I had a problem filling the ac system with freon after changeing the comp,expansion valve and dryer because the compressor would not engage. I removed one of the wires from the low pressure switch and connected it to a wire from the + battery terminal and the compressor engaged. I let it run long enough to fill with 3 cans. It ran cool after filling and i reattached the wire to the L pressure switch. The compresson did not engage after that. Could a bad fan temp switch cause that. I tried jumping the fan temp wires that go to the fanand they got hot so i quickly stopped. I jumped the fan itself at the plug in and it started. All fuses are ok. The blower works. Any ideas where to check to get the compressor to start functioning. RAY M

sounds like a bad low pressure switch to me, short the two wires on the lp switch and see if it starts

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By short do you mean bridge the two wires together that lead to the low pressure switch. If it is bad am i right that when i replace it i'll need to recover the freon then refill it. Thanks KMAYSOB, i'll try it. RAY M

Have you looked over the pictorial?

http://dieselgiant.com/repairyourac.htm

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YES. That is the directions i used. I got from you the evaporator a dryer, 3cans of freeze 12, frigi quiet, then a side can tap when I discovered the cans were different from 134. Most of the frigiquiet leaked out when i turned it sideways to install the compressor so i added 2oz of freeze 12 oil. I wrapped the expansion valve with something someome called monkey do to reduce condensation on the expansion valve. Was there something you think I might have done wrong or out of sequence that may have caused my problem other than useing the old low pressure switch and old temp fan switch on the new dryer. RAY M

I couldn't have done it without your help. You were great. Thanks DIESEL GIANT
I don't have alot of extra time and have had one thing after another for 6 wks now. Definitly a learning experience. and it still doesn't work. could my on of connecxtions be loose. 6mo ago i was workin behind the console by all of the controlls. But then the ac still worked. Go figure, and still worked but kept leaking. 6 wks ago i started to fix it all. Thanks again RAY M

Yes if you replace the low pressure switch you have to recover the refrigerant. Maybe check your high and low pressure and if they are good then just bridge the switch for now. Get the wiring diagrams and study them well. There are several fail safes to protect the compressor from cooking. Too bad they picked such a crappy compressor to protect

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Doug

1987 300TD x 3
2005 E320CDI

Do you know of a link i can go to to get the wiring diagrams. Those fail safes might be good to know. RAY M R4 rotary compressor on a 1980 300d

I Got Continuity On The Low Pressure Switch And It Still Doesnt Engage The Compressor. Totaly Lost Now.