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1990 300E
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Discussion Starter #1 (Edited)
Gents,

Hope y'all are staying cool this summer, cause we ain't :( I have replaced the sensors, rebuilt the a/c compressor and trying to decide if I want to disturb the expansion valve. It's a minor PITA that I don't mind but I wonder if it's worth replacing it. A brand new expansion valve is sitting on the shelf but I'm conflicted :eek: Unfortunately, this car came to me with a depleted A/C system so I don't know if the EV is ok or not. Thoughts?

Before I evac the system, I decided to use nitrogen to pressurize the system to 40psi on the low side. I'll leave it this way over night and see if there's a leak on this side of the expansion valve. If all good, then I'll do the same thing to the High pressure side. I might bump up the pressure on the High side to 80 psi unless I'm told otherwise.

My thought for doing this is that I feel that the O rings typically sit under pressure, not under vacuum. If I don't have a leak using this positive pressure test, I'll evac the system and look for leaks. If no leaks, recharge the system. Sounds logical?


A simple gauge setup with a schrader valve.
IMAG0673.jpg

Nitrogen tank setup
IMAG0674.jpg

I'll update this thread with more info tomorrow.
 

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E320/E250 Bluetec Ford F350 6.7l
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The low and high side is the same system. What makes you thinking you can charge them separately?
Usually vacuum test is sufficient for leaks. If the system holds vacuum, you have about 99% chances it will hold the pressure. I understand you don't want to risk precious R12, but why complicate the job?
 

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1990 300E
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Discussion Starter #3 (Edited)
The low and high side is the same system. What makes you thinking you can charge them separately?
Usually vacuum test is sufficient for leaks. If the system holds vacuum, you have about 99% chances it will hold the pressure. I understand you don't want to risk precious R12, but why complicate the job?
I couldn't recall if the expansion valve stays closed normally or not. In any case, the plan wasn't to charge separately, just wanted to make sure that the high & low side will hold positive Nitrogen pressure.

Using positive pressure and soap spray technique to find leaks is a common method for leak detection in a closed A/C system. Given that the system normally sits in a positive pressure environment, it's easier for laymen such as myself to find leaks using positive pressure. It's too difficult to find leaks using vacuum methodology I think; you know there is a leak but don't know where it is. The system has no UV dye in it so I am unable to find leaks that way. I don't have a fancy R12 sniffer so that's out for me as well.

This is my preferred method for finding leaks in automotive A/C system. You can read more about it here: Vtech leak detection methodologies. Look at section 2.2 and 2.3 for more details.
 

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04 odyssey (265k) 1995 E320 wagon (295k)
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Dont forget to drop a new drier in there.
Sounds like you are on the right track, O-rings can fail under vaccum.
 

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1990 300E
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Discussion Starter #5 (Edited)

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04 odyssey (265k) 1995 E320 wagon (295k)
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Tough call, the part is cheap enough, so I' d say do it. Just with a good known MFG part.
Is the A/C system clean of foriegn matter? Did your compressor die and shed crap in the system? If so replace it, no question. Replacing it you should be confident that you dont have to open the system again, due to valve clogging.

OTOH, if you replace it with some cheap knockoff it may fail and require opening up the system again.

bottom line, do you want to evac/fix/refill system over a $30 part if it fails? I know I'd just replace it, lower my odds of something going wrong in the future.
 

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1990 300E
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Discussion Starter #7
Tough call, the part is cheap enough, so I' d say do it. Just with a good known MFG part.
Is the A/C system clean of foriegn matter? Did your compressor die and shed crap in the system? If so replace it, no question. Replacing it you should be confident that you dont have to open the system again, due to valve clogging.

OTOH, if you replace it with some cheap knockoff it may fail and require opening up the system again.

bottom line, do you want to evac/fix/refill system over a $30 part if it fails? I know I'd just replace it, lower my odds of something going wrong in the future.
I have the EV already just wanted to make sure that it was worth the trouble of replacing it. The trouble is when you open up the original A/C system in our aging cars, I worry about not being able to re-seal it properly, even with new O rings. I probably should just do it and forget about it.

The A/C system was leaking around the compressor so I believe that was the cause of A/C failure.

I have six cans of R12 and I believe the system takes 1.5 cans? If so, I have some cushion if I need to revisit.
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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An R12 system takes 2.4 lbs of refrigerant.

Jayare

Sent from my DROID2 using AutoGuide.Com Free App
 

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04 odyssey (265k) 1995 E320 wagon (295k)
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Refrigerant and oil quantities should be on the sticker in engine bay.
 

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94 E320 Cab, 93 400E, 87 300TD, 92 300CE24 Sportline, 94 SL320, 92 500E, 99 SL600R, '02 CLK55
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I would replace the expansion valve; it's not that hard, though I do recall having a bit of a challenge selecting the correct size replacement O-Rings. Access is better if you take out the plastic piece that is adjacent to the ventilation grill and the rear of the engine (I figured this out after I had replaced the expansion valve and was replacing the blower; some of the interference removal for the blower job really opens up access to the expansion valve).

