ATTN: MVAC/AC gurus
 

I'm planing on replacing my faulty A/C temp switch, (and NOT having the aux. fan constantly on.) When doing this I DO plan on replacing the receiver/drier, vacuuming the system, etc. Other than the switch, the a/c works well, no leaks.

THE QUESTION-
While the system is open, is there anything else I should replace "while I'm in there?" expansion valve, pressure switch, etc.

BTW I just got 609 certified yesterday :D

You should consider flushing the system while it's open, to replace the compressor oil. Don't flush any mufflers though - lines with mufflers need to be used as-is if possible, or replaced. Flush the compressor with clean compressor oil only, and never solvent.

Yes, you should replace the expansion valve. As for the pressure switch, I'd go on the price of the unit.

You also may want to replace all the O-Rings. They are cheap and simple to do once the system is open.

How did you diagnose the sw as bad??

PO's receipts from the dealership listed, "aux fan shorted ON, owner will return for temp switch replacement." or something like that.

I see.

Well, I would certainly do a little looking before condemning the sw.
It only takes 1 minute to unplug the sw leads to see if the fan stops. If it does , the diagnosis is correct, but if it does not, it could be as simple as a common stuck relay or even a fan sw by-pass by a previous owner.
Be a shame to open up the refrigerant system for a wrong diagnosis.

This would be the sw. that operates low a/c fan and you just unplug one of the pigtail leads for this test.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2AO123CS42CT18JUFB&year=1987&make=MB&model=300-DT-002&category=R&part=A%2FC+Temp.+Switch