I replaced my Klima/Kickdown Relay and it did not help. I then replaced my PBC and still no luck.
I bought the R134a kit at Walmart for about $25 which included a gage and bottle of R134a. Turns out my system had zero psi. I recharged the system and I now have A/C.
If you still need the PBC, try:
http://www.benz-store.com/push_button_operating_units.html

They have the most reasonable prices with a 3 year warranty.