Our 123/126 A/C systems take too long to cool down, why
 

Hi guys,

Looking to start a discussion about the length of time it takes the A/C to start blowing cold cold cold....blah.......

From an engineering standpoint, why does the wife's '02 Explorer start blowing cold almost immediately and both of my 123's have taken some street time to start blowing cold (cold like you know you're on the right track)? It can't be the 134 vs R12 debate. The Ford runs R134....so I'm throwing it out there. And just for the record, my 123 will blow 35F on Freeze 12, just takes awhile to get there. Yeah I know the system is 25yo and the evaporator is probably dirty. What else?

i think these car's A/C systems have not been their strong point. Flame on kids:

The AC system was not your car's strong point.

The W210 factory 134a system starts cooling nearly instantly.

It's not the refrigerant necessarily, but simply the systems themselves. The Ford system was designed to be large enough to do the job plus a little extra. It's simply a higher capacity cooling apparatus.

The apparatus they put on the Mercedes, for whatever reason, is simply trying to do a job bigger than it's capable of, due to being designed to a less stringent requirement than that which we'd prefer it to be fulfilling.

I.e.
 

Ask any German driver if Frostbite type A/C is/was ever at the top of His/Her list
of most important attributes for an automobile.

Wasn't until somebody dragged somebody else (maybe Werner Von Braun was the dragee) out to Death valley at Summers height that word filtered back to
Deutschland that a refrigeration system would be appropriate in a luxury Auto.

RANT: You can,with a little effort,have your MB deliver Frosty Air Instantly...
1.Parallel Flow Condenser (As Large As YOU can STUFF in front of the Radiator).
2.NEW (NOT REMAN) High capacity Compressor.
3.Clean,Clean,Clean:Evaporator,Condenser ,RADIATOR,System Hoses,Etc.
4.Nylog for the New O-Rings.
5.NEW SEALED Receiver/Dryer.
6.Vacuum Overnight.'Holds vacuum? Then:
7.Pressure test with Nitrogen. O.K.? Then:
8.Re-Vacuum after Nitrogen is out.
9.Fill with the proper amount of R-12 and Lubricant.
10. Make sure you have "Long Johns (or Janes)" on.

I've always found my AC to be adequate.

I can start my F150 out in the driveway, leave it sitting there, come back in 5-10 minutes and the cab is freezing. {with temps in 90's or 100s}
Drive the Mercedes home, start with the interior cold, leave it sitting in the driveway and in 5 minutes it's up over 60 degrees. That is all of them with each type of refrigerant.
Condenser and evap are simply inadequate......

Hmmm. So then along the lines of Compressignite's post above it should be possible to retrofit almost any Mercedes from a Ponton on down with a custom A/C system that really will live up to the requirements of life in oh, say, Phoenix AZ for example.

- Peter.

Of course it is possible. That doesn't mean that it will be inexpensive.

Exactly. I have always found mine woefully inadequate but I have too many other places my money needs to stretch to.

The window tint on the back half of the car helped. The dark Orient Red paint in the summer doesn't help.

The AC on mine is great when moving. When stopped the temp creeps up to 60*F on hot days. No, it's not the rad fan(s), both electric ones work and the belt fan is new.

The system in my 99.5 TDI (which got a new $900 compressor in 2005) blows only slightly colder. The big difference is at idle. When underway there is almost no difference. The Benz does seem to cool the interior quicker. Perhaps because the dash is 1/2 the size?

-Jason

NEVER! I repeat NEVER test a system with vacuum... test with nitrogen FIRST!!!!!
if you test with vacuum, and it does not hold you have just ruined your drier!
look. think learn!
testing with vacuum is stupid stupid stupid.
it's only at most 14.7 psi differential from atmospheric pressure.
a HUGE leak will not show up with vacuum on a crappy charging manifold.
IF IF IF IF IF IF IF you have a DIGITAL micron gauge, AND AND AND you have experience with charging rates and vacuum rates of drop, you can get a feel for a tight system, BUT nitrogen is WAAAAAAAAAAY safer and easier to test for a leak.
PLEASE get it through your heads. DO NOT TEST FOR LEAKS WITH VACUUM!@!!!!!!

Anyone want to develop a 2 to 3 minute timed electrical relay that would automatically turn the aux fan on when the A/C is turned on? Kinda of like jump starting the A/C cooling process.

Think this would help?

I don't think it would help. Instead, insure that your refrigerant pressure and temperature sensors are working, and start the fan when appropriate.

Huh? The electrical fan in front of the radiator starts on its own when the temperature switch is triggered by the heat sensor in the receiver/dryer. You can't turn it on manually. My idea would be to design a circuit that would starting the condensor fan cooling process immediately but temporarily to get the condensor cooling faster.

That is my point.

If the refrigerant is not hotter than the ambient air, no amount of airflow will cool it. The hotter the refrigerant, the more efficient the transfer of heat to the air through the condenser.

If you want the fan to come on earlier, get a switch that engages the fan at a lower refrigerant temperature. There really isn't a reason to engage the electric fan if the refrigerant temperature is not hot and not under high pressure, unless you just want to waste energy and wear out your fan a lot quicker.

What I mean to say here, is that if the refrigerant is not hot yet is still a liquid, additional airflow will not help very much.

However, when you first start the system and the refrigerant is not even yet being introduced into the evaporator as a liquid, adding more airflow will not help AT ALL.

True, but the pressure and temperature will build in a few seconds, not minutes.

Hydrocarbon refrigerants have worked the best for me to improve on R-12. Better for the environment than R134A too.

It would be best if the system were designed for HCs, but they do seem to work well in practice. From what I read, the system won't get as cold at idle as with R12, but people seem to be happy with the results.

I'm more worried about R744 (CO2) as a refrigerant to be adopted by car manufacturers and its inherent dangers due to extremely high pressures. HCs have shown enough promise that I would rather the manufacturers go that route. A properly-designed HC system would chill you out of the car at all speeds.