My 1990 300d got R134 conversion. A week later, I heard 'hissing' from center vent... next 2 days air became hot again. Local hack who did not warn about higher 134 pressure may have forgotten other essential. I need smart guidance on best fix.

Apparently. The evaporator can be accessed/replaced from outside of firewall. Is this a viable option? http://www.2phast.com/190E/ac.htm

Am ready to replace all the parts behind dash myself. So I would greatly appreciate you help:

1. When should I test for leak? Need AC specialist or can I test myself?
2. Can I get evaporator without removing dash?
3. Any R&R pix/instructions for the DIYer?
4. Need testing/special tools or an AC guy while dash is off?
5. What brand/numbers of all parts to be replaced in dash + under hood?
6. Dark soft foam blowing out center vents. What do I need to replace?
7. Should I flush system & reload R12 or run R134 for next 10 years?
8. What other parts should I change in addition to the pressure switch and dryer?
9. What sequence – before/after flush/reload?
10. How can I find best [non dealer] AC shop in South FL.


Thanks for your advice.

profitsharing

There are plenty of posts on this, suggest you try a Search. As you will see, if your evaporator is TU, you are faced with one of the most difficult and expensive jobs on the 124. So you at least need to get someone to verify the location of the leak.

And if it is the evaporator, I can't imagine spending that much effort and not going back to R12, especially in your area.

Good luck.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I'll take a stab at answering:

1. Before the guy performs the R-134a conversion.
2. No, no way, uh-uh. The website you reference is for a 201 chassis car, yours is a 124. Big difference.
3. Not enough available on the web, you must have the factory shop manual.
4. Basic hand tools are sufficient for replacement, special a/c tools are necessary for charging with refrigerant.
5. I don't have those memorized, lots of good discussion on it available here using the search function.
6. It's coming off the various doors that open & close to direct the air where it needs to go. Nothing to replace really, just vacuum the remainder off while you have it apart.
7. R-12.
8. Anything that leaks. New expansion valve is usually warranted when taking apart the system.
9. Huh?
10. Beats me, I'm in Texas.

Seriously, when did you hear the hissing sound from the vents? All the time, only when driving, only when accelerating when driving? When a bit low on refrigerant these things hiss. I suspect you have a good size leak - it may or may not be in the evaporator. Best to invest some time and effort in locating the leak before diving into the dash.

- JimY

Thanks jcyuhn

The leak became audible on day 4 post retrofit/charge. The hissing was noticable when the AC was turned on and at low fan speed. As soon as I stopped the AC, so did the hissing. THe last 2 days of uss [day 4 and 5] the cooling ability became noticably inefficient spewing warmer air by the minute.

BTW, # 9 refers to the proper sequence of part installation in relation to actual R12 refil. For example, I presume I would not replace the dryer until the system has been completely flushed and is ready to be refilled at the AC shop.

Also wonder what parts need to be changed. The mec who put in the R143 told me he did not replace any parts. Is it possible that he use the existing connectors to load the refrigerant?

Thx for your help.

RM

Try to ascertain exactly where the leak is. I am going to speculate that the higher pressures of the 134 system propagated a leak that was waiting to happen.

__________________
Jim

But why would the evaporator only leak when the AC was turned on? The pressure in the evaporator is actually lower when the AC is operating.

Seems like if was leaking enough to hear, it would have leaked down in a lot less than two or three days.

__________________
2012 E350
2006 Callaway SC560

I'm sorry to hear of your A/C troubles....Especially in S. Fla.

You asked for a place that does A/C work in S. Fla. East or West coast?

What I would like to suggest you look into, is how the compressor fared in all this. Was the right oil used?

IF.....the whole kit-n-kaboodle is near ruined, and you are going to have stuff apart, might it not be worth it to install a whole new system that was designed for 134? (ie: parts from a later model year) I guess it would depend on how much money you want to invest, and how much longer you plan on keeping the car.

Just a thought or two...

-Larry

__________________
It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

Are we all sure its a R134 leak and not a vacuum leak???

__________________
Hanno
'79 6.9 Sold (after 27 years)
'83 280SL, 5 spd.
'94 E320 Sdn. 5 spd conversion
'02 E320 Sdn.(on loan to mom!)
'87 300E (5 spd. conversion) Sold
'05 E500 Wagon

On the 124 chassis, the a/c will make a hissing sound when it's low on refrigerant. It's actually pretty typical behavior for an expansion valve system, just seems to be more noticable on the 124 than most other cars.

He may or may not have a leak in the evaporator - nobody knows. First order of business is to identify and repair the leak(s).

- JimY

So what is the best way and steps - just so that I know how good or poor the AC guy is. Should he be testing current pressure in the system before or using a gas sensor in the vents before injecting dye?

Your A/C guy should be able to identify where the leak is coming from and he should be able to fix it. On the other hand I would think he would have tested the system when he performed the conversion...

The "hissing" from the front vents is totally normal - what you are hearing is the expansion of the refrigerant in the evaporator. You should hear the hissing when the compressor is enganged - and it will be most noticable at low fan speeds combined with low car speeds.

Your car (especially in Florida) is a bad candidate for R134 conversion - go back to R12.

I would not embark on an evaporator replacement without verifying the evaportor is leaking.

Thx for the valuable insight. I will have the refrigerant level checked. But what is the best way for an AC guy to do this? I want to learn enough about the right way so that I can keep from getting any deeper. And how do I back up/out of the R134?

Does the system need to be flushed before R12 reload? What is the process? Any solvent? What oil type goes back in? WHat part/s do I need to change & at what stage of retre-retroconversion back to R12? Like do I need to change the dryer - when?