How to jump A/C compressor

CHARLESTUCK

MEMBER
1985 MERCEDES BENZ 380SL
3.8L
V8
2WD
AUTOMATIC
95,000 MILES

I just installed a new A/C compressor. I have pulled a vacuum and it holds. How do I manually jump the compressor to allow me to charge the system? Is there an alternate method?

Thursday, May 31st, 2018 AT 6:21 PM

3 Replies

STEVE W.

MECHANIC
13,573 POSTS

The easiest way is to just start adding refrigerant until it kicks on in response to the low pressure switch. Usually it will kick on and start to cycle at 3 to 6 ounces. If you still have it under vacuum close the valves and hold it that way, unhook the vacuum pump, connect up a can and let it pull it in through the high and low lines. Then close the high side and start the engine and see if it cycles. If not you can keep adding until it does. Then either charge by weight or read the temperature tables for your current ambient and charge to the proper pressures.

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Thursday, May 31st, 2018 AT 7:02 PM

CHARLESTUCK

MEMBER
59 POSTS

I connected the fron supply after the vacuum process and was able to introduce a small of rfreon until it stopped going in. There is no activity from the compressor. On most other cars you can just jump the compressor wiring and the compressor starts up. Is there a way to jump the compresssor relay or the compressor delay?

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Thursday, May 31st, 2018 AT 7:44 PM

STEVE W.

MECHANIC
13,573 POSTS

Look at the compressor wiring, should be a black wire to ground. Put 12 volts to the other wire and the compressor should engage. If you turn the controls to maximum cold it should not take a lot to get the compressor to kick on. As long as the rest of the system is okay.

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