Was at a tech session this Sat. Looked at pressures on 134a AC(converted a few years ago.) 40 on low side and 250 climbing to 300 on high and pressures dropped whenever fan started-cycled appropriately. Ambient temp 80F. Evacuated system and had .96 lbs-recharged 12 months ago with 1.92. Recharged with 1.90 lbs and same pressures. At idle did not get very cool- 50s. Tech said there must be an obsruction to flow. What would cause this? Receiver drier prob? Of note is that when I went home going 60 mph the temp came down to 40-42F with an ambient of 86F.

Is the condensor clean? Could be the expansion valve, I recall they require some sort of insulation to keep them working proprly.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Maybe some of the experts can chime in here, but that all sounds normal to me. After all, it is a converted R134A system (87 was R12) and it will never be as cold as it was originally.

I have the same situation with my 380SE which was converted professionally about 9 years ago. On Saturday it was just under 90 degrees here, and the converted system was just what I would call "adequate." This was during stop-and-go low-speed driving around town. Although two of us in the front were fine, a back seat passenger did complain that it wasn't cool enough for her. The system is charged properly with almost identical cycling pressures to what you described, and I'm guessing vent temp was around 50. When I drive the car to/from work, the vent temp is somewhere closer to mid/low 40s and it feels great, but I average 45 to 55 mph.

My 300E, on the other hand, has original R12 and it will freeze you if you let it.

I'm going to tint the windows in the 380SE to see if the cooling is improved. If not, I will consider converting it back to R12...

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

I'm certainly no expert on this, but will share my recent experience on the subject. I also have a 1987 300E (98,700 miles), purchased 12/05. I had a refrigerant leak at the compressor (which appeared to be original), and the system had been retrofitted to 134a in 2001 by previous (original) owner. I put on a new (rebuilt) compressor with 6.5 ounces of mineral oil and a new dryer, evacuated the system for a period of about 14 hours, then let the pressure hold for 2 hours with the vacuum pump off. Having no apparent leak, I put in three 6-ounce cans of Industrial 12a refrigerant. The sight glass was clear, and the inside temperature was quite COLD. Colder even than R12, six ounces of this stuff is equivalent to 18 ounces of R12, or to 16 ounces of 134a, and it is compatable with either. Made for automotive use, it is also compatable with all refrigerant oils, but mineral oil is best, as it absorbs less moisture. No license required for this product. Made in USA and totally environmentally-friendly.

Not selling the stuff, just sharing some information on a popular subject.

I am not familiar with Industrial 12a, whatever that is, but...

I would say that charging by sight glass is not the most accurate way to do things. Sure, the A/C may be blowing quite cold - I don't doubt it. But without knowing what pressures you are running, you may possibly be damaging or prematurely wearing your compressor. That sight glass was designed with R12 use in mind and is only to be used as an indicator when that particular refrigerant is in use.

I can tell you with a certainty that R134a runs at much higher pressures than R12, and if you put an equivalent charge into your system or charge to "clear" at the sight glass, you WILL damage or prematurely wear your compressor. I can charge up my converted system to approx. 250 to 275 cycling pressure on the high side, and the sight glass is all foamy. If I were to charge with more R134a until the sight glass was clear, that would put my pressure readings somewhere in the 350 to 400 or more range, if the pressure switch didn't kill the compressor first. Think of what kind of pressure that would generate at 3000 RPM! Evidently you feel comfortable not knowing the pressures your system is running, but be advised you may be setting that new compressor up for early failure.

I would suggest checking the temperature/pressure charge for that refrigerant before running a clear sight glass with it. Also, do a search on alternative refrigerants here, there has been plenty of discussion by the experts. Bottom line is that most if not all alternatives are actually blends of other refrigerants which leak out of the system at varying rates, resulting in inconsistent mixtures and the need to completely evacuate and recharge (rather than top-off). Also consider the possibility of contaminating recovery supply if the fittings are not properly changed on the system, per EPA 609 stipulation.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

The sight glass was the secondary indicator. First was the pressure, which was 75psi with just under 18 ounces installed. Ambient was then 75 F. Look at www.autorefrigerants.com, then ES12, and that will lead you to Industrial 12a.

There is a little bit of Black Magic in charging an R12 system that has been converted to 134. To begin with, you should only charge with about 80% of the original R12 volume. Secondly, there is a point where if you add just a little more R134, the high side pressure will "run away." You do NOT want to hit this point.

If there IS a restriction, I don't think the expansion valve would be suspect. If it WERE the culprit, it is your restriction device in the first place and the low side would get lower and the high side higher, not both sides getting higher.

Good luck Doctor Eric,

Sir
It is nice to hear from you.
1.9 pounds is about 80-85% of the R12 fill.
Also when is the next Dallas dinner with Suginami and 71 R Code and all others?