1416 error code but no A/C
 

My parents bought a super clean low mileage 99 E300 and the only thing wrong with it was the A/C did not work. I pulled up the codes through the climate control panel and the only code showing is the 1416 which is supposedly for the pump that is on the framerail just to the left of the turbo. It is not connected to the A/C system but I have a spare 99 parts car that does not have the 1416 code showing so I will swap the pump out when I get a chance. I put a gauge on the low pressure port by the intake manifold and it shows 29 psi but since the compressor will not engage there seems to be no way to add more to the system using a can from the local store. The compressor is not seized, I can't find any fuse anywhere that is for the system, and there are no other codes.

What am I missing here and what do I need to do?

Thanks

29PSI standing pressure means the system is just about empty. You're probably locked out on the low pressure switch to keep the compressor from engaging. I'd suggest finding the leak before recharging. If you wish to skip the leak search and just dump refrigerant in it, you can charge through the low port even though the compressor doesn't run. With the A/C off, charge a can as a liquid through the low side port. You should be able to get most of the can in there (it'll turn to gas as it enters the system) and should raise the pressure high enough to engage the compressor so you can finish charging.