Evaporator: To Replace or Not to Replace?
 

Last Fall I picked up a 1992 300D 2.5 Turbo with 137,000 miles for $5900. As far as I can tell, it's in perfect condition except that there's a hole in the evaporator. When I got it, it was a pound low on R134, with no evidence that the previous owner had ever serviced the AC. So, as a stop gap measure, I simply had the R134 recharged and recycled and, six months later, it's still blowing cold; I'm hoping to make it through a Texas summer.

The R134 service cost me about $125. Replacing the evaporator would cost me $2200.

My questions:

1. I'd sooner pay $125 for the recharge every year forever than spend $2200 to replace the evaporator. Is there any downside to this? Is there any risk of my harming something in the AC system by not replacing the evaporator? And is the hole likely to get larger?

2. I'm aware of the fact that the evaporators on this vintage MB have been problematic. If I replace it, is the new one likely to be just as problematic? Or did the manufacturers solve whatever problems plagued the originals?

FYI, I'm planning to keep the car for a LONG time (15-20 years).

Thanks so much for any advice anyone can offer.

David Sherwood

If you don't let it get real low you can recharge r134 yourself. Guages are cheap ($15) and a can of r134 is around $4..... and it's very simple. Obviously it's better to fix it but the cost is quite high.

It has been my experience that holes....evaporator, hoses. tires, rusted fenders, underwear, etc...ALWAYS get bigger...with the 134a I too, would just get a "can tap" and top it off...if you are only talking about once or twice a year. You might buy yourself enough time to find a better deal on an evaporator, or find a less expensive one that will fit.

To begin with, $125 to top off a 134 system is a rip off price.

Secondly, you have said nothing about a diagnosis that has proven that the evaporator is the source of the leak. There are zillions of other possible places that could leak.

Diagnose properly before making such a decision.

Have you diagnosed yet?

Good luck,

If you have a "small" leak somewhere (6 months and still working) I would top it off for 20 years before I spent over 2 grand. Besides, how do you know there is a hole in the evaporator? Many other things could happen, few if any can you predict.

Larry,

Re diagnosis, yes, a very reputable indie shop diagnosed it as a hole in the evaporator. They even used the phrase 'large hole," which surprises me since it's still blowing cold after a number of months.

Re the $135, that wasn't just to top off the R134, but to evacuate the system, leak detection service, etc.... My hope was that they would simply add the pound of R134, but they wouldn't.

if you had a "large hole" in your front tire, would you still be driving on it 6 months later? Even though the shop you used is reputable, are you dealing with the principal or a well meaning but inexperienced associate?

One of the things I seem to be getting conflicting advice on is whether simply to top off the R134 from time to time (easy, cheap, something I should be able to do myself) or to evacuate the system when I recharge (I guess to prevent moisture/dirt from entering the system).

by keeping close tabs on your system's operation, checking pressures fairly often and adding just a little bit (when you really need just a little bit) you can maximize the chances of being able to do it all yourself on the cheap for a long time. However, if you let it go until it works intermittently, a real leak on the low pressure side will be at a lower pressure still and can be the path that contaminants use to accelerate problems in the system. No guarantees, but then that's part of what DIY is about.

shertex,

Since the AC system is under positive pressure, no contaminents will get in as long as it is not allowed to go completely empty. There is a pressure switch that will not allow the compressor clutch to turn the compressor if the pressure is to low.

So as long as you keep enough refrigerant in the system so that it functions, you should be OK adding refergerant as needed.

If you replaced the evaporator yourself, it should only cost the price of the evaporator and new refrigerant.

P E H

As long as your system is blowing some cold and the compressor engages, you have positive pressure in the system and no chance of air/moisture/debris entering the system, hence, no need to evacuate, and you can simply top off the system as needed. Once the system has no pressure (the gage pressure is zero), then you have to treat your system as if it's contaminated.

And please don't use the 134 cans that contain stop-leak stuff. This will result in very expensive repairs later on.

PEH is right about the pressure keeping contaminants out, except when the system is operating with just enough pressure to make the switch and there is a leak in the flexible part of the SUCTION side of the system(like a hose), there is the possibility of creating a vacuum and bringing in moisture. Mke sure that pressure switch isn't bypassed though, people do all sorts of things

kestas, What kind of AC background do you have which would qualify you to contradict all the AC manuals I have ever seen ?

