anyone else. Beliefs are for religious folks, not engineers.

Secondly, you've made mention of the various repairs that have been necessary to obtain the level of cooling that you desire. That's really not part of the discussion as any 20 year old vehicle is going to need a/c service, some of it quite costly. Check out 20 year old Ford and GM vehicles. You'd be hard pressed to find a functional a/c system that has not had any money invested.

You additionally make the conclusion that the system doesn't cool well based upon the obvious inability of a "mechanic". Most have no real knowledge of these systems and have virtually no ability to repair them properly.

I asked you to provide a definition of "good cooling" and you have failed to do so with any data. This request is not made without reason as the expectations of the driver weigh greatly on the definition in most cases. Personally, I try to eliminate the driver from the equation and simply use the scientific data presented to make a judgment. Since you have provided nothing, I will give you my analysis of the SD and the data presented and my conclusions:

System refrigerant: R134A

System charge: 100% at beginning of season.

Ambient: 85F with noon sun. Cloudless sky.

Interior temperature on start: 120F.

Vent temperature at six minutes after start (engine speed at 1500-2000): 60F.

Vent temperature at 20 minutes after start: 45F.

Cabin temperature achieves setpoint (20C): 20 minutes after start

When the cabin reaches the setpoint, the blower speed properly drops off to the third or fourth (cannot be sure).

At this point, the vent temp drops further to approx. 42F. At that point, the compressor drops out due to the ETS engagement and the vent temp nearly instantly climbs back to 50F. The compressor reengages.

Conclusion: The performance of this system is considered "good" by me at this ambient and with this refrigerant.

But, realize that it has a refrigerant that is not designed for the vehicle and won't cool as well as the proper refrigerant. If I lived in 100F. ambients, I would use the proper refrigerant and, from the comments of others, I could achieve about the same performance as noted above at the higher ambient.

My observations of newer vehicles are quite the opposite of yours. The 134 refrigerant vent temperatures are not any better than the SD and they use very high airflow achieve their cooling capabilities. They may achieve the high airflow with a larger or more efficient blower that makes less noise............

Take the analysis of the SD and see if you can do the same with one of your vehicles. You may find, simply, that it is not repaired to the necessary standard. This does not allow you to make the conclusion that the system doesn't "cool well" by design. It simply doesn't cool well in your vehicle.

vstech · #62 08-21-2011, 10:51 AM

Well said Brian.

ALL of the vehicles I drive perform as Brian describes... and I'm in the 100°F summer High humidity climate, and NONE of my vehicles have tint on them.
however, I am a Refrigeration expert, and I have all the tools and chemicals to maintain my fleet.
my plans to tint the vehicles are for aesthetics, and vehicle longevity as well as protection of the contents. (I'll take the lighter load on the a/c system that it provides as a more rapid cooling improvement!)

jbach36 · #63 08-22-2011, 06:16 PM

Brian, you said, "Firstly, I do not ask you to "believe" me or anyone else. Beliefs are for religious folks, not engineers".

No, no, no.

Believing in someone is what we all do, when someone else knows more about a particular topic.

I'm not a mechanic, so for me to come to the same conclusion you came to if you are a professional mechanic (I'm assuming you are, or at least a very serious hobbyist, since you know a lot of technical stuff), would take me 2 years. As one person said, "You can't know everything there is to know. There's not enough time, so you have to hire others who do know".

Sure, the mechanics I had in the past might not have known what they were doing (they should have if they took my money, and so much of it), but just looking at the number of threads posted about a/c problems, and experiencing them myself on my cars (my 1988 was only 9 years old at the time I had it), and seeing many other MB's driving around on scorching hot and humid days with their windows down (I doubt they wanted to feel the fresh breeze through their hair as they sweated), and others with windows tinted, all lead me to believe MB did not put a good a/c system in the cars. Not to mention the noisy fan!! Low puts out like, nothing. So you have to go to the auto or high, and can't even talk to the person next to you. I wish they would have put a simple "medium" setting on it, and called it a day.

All that said, if you are a mechanic, have worked on many other cars and say MB doesn't have more problems than any other cars, I'm not going to go out and do a survey, I'll simply.... believe you.

As to mine, now that my (good) mechanic added more freon plus the dye to spot the leak, it's blowing colder than it ever has, putting out 40 degrees now, and I'm quite happy with that on 94 degree days.

Brian Carlton · #64 08-22-2011, 10:31 PM

Quote:

Originally Posted by jbach36

As to mine, now that my (good) mechanic added more freon plus the dye to spot the leak, it's blowing colder than it ever has, putting out 40 degrees now, and I'm quite happy with that on 94 degree days.

I'm hardly a mechanic...........just been a backyard wrench on these things for 10 years or so.

Apparently, your opinion of the system might now be altered towards the positive side now that the system is functioning as designed.

As I mentioned, the problem was with your mechanic...........not the system design.

You'll now find that the high blower speed will be utilized only to cool the vehicle down upon initial start...........once it achieves the cabin temperature, it will reduce to a more tolerable level. Again, your issue with high blower speed..........incessantly..........was due to excessive vent temperatures. The system was trying to compensate as best as it could.

Doktor Bert · #65 08-22-2011, 10:59 PM

My wife uses the 1978 300SD for her Mary Kay business because the A/C gets colder and, more importantly, gets colder faster than her 2008 Dodge Magnum.

I can't give you any scientifica data to back up her claims, I just make sure the car is ready for her to use....Robert

Doktor Bert · #66 08-22-2011, 11:00 PM

Quote:

Originally Posted by Brian Carlton

I'm hardly a mechanic...........just been a backyard wrench on these things for 10 years or so.