In my case, I had a compressor failure so I was worried about the expansion valve being clogged by foreign matter/compressor parts. I had to remove it anyway to clean the evaporator prior to evacuation and refill.
 

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1990 300E
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Discussion Starter #12 (Edited)
*** update **

well, I recharged the system with two cans of R12 and going to wait and see what happens before I add the remainder. So basically, I left out 14.4 oz, or a whole can. I have a can of Clipline A/C leak stop and also some UV dye that need to go in if all goes well.

I've never operated the A/C system in this car but everything *appears* to be working fine. I guess my DIY rebuild of the compressor is doing ok since I found no leaks during system pressurization with Nitrogen. Compressor is nice and quiet.

This system hasn't been operated for some time as evidenced by the smoke coming out of the aux fan ballast resistor! :D I'm guessing that my engine de-greaser is finally burning off of the resistor! Current clamp showed a draw of 12amps :eek: during the aux fan operation.

Anyway, here are the stats:
ambient temp: 76°
low press 30psi
high press 250
rpm 1300 rpm
vent temp around 40°

Note: I was only able to pull a -20 (PSI or InHG?) vacuum at my elevation of 6850'. Again, not sure if the gauge is accurate or not. Normally, I can pull close to -26 on my R134a equipped vehicles at this elevation so not sure what's happening here. The system held this pressure rock solid for 15 hours so that should be a good sign I guess.

Hopefully in the next few days I'll have a chance to run into ABQ and tax the system a little bit.

According to this site, http://www.ackits.com/aacf/ptchart.cfm, at 76° ambient temp, the low press should be at 16psi and the high at 160-190 psi. Obviously my pressures are higher than that and not sure if I should be concerned about this. I don't know the calibration on my gauges as they're used so that's one unknown.

Let me know your thoughts.

Thanks.
 

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89 300E; 00 E320
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Looking good. It is my understanding that with these models it is more about the amount of R-12 that is put in, more than it is about the pressures that you are getting. Make sure you have close to1100 grams of the stuff in there and you should be right.

I would say that if that can you left out was part of the 1100 grams required, that you put that in now.
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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Looking good. It is my understanding that with these models it is more about the amount of R-12 that is put in, more than it is about the pressures that you are getting. Make sure you have close to1100 grams of the stuff in there and you should be right.

I would say that if that can you left out was part of the 1100 grams required, that you put that in now.
+1.. You need all the required R12 in the system (1100 grams = 2.425 084 884 lb, lbs). At that point or very near it, the sight glass on the receiver/dryer will clear up. If you detect leaks, the ClipLight Super Seal you mentioned is an excellent product. I introduced it into my 400E almost 4 years ago. Vent temps at this time of the year in Florida are at 38 degrees.

Jayare
 

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1990 300E
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Discussion Starter #15
Just a quick update:

I put in the last can of R12, third can, and all is well. Vent temps are around 40deg or lower, depending on the driving conditions.

I am hearing a faint sound coming from the compressor when it's engaged (can be heard from inside the cab). Nothing obnoxious or anything, but a faint groaning (for lack of a better description) sound. It goes away the moment I shut the climate control to ECON or OFF positions. Is this normal?

Secondly, the engine does "feel" the engagement of the compressor. When the compressor is shut off, the car picks up a tad - typical sensation when a heavy load is removed. Is this typical for these cars? The Sheila refuses to use the a/c unless the temps are near the mid 90's or higher due to the fuel economy hit, LOL!

I wonder if putting in the third can has caused the head pressure of the compressor to go high (probably normal) for a system that's still original and probably a little tired! I suppose I can always hook up the gauge set and observe the pressure for a more objective feedback.
 

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1990 300E
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Discussion Starter #17
Mine grones too and it's a brand new 4S compressor.
Oh, no kidding? Interesting, must be a common characteristic with these things. I won't worry about it then.

Curious, does your engine bog down a tad when the compressor is engaged too?
 

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1988 M-BENZ 300E | 1991 FORD PROBE GT TURBO | 2003 FORD EXPLORER 4x4
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Oh, no kidding? Interesting, must be a common characteristic with these things. I won't worry about it then.

Curious, does your engine bog down a tad when the compressor is engaged too?
Yep. Since I have my compressor clutch on a manual switch because the RPM sensor won't work right, turning the compressor off while accelerating is a little like a small shot of nitrous oxide lol.
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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It is very normal for you to feel the "hit" of the compressor engaging on a M103. At the best of times, the car had approx 180 hp. The compressor will have a parasitic drag of approx 5-7 hp, so that is in the range of 5%. Groaning isn't a characteristic of 100% healthy compressor. You've done a good job on the rebuild, just keep an ear on things.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Agreed, you can feel the compressor engagement with the M103...mostly while idling, although the engine management system does a good job of keeping the idle steady & consistent. And NO it's not normal to hear your compressor "groaning"....whatever that means in the noise vernacular of things.:rolleyes:

Kevin
 
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