I suspect you are using " common wisdom" visualization... which does not conform to the physics of automobile Air conditioning systems.

Thus, Pete is correct. ( again )

We may be cutting hairs here about a large leak vs. a small leak. I just had a large leak with my pressure switch that sits on top of the receiver/dryer (for those of you reading this for educational purposes). After 4 days the pressure switch would not trigger the compressor, that is a large leak. If your system is OK after 4 months (with the more pressure sensative R134), I would consider that a small leak.

To R&R the evaporator in a 124 or 201 chassis is about 15 hours labor???? Any input here folks?? TX labor being less than CA labor, $2,200 sounds high. Now if that included replacing ALL the pods and other wear items while the dash was out maybe the price would seem more reasonable. If you want to keep the car that long what about replacing the heater core too while the dash is apart. AND does the dashboard have any cracks?

Sounds like you want to cherry it out.

The rest of you already beat me to the punch in regards to the issue of diagnosis.

The leak could also be where the hoses and expansion valve connect to the evaporator. You should be able to check for leaks in this area with out removing the evaporator.

P E H

Leathermang, I was interrupted while composing my post. It was composed AFTER shertex asked about conflicting advice and BEFORE Pete gave his advice. I'm sorry if it sounded like I contradicted Pete. I was only trying to help sort out shertex's confusion.

BTW, why did you choose to criticize MY post instead of PEH's, who essentially said the same thing as I did?

Kestas, don't sweat it. When you said "you can simply" in your post, every single hair on Greg's neck stood straight out. (I know, because my neck hairs do that too) However, I've noticed that A/C is a second religion near the equator, and that's why I've been haunting these posts to learn more myself. You and I can get by with opening the window for 11 months a year.:cool:

If it's still cold after six months, it's not a large leak.

Only problem with your proposed solution is the a/c system contains both refrigerant and oil. The oil lubricates the compressor. Both refrigerant and oil leak out of the system. When you run low on oil, the compressor will seize and fail. It's ugly.

As an alternative you could add oil each time the system is recharged. Only problem is you don't really know how much oil to add.

FWIW, a 30lb container of R134a can be had for ~$100. Another hundred or so for guages and such, and you could keep it topped up for a very long time for about $200 bucks. I actually did this for a few years with my 124 until I got around to changing the evap. In my case it was only going about three weeks between recharges; at that point the inconvenience starts to factor in and override the cost of replacing the evap.

- JimY

NEVER CONTRADICT PETE !!!!!!!!!
 

Kestas, To start with , here is your statement:

"As long as your system is blowing some cold and the compressor engages, you have positive pressure in the system and no chance of air/moisture/debris entering the system, hence, no need to evacuate, and you can simply top off the system as needed. Once the system has no pressure (the gage pressure is zero), then you have to treat your system as if it's contaminated."

Aside from the fact that it is wrong.. it was said with such confidence that I thought I would ask where you found such feelings.... It also shows you missed a couple of times in AC threads lately where this has been discussed... and at least once where I volunteered to take a picture of the statement in one of my AC manuals which clearly states that a leak is to be considered as having contaminated the system...

I hope and assume that you are more easily swayed with facts and argument than PEH, whom I have given up on affecting due to the basis of most of the things he says which I disagree with... because the differences come from his philosophy of frugalness ... which I consider "over the top"... he took me to task in an email in which he did not like the term I was using ( force) when air pressure is applied to a piston ... and he has hot buttons which include motor/engine,gas/fuel, etc... I still have not figured out what he was saying in that email about ' force'.... and I really tried...

but basically I came up the thread from the botttom... and did not see PEH's statement... just saw yours... LOL

I missed those threads. I know the suction side on a healthy system is above atmospheric. As you can realize, I thought the compressor cuts out before pressure drops to where the suction side goes to vacuum. Thanks for setting me straight.

Just trying to keep moisture and dirt out of everyones AC....

Leather,

If you still can't understand the difference in pressure and force, you need to take a course in basic physics.

P E H