1999 e300 with error code p0235
 

My wife started the car the other morning and the check engine light turned on, and she said the A/C wouldn't work. I checked the code and it came back (p0235 boost condition limit not reached). I erased the code and the A/C works now. Any ideas on how to troubleshoot /fix this code? I checked the fuses and hoses all is good.

Thanks,
Anton