Apparently, your opinion of the system might now be altered towards the positive side now that the system is functioning as designed.

As I mentioned, the problem was with your mechanic...........not the system design.

You'll now find that the high blower speed will be utilized only to cool the vehicle down upon initial start...........once it achieves the cabin temperature, it will reduce to a more tolerable level. Again, your issue with high blower speed..........incessantly..........was due to excessive vent temperatures. The system was trying to compensate as best as it could.

That's exactly right....Robert

jbach36 · #67 08-22-2011, 11:35 PM

Brian, I always thought you were a mechanic, because you know all this techno stuff; the settings, psi pressures, and on and on.

Do you work on any other cars, and if so, what is your take on how MB's are, compared to other cars, with regards to the a/c, and other aspects of the car as well? I see you have a BMW, how do you like that?

Also on my 2 cars, the a/c problems I had, were over probably 4 mechanics, 2 of them MB specialists, and 2 who were not. The guy I have currently, a general mechanic who mixed the R12 and 134 on purpose, has been the best guy. He doesn't know everything, but close to it, and if he doesn't know, he tells me. Very straight up guy. Just the other day when he added more 134, it must have been a better mix with the R12, because it was colder than what it was.

Even with the auto setting that CAN go to a mid setting but rarely did, I almost always have to have it on that setting, because the low is simply too low. I wish there was a way I could double the low speed. Even at double, it'd probably be adequate airflow and quieter than a "medium" setting.

engatwork · #68 08-23-2011, 07:15 AM

Robert - you should have posted that in the pretty girls thread

.

sjh · #69 08-23-2011, 11:11 AM

I very much agree Jim but wasn't sure if it would be mis-understood if I told him how attractive his wife is and how fortunate he is that she wants to make the effort to look nice for him.

x2

Doktor Bert · #70 08-24-2011, 06:01 PM

Quote:

Originally Posted by engatwork

Robert - you should have posted that in the pretty girls thread

.

Thanks, guys...

She is a wonderful person and very good to my sons....

Brian Carlton · #71 08-24-2011, 10:55 PM

Quote:

Originally Posted by jbach36

Brian, I always thought you were a mechanic, because you know all this techno stuff; the settings, psi pressures, and on and on.

Do you work on any other cars, and if so, what is your take on how MB's are, compared to other cars, with regards to the a/c, and other aspects of the car as well? I see you have a BMW, how do you like that?

Knowing "techno stuff" does not make one a mechanic. To obtain proficiency with wrenches requires one to be working daily in such a profession, something I do not have the time or the physical capabilities to achieve.

I try to tackle the issues on a vehicle by looking at it from an engineering standpoint and obtain the data necessary to make good decisions. Sometimes I succeed............sometimes I don't. Probably quite similar to the "professionals".

The BMW has a very different a/c system. It's extremely quiet and at maximum blower speed, the noise..........and the output...........is about the same as the middle setting on the M/B. It manages to do a decent job of cooling because the vent temp is 45F. and my ambients are not all that high. I do not believe it would do well in 100F ambients due to it's color (dark blue) and the relatively low airflow.

I happen to love driving the BMW because it's extremely quiet, handles far better than any of the M/B's and has about twice the power of the SDL. It's a big and very heavy vehicle and is not very well suited for driving in the city. It's also a primadonna when it comes to repairs. The general consensus, and I will concur, is that it will consume about $3K worth of parts and labor per year. This one might be a bit less because my yearly mileage is about 5K (it only goes on vacations and road trips). The parts are quite costly and they give out with relative frequency.

jbach36 · #72 08-25-2011, 01:57 AM

That's bad to hear that the BMW fails frequently. Germans usually build good stuff, but they had their bloopers, too. I think people hated the 2002 VW Jetta's. Windows would go down, but not back up, at around 30,000 miles, along with other issues.

Japanese cars have very few problems, but they are lighter cars, which is easier on a car overall.

I think earlier BMW's, the 1989 and prior era, had some serious cars, that were made very well from what I understand. The 740 is the heaviest, so it stands to reason it's more wear and tear on everything. Lighter cars have a smaller engine, but easier job overall. Plus, people tend to beat BMW's because they're so quick, and fast starts are very hard on a car. Maybe one reason why MB's last so long; they're not quick.

Brian Carlton · #73 08-25-2011, 09:09 AM

Quote:

Originally Posted by jbach36

I think earlier BMW's, the 1989 and prior era, had some serious cars, that were made very well from what I understand. The 740 is the heaviest, so it stands to reason it's more wear and tear on everything. Lighter cars have a smaller engine, but easier job overall. Plus, people tend to beat BMW's because they're so quick, and fast starts are very hard on a car. Maybe one reason why MB's last so long; they're not quick.

The weight is not a factor in the wear and tear. It has an engine that is more than sufficient for the task. In fact, BMW set it up so that it won't rev past 3300 rpm, although the redline on the tack is at 5000. Doesn't make any sense to me, but, apparently, it's a characteristic of the vehicle.

The vehicle has a slew of expensive items that will really dispose of money in a big way including the transmission and the digital dash display. It also has a very sensitive emissions system and if any one item is slightly off spec, the CEL comes on. At the present time, it's toying with the thought of replacing the left cat, but it isn't positive about that. Then, there is the issue of whether to go aftermarket on the CAT or buy the OE part. The price discrepancy is enormous (3X) but the risk of a failure to meet the computer's requirements is eliminated. It's an interesting vehicle.