AC system upgrade - PeachParts Mercedes-Benz Forum

280EZRider · #1 03-31-2011, 01:38 PM

I have just replaced my old York compressor with a Sanden, which has 10cc displacement less than the York. There is now about 10" less in hose lengths and I am still using R12 as well. The MBZ maximum is 1.2 kg of R12 with original configuation.

I now have a completely evacuated system, 1.9 kg of R12 available for charging, and no pressure gauges.

My question is: Can I still use the 1.2 kg as a max weight?

vstech · #2 03-31-2011, 01:45 PM

yes.
the displacement difference will not factor into total charge. nor will the hose length.

for the gauges question, I'd get a set from the local pawn shop. or go to harbor freight for a new cheapie set.

and it's a REALLY bad idea to evacuate a system and let it sit in a vacuum... pulls in moisture. the schrader valves are NOT designed for vacuum holding.

280EZRider · #3 03-31-2011, 07:04 PM

Thank you. That's what I thought.

So can I use just one pressure gauge on the discharge side while charging on the suction side, or do I need the complete set of gauges?

As far as time after vacuum, it was just done yesterday and I'm planning to charge tomorrow or day after. Is this still too long of a wait? (The schrader valves are capped of course).

lee polowczuk · #4 03-31-2011, 07:44 PM

if you don't have the gauges...it may make economic sense to take it to a shop...have them pull vacuum for a half hour to make sure it doesn't leak....then have them throw the refrigerant in.

it may be cheaper than buying a set of gauges.

280EZRider · #5 04-03-2011, 04:42 PM

In the end the system went only 1 1/2 days between evacuation down to 28 and charging. And since this was not a top-off but a fill from empty, and since I had the exact amount of R12 in cans that the system calls for, "I don´t need no stinking gauges." Plus my system has the added advantage of an over-pressure switch mounted at the receiver/dryer, wired between the compressor clutch and the power source. I did, however, need to have an electric space heater running inside the car to keep the compressor from cycling. It was a cold day in Cincinnasti.

Diesel Giant · #6 04-03-2011, 07:00 PM

Since guages are not very accurate in telling you how much vacuum you have pulled down to, I would run some dry nitrogen throught through the system a few times. If you can borrow a micro guage and get it to about 2000-1000 microns and it holds, then you will know your system is good an moisture free.

vstech · #7 04-04-2011, 10:58 AM

I don't think you can get a reliable micron reading in a mobile a/c system.
dry nitrogen is a very very good way to test for leaks, as long as you have SOME refrigerant in the lines for the sniffer, or you use a ultrasonic tester.
the problem with evacuating a system, then unhooking the pump, and gauges, then hooking gauges back up, then charging is: each time you open the caps, unhook and reconnect gauges, you are putting moisture and noncondensibles in the system. no way around it. you ARE damaging your system.
best to flush out with nitrogen, evacuate again, purge with refrigerant, then evacuate AGAIN, then add in the proper volume of refrigerant.
period.

you NEVER want to leave a mobile a/c system in an evacuated state for longer than the time needed to connect the charging cylinders to the manifold.
period.

280EZRider · #8 04-04-2011, 04:39 PM

John, so accordingly if your system is completely full and moisture free, the sight glass on the receiver/dryer should be absolutely clear with the compressor turning, right?