AC without a CCU
 

This winter I junked my fried CCU and installed an on/off switch for the blower, and an engine-bay valve for the heater core.

If I want to have AC this summer(assuming all the remaining components are OK) I just have to turn off the hot water; and install a switch to engage the A/C compressor and aux fan?

Also, should I change the oil in the compressor just to be safe?

Find the wiring and CC diagrams for the 240D with a manual system.

Using an on/off switch for the A/C compressor is a guaranteed way to pop a hose or fry the compressor.

Looking into it, I may just scrap the whole AC system and use the condensor as a transmission cooler.

I can't see why it would be so bad to wire it up, as long as you ran through the refrigerant pressure switch to prevent the compressor from starting if there is a large refrigerant loss. That's how they run normally -- all the time.

You should probably install a binary switch in the high-side. You could optionally put a switch in the low side (and just a high-pressure cut-out on the high-side) to help prevent evaporator freezing, as otherwise you will be on manual control for that.

thats a good idea. Another good idea would be to fix the system but wiring in a switch for the ac compressor is asking for trouble

Well, the automatic system does appear to be cycling the compressor on my vehicle. But you are right that until very recently this is how all auto A/C systems ran. There would be a relay in line to make sure that the blower motor had power and that's it. The compressor ran full time and you adjusted the temperature with a manual air blend door that increased or decreased the amount of outside air. It wasn't until the late 70's and early '80's that you started widely having systems that would cycle the compressor. And this was primarily for fuel economy, not that there is anything dangerous about a compressor running.

For a safety measure hook up a relay on the air blower circuit that closes when it is receiving power. Run the compressor control through that relay and through a pressure switch as Matt L. mentioned. You'll also want the electric cooling fan to power up also. I owned a '72 Imperial for a number of years that operated this way for close to a decade when the Chrysler system died.

This link might shed some light on the minimal requirements for AC.
http://www.peachparts.com/shopforum/diesel-discussion/230504-klima-relay-deleted-om603.html

If you make some kind of evap temp switch (that shuts the compressor off at like 38*) then you can just use a switch to turn it on... that would make it like every other "simple" air con system. Of course you also need low and high system pressure cut out switches.

-Jason