Chris Carson

Well, I found instructions how to obtain temperature and pressure readings for my E320 by utilizing the A/C control panel. After checking and recording this data, as well as the trouble codes, I decided to clear the codes to see if they would return. As of now, the codes have not returned, but I still am having trouble diagnosing my problem(s). The below is the last data pulled from my system by component number:

1. 29
2. 35
3. 21
4. 19
5. 23
6. 95
7. 26
8. 61

Before I learned how to obtain the data, I purchased a kit to recharge the system with R134. Oddly, the system would not take a full can, and the left side vents seem to blow warmer air than the right side vents. I've read that this may be a sign of not having enough refrigerant causing one side to be dominant / primary. I've also read that the "duo valves" may be faulty, where one should remove the popets, clean and re-lube. I've not done this, but it may be my next action, if I don't get some feedback from the forum. Unfortunately, I have not purchased new hoses / adapters for my manifold...still R12, so I can't really see what the high and low side pressures would read. But, if the computer is reading the refrigerant pressure on the high side properly (26 bar / 377 psi), I would say this is too high. Do the above number indicate I have too much refrigerant in my system.

I would really appreciate some wisdom in helping me solve my A/C problems...any help is welcomed. Does anyone know what may be causing my problems?

Musikmann

How was your A/C behaving before you added the gas?

From everything I've read #7 at 26 is too high. And I don't think you have r12 in a 1997 car. All cars legally sold in the U.S. use r134a as of 1993.

I would borrow a good gauge, remove some of the refrigerant (at least to below 20) and look at the duovalves. See if they move freely and/or are dirty.

Lastly, MB A/C systems are not "proprietary". Any good A/C shop should be able to help.

Good luck.

Shadow5501

Yes, #7 is way out of whack. I've never seen it higher than ~16 bar on my 210 and 211 cars. This would indicate that you are overcharged, assuming the reading is correct.

How long had the system been running when these values were taken? The evaporator temperature is 23C, you are barely getting any cooling. The evap temp should stabilize just above freezing - perhaps 2 degrees C.

Everything else looks reasonably normal, with one small exception. The left (#3) and right (#4) heat exchangers are colder than the evaporator (#5). The air flow is through the evap first, then the heat exchangers.

At this point I think your best option is take it to a shop, have the system evacuated and charged by weight, then see what performance you have.

Chris Carson

Guys, thx for your inputs...

Before I put in the last shot of R134, the A/C would blow cool air (not super cold, as it should) but only when cruising down the highway for a while. Now, since I've added more R134, I'm almost confident, I've "overcharged" the system...especially with the high pressure reading on #7 and because there virtually is no cool air coming from the vents.

The internet website where I got the instructions to pull the temps and pressure data stated to let the car idle for at least 3 minutes...I usually waited a little longer. I pull 6 sets of data...all generally in the same range. As of now, the trouble codes have not reappeared, and let's hope they don't.

I will discharge the system until my #7 pressure is in the 16-20 bar range or I see condensation appear on the low side...but only after I disassemble the duovalve to inspect and clean. Question...with R134, can you still observe the low side lines near the evaporator and see condensation? This was a sure sign that you were getting the pressures right.

BTW, the car has R134, not R12. I only mentioned this refrigerant, as this is what I used to work with in the dark ages when I was a JD mechanic.
In any regard, thanks for your help! If this doesn't do the trick, the old "won't let anything get by me" kind of guy will probably continue to resolve this problem. Keep posted.

ohlord

with the duo valve it is not your problem.
Is your compressor running?
You can't go by pressure to check fill.
If compressor is running and you have some cooling do yourself a big favor and have the system evacuated reclaimed install a new drier and have it charged to the weight and oil amount indicated on the decal located by the ecu.
At this point this will discover if you have a leak and at least let you know you are not over charging the system

Shadow5501

+1

The data you posted do not show the left/right heat exchangers as warmer than the evaporator. This indicates that the air stream is not being reheated, and hence the duo-valve is fine.

The high side pressure would indicate the compressor is fine. I think you likely have a bad expansion valve.

Chris Carson

Musikmann, ohlord and Shadow5501, thanks for the feedback. I just invested in a new A/C manifold gage set and am attempting to hook up the high and low side hoses from my manifold, so I can diagnose my problem. The low side is easy but I'm having trouble finding the high side port. Can you direct me to the high side port? I'll need to get my mirror and follow the high side line (smaller diameter) from my compressor and see if I can locate. Is the HS port, by chance, under the wiper cowling near the expansion valve?

Before I start my E320 and engage the compressor, I want to check the static pressure. What should the static pressure be at approx. 100 degrees F? If the static pressure (should be equal both high/low) is high, is this an indication of the system being overcharged? If you may remember, I tried putting in a can of R-134a and it would only take 2/3 of a can, making me think overpressurization may be part of my problem.

I've asked a lot of questions, but as you may notice, I try to work on my system in spurts between the other hectic things going on...

Thanks again for your inputs...greatly appreciated.

RichardM98

Chris do yourself a favor and follow Ohlord's advice and see an A/C technician. A/C isn't a good DIY project especially when messing with the high pressure side.

If you decide to take it in, I'd suggest having an overnight vacuum test done.

Chris Carson

Richard,

About 25 years ago, I was a John Deere mechanic, where working on R12 systems were my specialty. Due to career changes, I haven't really had a reason to get back into the A/C groove. With plans of keeping my '97 E320 and an urge to get back into the A/C repair arena, I've opted to tackle this project without having to send to an A/C technician and, where I would likely drop at least $500. To support my efforts and your suggestion to put the system under a vacuum, I've recently converted a mini-fridge compressor into a vacuum pump for this very purpose. When I diagnose the problem(s) and should I have to break into the system (high probability, I will), standard protocol is to replace the receiver drier prior to drawing down the system. The length of time you suggest is also taken under advisement. The longer the system is under a vacuum, the better you can rely upon the system being free from moisture.

Now back to my original question and in an effort to save a little time, can you point me to the high side port location? I would rather not have to disassemble unnecessary portions of my E320.

ohlord

coils in front of the radiator.
Although hs and ls pressures will be of little value on the variable demand system.
It does not cost $500 to have an a/c evacuated,recovered,checked for leaks,recharged properly to correct weight.
Applaud the effort however if your system is running and a minor issue like correct fill is causing a long hot summer to become longer and hotter
You know what you need to do

Chris Carson

You're probably right...I'm spending way too much time trying to get up to speed on my E320 A/C system. My time could be devoted elsewhere, but knowing / figuring out how to crack the nut is more challenging than letting someone else do it. My E320 is not a primary vehicle, so I can take my time to fix this problem. But as you suggest, I'll see what a "normal" fee would be for comparison.

Do you have to remove the front grill or a portion to get to the port?