99 Sub. A/C Problems

I have a 1999 Suburban with front and rear A/C. When the A/C is on and I put the fan on med or high, I hear a suction sound and the air stops blowing thru the dash vents. I have to shut the A/C off and turn it back on to blow thru the vents. It doesn't do it on low. :banghead:
The rear A/C is not affected......
Any ideas?????
Thanks
Peter

Sounds like a bad controller. If you check through the past threads on this subject, you will be able to verify. I have seen similar problems posted here before.