AC help please!!!! - PeachParts Mercedes-Benz Forum

051 · #1 06-25-2010, 06:49 PM

83 380 SEL
ambient temp in shop is 81
temp at vent with ac and fan full out 60 f
Low side psi 45
high side psi 250
See a fair amount of bubbles, looks like foam, in sight glass
temp of high side hose going into firewall 145
temp of low side hose coming out of firewall 87
top rad hose is 155 f
hose going into condenser is 146 f'
hose coming out of condenser is 143 f

new:
compressor
exp valve
dryer
system newly charged with r 12
Not sure about the amount of oil the mech put in but I am sure he added oil to the compressor before charging the system.

flushed and blew out all lines

heater hoses pinched off at firewall just to make sure no hot water is getting through firewall.

What am I missing here?

Any help will really be appreciated. If I can't do better than this I'm going to sell it and give up.

Thanks!
51

Gilly · #2 06-25-2010, 08:57 PM

Maybe low on freon? You have bubbles or foam and don't mention how much was put in. Usually bubbles and foam mean low freon and poor performance. Is the aux fan running? What is the output like when driving? Where are you getting R12, are you sure it's not some crappy drop-in refrigerant. The kind that goes BOOM?
Gilly

dpetryk · #3 06-25-2010, 10:05 PM

Based on the temp readings on the condenser lines and the pressure on the high side, I would bet somebody used 134 instead of 12

051 · #4 06-27-2010, 07:01 PM

can someone tell me what normal pressures and temps would be?
Also what is the max pressure on the high side. I want to add some more freon and see if the bubbles go away, I assume this will increase the pressures, but I don't know what the limit would be.
Thanks!
51

dpetryk · #5 06-28-2010, 08:37 AM

There is no "normal". Everything depends on the ambient temperatures and air flow over the condenser & evaporator. If you have bubbles, then you need more freon. In my experience, after the bubbles go away the system needs about 1 lb. more to meet the specified requirements. Many people just add freon until the bubbles quit. I have found that is not always an accurate indication of the charge level. Usually it is good enough for most situations especially if you do not have the tools to accurately charge the system.

051 · #6 06-28-2010, 10:31 AM

OK, I'm going to put more in and see what happens.
Thanks!
51

mbdoc · #7 06-28-2010, 11:09 AM

Have you checked the fresh-air / recric flap for proper operation?

IF that door doesn't close all of the way the a/c duct temp can be 5-10 degrees off.

tinypanzer · #8 06-29-2010, 10:52 AM

MBDOC is right, especially when the hood is up if the recirc flap isn't closed, then you're sucking in super hot engine compartment air. Even if that is happening, you should see water puddles underneath the car if it is cooling at all.

Are you doing this at idle, or at 1500rpm? 1500rpm is a much better way to do this. If you still see bubbles in the sight glass, then you're still probably low on refrigerant.

Also, very important - After the parts were replaced, was the system totally vacuumed down? Air or moisture will kill the efficiency of the system.