89 300se w126 ac questions,issues.
 

I broke down yesterday an bought a pair of respectable ref gauges. :D I was so sick of under charging/overcharging my ac system. I drained my system, removed my dryer, an blew air through to clear it out. I then re assembled, pumped down, added oil, then freon. (r134). After the third can (I remember reading in a previous thread that is was 3 cans) Im reading 10psi on the low side and 200psi on the high side. Ac is all but disappointing. What are the recommended pressures for this car? Do I need more freon?

Has anybody heard of a refrigerant called MAXI FRIG? I use it in home refrigerators with great success, but I am nervous to install it in my mercedes.

My brother put it in his audi about 2 years ago and says its the best.

You cant blow air throught the dryer. If its old or open to the atmosphere, it needs to be replaced.

You are missing a few critical pieces of info. Ambient temp? RPM? Vent temp(s)? You need to quantify "all but disappointing."

Looking at my log, my W126 380SE pressures were 27/325 @ 2500 RPM 98 degrees ambient. I don't know what your ambient is, but the pressures seem a little low to me; they read more like R12 pressures, except the low side is too low (needs to be near 30). My log shows I used 3 cans of 12 oz. R134a, for a total of 36 oz. IIRC, this is about 75 to 80% of actual system capacity. My vent temp readings a few days later were 62 idling, 48 moving, 86 degrees ambient.

Keep in mind that the system was designed for R12. Using anything other than R12 in it will produce less than optimum results.

I didnt check temp. Last night it was about 80 degrees, my vents were blowing just slightly cooler. (65-70?) I may want to measure that this evening. Pressures were at idle, 650 rpm or so. At what rpm am I supposed to check pressure? I always assumed at idle, but then again, I never had good ac.

I thank you all for your help. I am very grateful to be a part of this forum.

I would check pressures between 1500 and 2500 rpm.

just to recap:


27/325 @ 2500 RPM

ambient temp will be around 80 degrees today. Do I need to make any adjustment for that?

I will try adding this new freon. I will let you know if it helps or not.

Blowing air through the receiver/dyer was a bad thing. It's now loaded with moisture. While you have it off to replace it is a good time to replace the two sensors mounted to it. You want to move quickly when replacing the receiver/dryer. It becomes contaminated by moisture in the air very quickly. Once you have it back together you also need to connect a vacuum pump and pull a vacuum for about an hour to remove any remaining moisture. If you don't the system will never cool.

When you recharge it with R134a you need about 75% of the charge it had when it had R12 in it. The Original charge was 1300 grams, so 975 grams of R134a should do nicely. That's about 3 ounces less than 3, 12 ounce cans.

That sounds about right. I wouldn't add any more, maybe take out an ounce or two (you'll have to guesstimate that).

Beyond this, there is nothing else that can be done to improve the situation, other than converting back to R12.

leak.
 

As I was charging, and getting disappointed, I noticed some bubbling coming from the compressor. :( I guess its time for me to look into the r12 conversion. Is there a thread anywhere that someone can point me to in regards to doing this properly? If im going to be removing my compressor etc, I really only want to do it once.

Im not really disappointed, ac with 134 really sucked anyways.

Is it leaking from the front seal? Do some research - you can usually replace the seal rather than the whole compressor. Would be a lot less expensive, and there's no point replacing a compressor that's still capable of producing 325 psi.

The leak seemed to be coming from the back. Not where the flange bolts to the ac unit, but a little further back on the line. I wont be changing my compressor, but I think removing it an cleaning it proper id the way to go.

when you remove the compressor,replace all four of the "O" rings below the flange where the pipes hook up.you are dealing with a nippondenso compressor and that is a common leak point.based on your first post i would also suspect the expansion valve as being partially blocked.also on the drier there are two sensors,the one with the pigtail is for the aux fans.disconnect those short wires[male spade connectors]and plug a 10 amp fuse into the two female sides.this should make the aux fans run as soon as you turn the ignition on.this will help the condensor do it's job.

David,
Do you leave that 10 amp fuse in the pigtail for aux. fans indefinately?