Quote:
Originally Posted by funola
One thing you didn't mention is did you clean your evaporator? I added some 134a to my 85 R4 300 D and got down to 45 deg F at an ambient of 95 F (at idle). I think mine will go lower still with more tweaking. R12 system on yours should do better than that.
An easy way to check the mono valve is the hoses to/from it should not be hot when the temp dial is on full cold detent.
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You're right. I haven't done anything with the evaporator other than flush it internally. From what I've read, getting to the evaporator seems to be a daunting task. Is there a fairly easy way to clean the outsides of the evaporator without having to pull the dash apart to get to it? The idea that the evaporator is dirty has been in the back of my mind since I began this project.
Quote:
Originally Posted by Whiskeydan
The worst piece in the W126 AC is the condenser. Late '84 and '85 models received an upgraded split tube and fin type. This one has approx fifty 6mm tubes as compared to the early version which had half as many passes with much larger tubing.
My 'Black' '85 300SD with its stock AC has no problems keeping the cabin uncomfortably cold at any ambient temp below 97f using R134. It has the late version split tube condenser.
Earlier W126s I have owned had marginal AC with R12.
You may have received the early version condenser which would account for the lack of performance. Also, these systems are sensitive to the amount of oil installed. Too much is not better.
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My condenser has about 28 round tubes going through the fins. The fins are very thin and flimsy, but I believe there are more fins than the factory condenser. If memory serves me correctly, my OE condenser is of the same type, and I believe my 300SD was manufactured during the first quarter or so of 1984.
As far as oil is concerned, I know that I have no more than 8 ounces of mineral oil in the system. I've seen varying amounts listed as the right amount (anywhere from 6 to 10 ounces as acceptable) from others online, but nothing from MB stating an exact amount when starting from scratch.
Quote:
Originally Posted by ROLLGUY
I had 5 kits on a summer special, but all are sold. I still have everything available at regular prices. I hope to offer only 7 cyl compressors when my supply of 5 cyl units is gone.....Rich
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Too bad, I guess. Do you have a link or site where you list all the parts you sell and have available? I'm not opposed to replacing some parts if they're far-superior to the OEM stuff.
Quote:
Originally Posted by jcyuhn
He has reasonable cooling at road speeds, it's the idle that's not so great. With a low side pressure of 55PSI there is no way to get good cooling at idle. Recall your middle school science class - the boiling point of a liquid varies with pressure. Lower pressure equates to lower boiling point. In the case of R12 the temperature at which it boils is approximately equal to the low side pressure (expressed in PSI) - one of the cool things about R12. Hence his evap is only at 55 degrees at idle, and the air coming off it is typically ~10 degrees warmer, depending of course on fan speed. Here's a link to R-12 & R-134 pressure/temp charts: http://www.ackits.com/aacf/ptchart.cfm
My 123 300D had the same OM617 & R-4 combo, and I had the same challenges. It was OK at speed - not great, but OK. At idle it really didn't cool well enough and the car really wasn't comfortable in the heat of a Dallas summer.
My solution involved selling the 123 and acquiring a 124. |
The vent temperatures are decent (not great) if the ambient temperature is below 80*F or so. Yesterday, the temperature outside was 95*F and the A/C vent temperature was only 58*F while cruising, which jumped to 68* while stopped, so not that great. This morning, the outside temperature was 74*F and vent temps got down to 40*F, which was nice. 40*F at the vents seems to be the lowest I've been able to reach, regardless of outside temperature.
Previously in the thread, the idea that the freeze switch might be incorrectly adjusted. Does anyone have any additional information with respect to the freeze switch? Does it even sound like it might be the culprit (or at least part of the problem)? I think I found it up under the driver's side kick panel, but I'm not certain, and I definitely don't know what to do with it to adjust it.
Thanks for all the help and suggestions. I forgot to check temp of the tubes going in and out of the mono valve when I arrived at work, so I'll check them after the drive home and report back.
Thanks.