Colder AC any ideas? - PeachParts Mercedes-Benz Forum

Hip001 · #1 07-24-2009, 02:37 PM

Hey guys thanks for your replies here.

I have a 1985 300d and a 1986 300sdl. I was wondering in general if there is a way to make the AC work better in both. Both have been converted to 134a and seem to work ok but here in Florida it gets HOT! both seem to blow consistantly close to 50 while getting close to 40 degrees on occation for very short periods of time. According to the mechanic the levels of 134a are fine.
Any ideas?

Thanks for your help!
Hip

brandlj · #2 07-24-2009, 02:55 PM

I feel your pain. I have a 86 300sdl and live in NE Louisiana where the heat and humidity can be brutal. I solved my AC problem by buying a 2007 BMW 530i for daily driving in the summer, and when fall comes I revert to the Benz.

Seriously though, converting our cars to R134A is what the problem is. My 85 380se still uses R12 and it has excellent airconditioning even without the 1986 factory update to the Recirculation switch. My 86 300sdl is light blue with a dark blue interior. I use sun shades on front and rear window when I park at work. I have cleaned the condenser and radiator coils. I have replaced both vacuum pods for the reirculation door. I have a good charge of R134A. I have connected both of the wires to my drier switch together, so my low speed aux electric fan runs all of the time. In city driving, I am doing good to get 48-50 degrees out of the center vents on a 95 degree day with 60 percent humidity. On the Interstate at 70 mph I will get 40-42 degrees out of the vents. Other than switching back to R12 I don't know what else we can do.
Some people have changed their condensers out to a parallel flow, but I have not.
I do plan on experimenting some more with a nice set of DUAL electric fans for in front of the radiator from a 1991 420SEL. I don't know if this will help or not.
Seriously on 95 degree days, I drive the BMW. It will blow ice cubes.

leathermang · #3 07-24-2009, 02:55 PM

The chances that you AC system has had its evaporator fins cleaned is slim and None..
That is where I would go for the cheapest best shot at really helping out your coolness.
Check in the archives for a thread by DMorrison in Dallas about cleaning his... and what he found when he looked at it... with it hidden away it just keeps getting overlooked decade after decade until finally you can have all the other stuff working well and still have that Achilles heal hurting your cooling.

nlines · #4 07-24-2009, 03:42 PM

The problem with R134 in your car is that the Condenser is not big enough for the R134 to work properly. I have read that you can buy modern cross flow condensers that will help.

Jeremy5848 · #5 07-24-2009, 07:15 PM

What would be involved (cost, complexity, etc.) in converting back to R-12?

#6 07-24-2009, 07:22 PM

I have reverse converted several cars and it's not that bad. You will need; flushing agent, oil, R12, o-rings and a filter/drier along with, of course basic a/c service equipment and compressed air.

Break all connections and put flushing agent in each component and blow out thoroughly. If you don't have a flush cannister you can use brake cleaner. Thoroughly flush all components with the solvent EXCEPT the compressor. Flush the compressor with oil. Once everything is flushed and THE FLUSHING AGENT THOROUGHLY BLOWN OUT, put everything back together putting in the new filter/drier last. When putting it together, distribute 8 oz. of oil in different components. Turn the compressor a couple of dozen turns by hand to make sure it's not liquid locked.

Make sure the filter drier does not go on until you are ready to evacuate as soon as it's cinched into place. At that point, evacuate and charge with R12 normally.

The 123 and especially the 124 MB's are some of the poorest candidates there are for conversion to 134. A reverse conversion would be a very good step.

Good luck

leathermang · #7 07-24-2009, 07:30 PM

Even if you wanted to convert to R12 at some point later...
cleaning the evaporator fins would be great for both situations.
and it does not involve breaking into the system.
and it might make enough difference to be able to hold off till better weather to work on it.. There are no downsides to having the evaporator fins clean.

daw_two · #8 07-24-2009, 08:53 PM

I've read and been told that the condensor size in the 300SDL is large enough; however the 300D is smaller and suffers when used with R134a.

Coda was R12 when I bought her and haven't done anything to her. My main compliant is in stop and go traffic. If I'm doing 55mph, the AC was good enough last year.....except when the ACC decided to have a mind of its own.

Also, check the outside air flap --- make sure it is closing ALL the way when in the RECIR position. You are using the "max cool air" position on your ACC, right?

As part of this year's work, I want my Aux Fan to come on at a cooler temperature. I might even mod it to come on when I'm in stop & go traffic on a hot Memphis day.

kingdoc1 · #9 07-24-2009, 09:00 PM

Converting your cars back to the proper refrigerant will solve your problems.

Your R12 systems were designed for R12, not R134A. R134A system components are sized differently, because the efficiency of the two refrigerants is not the same. R134A only performs well in a system designed for it, and even then, it still cannot match an R12 system.

