Keyless entry doesn't work on hot day
 

I have a 2003 C230 Kompressor. The weather here turned hot and my keyless entry stopped working in either I/R or R/F mode. Every morning, when I go to the garage it works, but by lunch after the car has sat in the parking lot it stops working. I replaced the batteries on my remote, no help. I am thinking that whetever module that controls the remote is going bad, but where is it? Any thoughts or ideas would be a great help.