Chrysler Repair: Chrysler 300M, pressure transducer, auto parts stores

Question
Bought a 300M for my daughter about a year ago.  The A/C has never worked.  Took it to Jiffy Lube for oil change yesterday and had them do A/C service as well.  They told me the refrigerant level was only slightly low, and would not have been the reason it was not working.  They also advised that the interior a/c switch checked out ok, as well as the pressure and condenser.  They suggested that I replace a switch which is between the interior control panel and the condenser.  Went to two auto parts stores this morning and they could not identify the switch/part for me.  Does this sound like a correct diagnosis? Do you know the part I should be asking for?

Appreciate any assistance you can offer.

Answer
Hi Bill,
The 'ac pressure transducer' is a sort of a switch which electrically tells the ac controller whether there is or isn't sufficient refrigerant in the system so as to give the ok to activate the compressor,  and it is in the refrigerant line that returns from the cabin to the condensor, mounted on a valve in the right front corner of the engine compartment. There is also fuse B in the power distribution center under the hood that activates the compressor clutch so check that out too. Those are the two things to check out. Let me know the model year so I can be a bit more specific/accurate.
Roland