I'll keep it short and sweet.

Does the aux. fan in front on the condensor come on as soon as you select A/C or does it depend on temperature (i.e. outside temp, eng. temp)

I ran my A/C for a FEW minutes today (not warm outside about 65) and it didn't come on.

Thanks!

BTW '78 240D 4spd.

The fan is actuated by a temperature switch on the receiver/drier. It will typically come on only in relatively high ambient temps and when in stop-and-go driving conditions. You can test the fan by jumpering the leads that connect to the temp switch (not to be confused with the low pressure cut-out switch.)

A low refrigerant level can prevent the fan from operating, as the "trigger" temp will not be attained.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2AT0J1QHK2DB161J73&year=1978&make=MB&model=240-D-002&category=R&part=A%2FC+Temp.+Switch

TangoFox Thanks!

So shoud I look for the switch that looks like the link you provided and jump those 2 leads and see if it turns the fan on?

Thanks

Yes. Connect the two leads that plug into the switch. The switch itself will not be in the circuit. And your ignition switch should be in the "run" position.

tangofox thanks, hey since you seem to be quite knowledgeable, do you happen to know how to check/add compressor oil to a YORK compressor? I understand they carry a sump???

Thanks!