'81 300SD. My Freon is very low or gone. If I run it some to keep the o rings pliable, will I hurt the system? Will it burn up the compressor?

Low pressure switch will prevent compressor from coming on. Low freon should not be a problem.

If you know it's low just unhook the low pressure switch so it won't turn on the compressor. Replace the O-Rings before you recharge.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

OK, thanks guys.

even if it would run, the compressor will not pump oil, it only navigates oil that is dissolved in the refrigerant. no refrigerant, no oil flow...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

VStech - that sounds like do not run it just in case until I get some Freon.

It all depends on what do you mean by running it some. There is a low freon pressure switch in line with the compressor clutch to stop the compressor from running. If the compressor runs then you have enough freon to activate the switch so it is OK. If you jump the switch because of no/low freon to test the system than it is best not to run it for more than 30 seconds.

People jump the switch quite often for a short while - to test the system or do the initial recharge.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Do not intend to jump the switch.

Last summer one of the Atlanta forum guys put in some Freon for me with a pressure gauge. We stopped at something like near correct pressure reading but before the bubbles cleared up in the sight glass; however, it never really gave me cold air. He was concerned about putting in more Freon. I made it until now with no AC. Now I see zero bubbles and suspect the Freon is completely gone. That was why I asked about running it with no/low Freon. My indy no longer carries Freon nor does any station around here. Hate to go to the stealership and ask them to check for leaks and put in some Freon.