W123 300TD (1982) Air Conditioning rebuild advice - Page 6 - PeachParts Mercedes-Benz Forum

300TD1982 · #76 08-18-2020, 04:25 PM

Added 4 oz of PAG100 to the dryer and installed the pressure switch. Installed in car. This is kind of a pain in a wagon because the SLS tank is exactly in the way.

Purged the air from the system with CO2 and left it at 60PSI. I had a leak from the sight glass in the dryer which I had open to pour the oil in. After tightening that, the system has been holding pressure for about half an hour. I went around with a UV light and don't see any leaks. Gonna eat lunch now, and in an hour or so I'll pull a vacuum.

For some reason my AC manifold kit won't clamp to the high side port. It fits on but doesn't clamp. Not sure why or what to do about that.

resago2000 · #77 08-19-2020, 09:37 PM

a curved blade fan should be quieter.

300TD1982 · #78 08-20-2020, 12:20 AM

I vacuumed it for a few hours and filled with R134a. I don't actually know the outside temperature, so I erred on the low side. I got self sealing cans of R134a, so it will be easy to top up the gas if I need to. The hooptie blows cold air! I don't know how cold, but it felt *good*. I'll invest in some thermometers I suppose.

The electric aux fan is very loud. Outside the car, it's really noticeable.

Thanks for all the help! I'll take some pix at some point.

EDIT: I stuck a meat thermometer in the ac vent. It says it's blowing at 60F. It's 100F outside, so this feels pretty darn good, but I understand that it should go lower? I'm possibly low on R134a charge, so that might be a factor. Also, the fresh air vent is probably open, as I have all the vaccuum disconnected from the climate control (massive leak somewhere). I'll address the R134a charge when a better thermometer arrives next week. As far as the fresh air vent, my plan is to remove its spring and permanently fix it about 10% open, if possible. I kind of hate all the vacuum stuff related to the climate control and I'd rather bypass it all than fix it.

resago2000 · #79 08-20-2020, 09:10 AM

40 degree delta isn't bad, you may get a few degrees higher in optimum settings.

ROLLGUY · #80 08-20-2020, 10:17 AM

A test: Clamp off the hose from the head with needle-nose vice grips (or tool made for this purpose), and see if it makes a difference. It made a huge difference in the last A/C job I did. Even though the mono valve is good, the heater core is above the level of the head, and heat soaks the hoses and core just enough to raise the temp of the air going across the evaporator. For best results, I put a ball valve (3/4 PEX) in the hose above the oil filter stand. That keeps any and all heat from entering the core, and gives the evaporator the best chance to do it's job. A clean evaporator, large cooling fan, and a P.F. condenser should cause the ETR to cycle the compressor, and thereby blow ice cubes through the vents.

vwnate1 · #81 08-20-2020, 11:04 AM

40* out the vents with 100* ambient temp. while sitting still is very good .

Before you add any more R134a, take it for a drive ~ my two working W123's with AC drop the dash vent temps sharply when the car is moving , I think that noisy AC fan in front of the condenser would be better ~

Remember : R134a work best with less in the system than R12 .

ROLLGUY · #82 08-20-2020, 04:10 PM

Quote:

Originally Posted by vwnate1

...................
Remember : R134a work best with less in the system than R12 .

The standard is 85 percent of the R12 charge. However, you have a condenser with a much smaller volume, so even less than 85 percent of the 2.2 pounds the stock system calls for. I have been running 21-26 ounces of 134a in these systems (Sanden+P.F.condenser).....Rich