Why isn't heat / AC working properly after changing AC relay??

in this car, nothing in this CL model is working with the HVAC. Just tonight,
the AC relay was changed, yet there was no response with the air con
system. I noticed while looking at the face plate, that the HVAC system has
both passenger and driver temperature settings. I 'd like to know if there was
a recall for the 98 CL model Vettes. Friend of mind tells me that he has been
in the shop several times with expenses up to $1500 and nobody seems to
be able  figure it out. What to look at next, considering there is plenty of freon
in the system?? Thanks for the help