ac & aux fan questions 300E

[schumi]

I know this has been discussed many times but I couldn't find specific answers in searches. Car is 1987 300E.

First problem: ac compressor is not engaging. I can get it engage by grounding one of the leads going into what I think is a pressure switch next to the ac drier - I am talking about the little switch just to the left of the sight glass, with 2 terminals on top. If I ground one of wires going to that, compressor comes on. I tested and found no continuity in that switch - I suspect that switch detects when the freon pressure is too low to run the compressor and prevents compressor from coming on - is that correct? (I suspect I may be low on freon as ac did not seem to cool even with compressor jumped to run as described already).

Second problem/question - I have seen many times people talking about testing the low aux fan by jumping the high pressure switch (I have tested and confirmed high fan works by jumping coolant temp sensor). I have seen it described as red or green depending on the year. I am trying to find this thing so I can jump it to test it - I see a red cylindrical thing that is just below the one I describe above - it is lying on its side and has 2 leads coming out of it. Is that the one I jump? How do I test low fan - by jumpering the leads coming out of it???

Thanks for any help.

[Arthur Dalton]

That is the low speed fan pressure switch...fan should run when wires to that sw are jumpered ...key on...

[jbaj007]

1.) Low refrigerant charge is the cause, usually; you are correct.

2.) jump the two wires that go to the "red cylindrical thing"; fan should start up (low speed), as Arthur said.

[schumi]

Thanks, guys. The drier was replaced last year and ac worked great for most of the summer but it stopped working in fall. I guess there is a leak somewhere.