I need AC advice!

[Sparks]

I just bought a new compressor for my daughter's 86 300E from PartsShop(thanks Phil for everything)per my mechanics recommendation and after he installed it, the same problem is continuing.

He had converted the system to r134 due to a leak in the schrader valve and replaced the dryer and expansion valve. The system would blow cool but not cold and the high side pressure was fine but the low side pressure stayed too high and the needle jumped a little. He diagnosed the compressor as having bad reed valves, hence the replacement. This mechanic was a Mercedes dealers head tech for 12 years and has come highly recommended but he can't quite figure out what's wrong. He has checked the condensor and he says it flushes fine so he doesn't think that is the restriction.

Any thoughts? I don't want to keep replacing parts when their not the problem. Also, the compressor on the car was rebuilt in Dec 99 and is in great shape, if anyone needs one.

Thanks for any help,

[jeffsr]

What are you getting for a center outlet temp? What are the pressures now? Is the compressor cycling? Does the low pressure line get frosty? R134a retro fits do not perform as well as R12 systems due to the compressor piston displacement and the size of the evaporator. Was the new compressor designed for R134a or R12? How much of an oil charge got put in and how much of the old oil got removed. Excessive oil can decrease overall efficiency of a converted system.

[stevebfl]

Jeff got a good idea about the oil. I have seen the problem a number of times and the conclusion I have come up with is that the evaporators on 300Es have multiple passages through them. I believe that they are next to impossible to flush. We use dry Nitrogen set to 150psi to propel the solvent. We only flush the evap with highly volitile flush. The oily flushes may clean well but the easiest passage clears first and reduces the ability to push fluid in the lower passages.

I believe the combination of flush and oil causes these problems.

[Richard Wooldridge]

Hi there,
Here's another thought for you to consider... it doesn't take as much R134 as it does R12 to fill the system, and high low side pressure is a classic indication of an overcharge. It actually only takes around 2/3 the charge in an R134 system by weight. If your mechanic is trying to put the same amount of R134 by weight in the system as was called for in R12, it's overcharged. I recently converted my system - it's a hybrid, having a GM compressor that ran R134 to begin with and the Mercedes 300D A/C system, but it works fine. It only took 2 cans of R134 to fill the system. By the way, if the original compressor had bad valves, it would show up as low high side pressure...
Richard Wooldridge
'82 300D/4.3L V6
'74 280C
'77 XJ6L
'77 280Z

[be459]

I agree with Richard but I assume that you tech know about the 2/3 charging rule. If some air got into the system while he was working on it, you possibly see the kind of gauge readings as you stated.

David

[Edited by be459 on 07-20-2001 at 04:31 AM]

I finally got cold air in my '87 300D after a r134 conversion. After replacing the drier, expansion valve, rebuilding the compressor, replacing all the seals the sysyem still wasn't cold. The pressures were fine, aux fan worked and cycled properly. The fix in this case was to replace the serpentine belt. With a worn out belt, the compressor wasn't turning properly, thus low cooling from the a/c system. We replaced the shock and pulley while we were at it, now the car runs quietly and cools properly.
This might not be your solution, but it was something we overlooked that made the difference.

Hope you get it worked out

Steve

Brothers of The Benz, All
Every year we all have the same problems.
There are those of us who had problems last year and corrected them; and now we are here to aided those who are where we were a year ago.
The early W124 Automatic Climate Control Air Conditioner is at it's time in life where the major components are in need of replacing.
The problem is made worse buy converting refrigirants.
The compressors have over 150,000 miles, the blower motor is at it's life end, the x-valve is lazy not to mention lines and hoses.
We want our technicans to flush the compressor and evaporator coil of old type oil. Have you ever seen the evaporator coil?
It's configuration is such that flushing is almost an impossibly task unless you remove it from it's housing.
If you have disassembled to this level you should replace everything inside the housing.
Too high head pressure or too low suction pressure.
Condensor full of bugs?
I bite the bullet and had my A/C completely rebuilt.
Both the high and low sides. Compressor/clutch with it's electronics, drier/reciever, x-valve, evaporator coil, all the vac-elements, resealed the evaporator/heater housing and a complete blower motor fan assembly, and convertig to R134A.
It doesn't cool as well as R12, but with the thermostat at 22C, the fan speed slows and when it isn't extremely hot here in Houston, the clutch cycles.
I probably spent more than my 1987 300E is worth; but having bought it new and maintained it as well as can be expected and after 14 years of faithful service she deserved it.
This will be my last car for at age 66 years it is more than I need.
You are right, Prince Phillip of Fastlane is super.
Happy Trails Beep Beep from The Spiderman in Houston!!!

[Edited by dlswnfrd on 07-21-2001 at 04:56 PM]

[Sparks]

I talked to my mechanic and I relayed the advice given, which He was a little miffed about, since he informed me that he is a 16 year certified Mercedes mechanic and new what to do!

Also, I did just replace the serpentine belt and tensioner last month, so that's not part of the problem. (thanks FastLane)

Anyway, he did do the high pressure solvent flush, with no better results. He is taking off the condensor to visually inspect it as he thinks this might be the problem. I hope it is!

I will let you all know the prognosis of the patient. One question though, how hard would it be for myself (a fairly good mechanic with tools) to take the dash apart and install a new evaporator and whatever else you replace at the same time.

Thanks,

[J.HIDALGO]

Sparks,
do a search on the subject. I am a DIY and I did it WITH the MB manuals. If you have the time (it took me a week) you are not afraid of HARD work, just do it! You will save BIG $$$. Make sure you have all the parts BEFORE you start. Oh, get a copper core evaporator.
Good luck either way!

[bill17]

This following isn't really technical but I hope the information helps.

While investigating blower motor noise, since the glove box and trim panels were removed, I took a look at the A/C air intake, as I was annoyed that outside air/fumes entered the car regardless if A/C was on or off. And by accident (didn't have a manual at this time) I found that the main air flap which controls the air intake weren't working due to bad switch-over valves, it had stuck open so there were no "recirculation" mode, which in turn resulted in reduced cooling. Upon replacing the valves the system did blow colder than before, as air is recirculated as required, thus had no need to cool the hotter air from outside all the time.

[Sparks]

Thanks everyone for the advice. My mechanic finally got frustrated enough to pull the condensor. He found it was crushed in from the accident the previous owner had. Over 1/2 of it was damaged enough to restrict the flow, causing the high low side pressure and poor cooling (we hope).

I ordered a new condensor from Phil last night and will have it here today and install tomorrow. I will let you know how it works out.

We put my old compressor back on since it was only rebuilt jan 2000, so I have a brand new compressor I got from Phil for sale, if anyone needs one.

Thanks again,

[samiam4]

Sparks,

As a general note to future ppl: "He had converted the system to r134 due to a leak in the schrader valve and replaced the dryer and expansion valve. "

He does not have to evacuate the system to do this repair!!! He can simply buy the $35 tool which will allow replacement. Seems auto guys don't know about these near as much as home HVAC service ppl.

Glad you found the restriction!

Michael

[be459]

I do not know much about home HAVC but for auto A/C, the only time I do not evacuate the system is when I am sure there is 100% freon in the system (such as after discharging a full functioning system). It is always a good idea to evacuate the system for at least 30 minutes (for me, usually one hour) before charging, just to be sure all the air and moisture are out.

David