Running air conditioner cause error light to turn off

Have an error code appearing that says I
need to replace my egr valve, so I did (a very
qualified mechanic did it).  Now the code
cane back.on saying egr needs to.be
replaced. Was told it might be a computer
issue.  I have found that when I run the air
conditioner, it makes the error code resets
and goes away (light turns off). Is this still a
computer issue?  Still not sure what
computer issue it would be and was told.its
a.dealer only repair.