SDL AC charge - PeachParts Mercedes-Benz Forum

werminghausen · #1 05-10-2013, 02:57 PM

I was recharging the AC of the SDL today.
System was holding vacuum very well and I was charging R12.
Ambient was at around 100F and I was charging 3 cans, total of 1200g ( with the changing of cans I lost some refrigerant..so my guess is I have 1100g in the system).
Low side pressure was around 130psi (constant, no matter what speed, I guess this is the high ambient temperature) and high side was around 200 - 220 psi depending on engine speed.
The sight glass got clear after 3 cans. Before there were bubble.

However the temperature at the vent was declining but never below 8.5C (47F), then the compressor was cut off. I think it is the temperature sensor sticking in the evaporator causing the compressor cut out.
Compressor starts again after some while. It cycles on and off and the temperature stays at around 47F.

I just wanted to check in with people who know the system well.
Do the pressures make sense? Do the on/off cycles and vent temps make sense?
I am sure I lost some refrigerant during the process of charging and I think I have probably 1100 g in the system....while the sticker says 1300g.
Martin

werminghausen · #2 05-11-2013, 02:05 PM

AC is cooling okay....as I noticed during charging the compressor is cut off as soon as vent temps are reaching 50F...Cooling is very constant and with 110F ambient I think I can live with this. It could be blowing colder but i think this is the temperature sensor in the evaporator causing the on and off cycle of the compressor.
Another thing that puzzled me was the high pressure at the low side (130psi!) This seems excessive. However I believe I had a problem with my low side hose that didn't fully open the Schrader valve and so I had a hard time to get the 3 cans charged. It took me literally hours to get the can filled in. So I believe the low side reading was not accurate.
Martin

alabbasi · #3 05-12-2013, 10:07 PM

Your low pressure side is too high which indicates that you've over charged the system. Low side should be less then 50psi and high side about 2-2.2 times ambient temp.

The system will not cool well if over charged so if you can, evacuate the system by recovering some of the freon you put in there.

I would not trust the sight glass for charging. It's best to use gauges if the system has freon or charge by weight.

Mark DiSilvestro · #4 05-12-2013, 10:18 PM

FWIW, after replacing one of the HP AC hoses in my '84 Euro 300TD, today I charged the system and noticed the factory AC decal gave the capacity for the W123 and W126 as 2.9 pounds.

Happy Motoring, Mark

werminghausen · #5 05-13-2013, 12:08 PM

Quote:

Originally Posted by alabbasi

Your low pressure side is too high which indicates that you've over charged the system. Low side should be less then 50psi and high side about 2-2.2 times ambient temp.

The system will not cool well if over charged so if you can, evacuate the system by recovering some of the freon you put in there.

I would not trust the sight glass for charging. It's best to use gauges if the system has freon or charge by weight.

Hi Al,
You are correct with the low side pressure of roughly 50 I think.
However I charged 3 cans of 400g w/ some loss during putting hoses on and off (the typical fuss with old AC hoses/gauges). I had a hard time to get the Schrader valve open with the pin on the AC hose fitting and the Thread of the male fitting on the low port was run down..so the AC hose fitting wouldn't engage....real trouble if there is pressure on the system and you try and get the old hose on the port....it is a nightmare.

I had no chance really to change and it took me 6 hours to get the 3 cans filled in.

But I am absolutely shure that I didn't overcharge with 1200g... Manual says 1300g is the charge (2.9pounds).
So I need to check the low pressure...if I 'll get a better hose.

High side was right on 100F ambient- 200-220 psi
Martin

werminghausen · #6 05-13-2013, 12:09 PM

Quote:

Originally Posted by Mark DiSilvestro

FWIW, after replacing one of the HP AC hoses in my '84 Euro 300TD, today I charged the system and noticed the factory AC decal gave the capacity for the W123 and W126 as 2.9 pounds.

Happy Motoring, Mark

Correct, the sticker on my car says 1300g R12 = 2.9 pounds I believe.

alabbasi · #7 05-13-2013, 12:15 PM

Did you pull a vac? If the system had air in it, it would act the same way.

werminghausen · #8 05-14-2013, 09:41 AM

Quote:

Originally Posted by alabbasi

Did you pull a vac? If the system had air in it, it would act the same way.

yes, I pulled a nice vacuum.
I need to explore the high readings at low pressure side. I guess if I had a lot of air in the system the cooling would be poorer than it is right now.
Actually the cooling is quite the same as it was before. Initially I thought I could improve cooling and seal the leak (leaking Schrader valve- yes I did) .
I'll check the low pressures again as soon as I have time.