[W126 Coupe] A/C Not cooling

Gerry Van Zandt gerryvz at me.com
Sun Aug 14 13:39:09 EDT 2011


If your A/C system was just the stock R12 system that was converted over to R-134a, it will NEVER cool more than about 60% as well as the R12 system did UNLESS (as Dick explained) key components of the system are changed over to those that are optimized to work with R-134a. R-134a requires a different set of parameters to work at its best and this is just not possible with a stock R12 system that has been emptied, new fittings installed, and filled with R-134a and compatible oil.

Dick did it right as he explained it, and thus is getting excellent results. On the other hand, I had my system on my 1989 560SEC converted to 134a about 2001. When I lived in Portland Oregon, where the temps rarely get above 85F in the summer, the 134a system (with its reduced capacity) worked just fine as long as the refrigerant level was up to the correct level. However, since moving to Houston 3 years ago, I've found that my 134a system is pretty miserable in the summer heat.

My system is in tip-top condition (no major leaks, and all key components in good operating condition, though they are the stock R12 components) and it only works decently when the car is moving in traffic. Over long interstate trips (say from driving from Houston to Dallas) at high speeds it works quite well. Never ice cold but will get the car down to a very comfortable/cool temperature.

I find the same thing as well -- below temps of about 80-85F outside, the converted system actually works quite well.

However in stop and go traffic, it's miserable and pretty much just blows warm air after a minute or so of being stopped. I'm actually preparing to change my system BACK to R12 this winter -- my home A/C guy just sold me a left-over tank of about 15 pounds of R12 (for $50) that he's had sitting around for the past 15 years and not using. I'll have my indy shop test my system for leaks, replace any components that need it, and have the R-134a removed & then the system cleaned out several times with solvent, R-134a fittings removed, and having new oil and R12 introduced back into the system. Not an easy retrofit, but I can't handle another summer of only mediocre cooling. My 1987 560SL (still on R12) is excellent in all conditions.

The bottom line is that you'll never get good efficiency from an R-134a conversion (from an R12 system) unless key components are replaced. Systems designed specfically for R-134a (such as that on my 1994 E500 W124) work very very well (though still not quite as good as an R12 system, IMHO). It's 96F outside and I just got home from downtown Houston (30 miles away) and was nice and chilly in my E500 all the way up I-45.

It's a serious consideration for those with R12 systems that have been converted to R-134a, to change them back now that the price of R12 has come WAY WAY down and the price of R-134a has gone up. The difference in efficiency is truly worth making it worth considering.

My two cents.

Cheers,
Gerry




On Aug 14, 2011, at 11:15 AM, mbcoupes-request at mbcoupes.com wrote:


> Message: 6

> Date: Sun, 14 Aug 2011 08:22:36 +0400

> From: Yousef <usef4188 at gmail.com>

> Subject: Re: [W126 Coupe] A/C Not cooling

> To: Mercedes Coupes Mailing Lists <mbcoupes at mbcoupes.com>

> Message-ID: <A5B63E26-49EA-408A-9634-0A612B4719A2 at gmail.com>

> Content-Type: text/plain; charset="us-ascii"

>

> Yup runnin at 134a..

>

> Sent from my iPhone

>

> On Aug 14, 2011, at 2:00 AM, Jonathan Hodgman <jhodgman at gmail.com> wrote:

>

>> ya'll running R134a??

>


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