190D AC question - PeachParts Mercedes-Benz Forum

LRazaitis · #1 07-12-2011, 06:59 PM

Have a 1984 190D, 2.2 engine. Converted over to 134A. Pressures seem high. Have about 50 psi on low side and 350 psi on the high side. This is with the engine running about 1800 rpm. Put in 24 ounces of 134A. Thought the refrigerant capacity was more than that. Was concerned about adding more with the pressure readings I was getting. System seemed to hold a good vacuum. Do not believe there is any air in the system. Condenser coil is clean. Did not replace the dryer, probably should have.
Seems to cool okay after a bit of time.

Thanks for any help.

leathermang · #2 07-13-2011, 01:34 AM

What is the listed capacity of your car with R12 ?
Typical fill of R134a would be 80 percent of that weight.
You should be concerned and not add more until you investigate further.
Why did you not replace the drier ?
' cooling' is subjective unless you use a thermometer in the center vent... you need to do that with the gauges attached and the chart for ambient temperature to compare...blower into front of car, engine high idle, windows open, blower on LOW...
Should read the AC sticky at the top of the page....

piccolovic · #3 07-13-2011, 10:10 PM

. . . was converting my 84 2.2L 190D to 134A. It was such high pressure it actually broke the bracket for the alternator, not once. . . but twice. Once I had a new Mercedes Rebuilt Nipondenso conpressor, and all the leaks were fixed, and the expansion valvesl replaced, I should have gone with my gut and gone with Freeze 12. The AC system did hold up, and I had the pressure checked twice, and was told that the pressure was good, I just never could tryst that I wouldn't wind up busting another bracket (up to three weeks to find replacement) again.

leathermang · #4 07-13-2011, 10:19 PM

How in the world are you going to blame the pressure inside the AC system with breaking an alternator bracket ?

Freeze 12 is Part R134a and is a blend... a bummer if you have any leaks..as the whole thing has to be evacuated... can not just top off like R134a or R12 which are not blends...

piccolovic · #5 07-14-2011, 01:48 PM

The pressure was so high, that there was so much tension on the serpentine belt, pulling on the alternator . . . that's how it happened. When I had the valve job done, my mechanic saw that the second bracket was about to break . . . he removed it and welded it so it was stronger than the belt. He had his A/C guy check and there was a lot of pressure on the whole system. That's why on this car, I only put Freeze 12 in it after putting in the new compressor/dryer.

1980sd · #6 07-14-2011, 01:58 PM

Quote:

Originally Posted by piccolovic

The pressure was so high, that there was so much tension on the serpentine belt, pulling on the alternator . . . that's how it happened. When I had the valve job done, my mechanic saw that the second bracket was about to break . . . he removed it and welded it so it was stronger than the belt. He had his A/C guy check and there was a lot of pressure on the whole system. That's why on this car, I only put Freeze 12 in it after putting in the new compressor/dryer.

Good to know.

leathermang · #7 07-14-2011, 02:07 PM

No, sillyness....
and to boot... now you have R134a PLUS something.. making it a BLEND... which will be hard to find shops to service it, ,make it so that any leaks mean you can not just top it off...but have to evacuate it put the right ratio back in... as a blend leaks the smaller molecules faster than the bigger ones..
There was something wrong with the installation or construction of the bracket... the pressures in the system did not cause the bracket to break...

LRazaitis · #8 07-15-2011, 12:56 AM

Think I will replace the dryer, flush the system and go back with R 12. With the high head pressure it is really taking a lot of HP to drive the AC compressor. Car is not much fun to drive.
Head pressure should be much less with R 12.

piccolovic · #9 07-15-2011, 02:15 AM

Quote:

Originally Posted by LRazaitis

Think I will replace the dryer, flush the system and go back with R 12. With the high head pressure it is really taking a lot of HP to drive the AC compressor. Car is not much fun to drive.
Head pressure should be much less with R 12.

I will admit that I shut off the AC on freeway onramps, but once I got back to third gear, the AC went back on!!! It does slow down the car a lot and it does not like to sit for very long at idle with the AC on.

There was enough pressure in the Nipondenso compressor, that it took a lot more HP to drive the compressor than when it was R-12, hence the pressure on the belt and down the line the alternator. And it happened to two alternator brackets, not one. The fact that it took quite a while to locate another good alternator bracket from a junkyard after the first bracket broke, cause many others were also in bad shape, should say something.