I have yet to hear of anyone who has a properly functioning R12 system and is unhappy with it's performance, but you don't have to look very far to find many who have converted to R134A and are sorry they did.

I know this might not be what you wanted to hear, but its the truth.

#10 07-25-2009, 11:24 AM

For the most part KingDoc is right. For German cars everything he says is certainly right.

With many American cars made just a few years before the change to 134 (early nineties and some late eighties cars) they convert quite well if done reasonably and properly.

Gene Horr · #11 07-25-2009, 02:02 PM

Refits to 134a will work if your outside air never gets above the low 90's. For those that don't live in those sorts of frigid wastelands R-12 is the best and cheapest solution.

Assuming no existing problems you are looking at $400 - 500 for an honest shop. You'll probably need to track down your own R-12. It is readily available on ebay, craigslist, or even this web site every once in a while. The average price is a little under $30/lb shipped to you and you'll need a little under 3 lbs.

You'll need:

3 lbs. R-12
1 bottle mineral (NOT PAG) R-12 oil
Dryer
O-ring kit

and you might want to change out the pressure switches at the same time.

All of this is under $200 for the parts.

My local shop charged $150 to evactuate the system, test for leaks, and then to add oil and charge. If you budget $500 for the whole job you should be fine.

My daytime temperature right now hits 103 F on average with peaks at 107 F. The stock system works well in city driving up to about 100 F. At that point I've got to keep the fans on high to be comfortable. On the highway the system works better but as that is not in the concrete oven in the city the air temps are lower there and so I have not tested the system above 103F on the highway.

#12 07-25-2009, 03:13 PM

I just drove back from town (20 miles away) and it was 101. I was in an 88 model Corvette. These are said to have poor a/c systems. This car was one of the first that I ever converted to 134 and that was probably about 1995. I don't convert them any more. Anyway, this car is red and soaked lots of heat setting on the parking lot. By the time I was a couple of miles out of town I had 40 degree vent temp.

I am NOT now a proponent of converting an R12 to ANYTHING besides R12, but the later US cars, for the most part, convert very nicely. German cars are NOT good candidates for conversion. Germany is not known for lots of 101 degree Fahrenheit days.

Brian Carlton · #13 07-25-2009, 04:40 PM

I've recently made an observation on the '87 SDL that I'd like to have confirmed by others.

Firstly, this vehicle has no a/c at the present time, so, naturally, I prefer to use the fan on high speed to move some outside air through the vehicle. This works perfectly fine on the first start of the day while the engine is cold and hasn't reached temperature.

However, on subsequent starts, the temperature of the discharge air is estimated to be at least 15F. above ambient on starting.........gradually getting closer to ambient as the vehicle is driven for a distance.........but never quite making ambient temps.

My thought is that the heater core is flooded with hot coolant upon shutdown because the monovalve opens fully.

Is anyone aware of a check valve that prevents this behavior? For those using a/c, it must overcome the hot coolant in the heater core, thereby making a marginal system that much worse.

Anyone with some input or willing to confirm the above is welcome to chime in.

WD8CDH · #14 07-25-2009, 05:54 PM

The monovalve on one of my 123's leaks even when off. Due to health issues, I haven't been able to fix it yet but it really makes the AC worse.

Other than changing back to R12, converting to HC12 is a way to get better cooling than R134a. I have found HC12 to be very slightly better at cooling than R12. I have used it in about 6 cars.

snookwhaler · #15 07-25-2009, 06:09 PM

Quote:

Originally Posted by Hip001

Hey guys thanks for your replies here.

I have a 1985 300d and a 1986 300sdl. I was wondering in general if there is a way to make the AC work better in both. Both have been converted to 134a and seem to work ok but here in Florida it gets HOT! both seem to blow consistantly close to 50 while getting close to 40 degrees on occation for very short periods of time. According to the mechanic the levels of 134a are fine.
Any ideas?

Thanks for your help!
Hip

If your certain the charge is good, I would go with cleaning the evap.

Then go under the hood and insulate every pipe you can find that carries the cold stuff (low side).

After that go out to the front of the car, remove the aux. fan (or fans) and clean the Sh@t out of the condenser. With the amount of love bugs, dragon flies, gnats, mosquito's and butterflies... It is likely that you condenser is at least partially blocked. A little soap, water and a toothbrush works pretty good. Then blast it with water and re-install the fan (or fans).

Also, I found on mine that a bunch of the condenser fins were bent. So, I spent a good hour with a tiny screw driver bringing all the fins into the correct position. They make a special "comb" for this, but I did not feel like driving around trying to find one. It is not that difficult to fix them. Anything blocking air flow is reducing the efficiency.

I get 35 to 37 out the vents on mine with R12. Even on the 99 degree days. I imagine the 134 might be a little less, but not much. If you are getting 40 out the vents... My bet is that you probably won't be able to do much better.

Good Luck!!

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