Chevy not blowing cold air

I have a '96 Chevy Astro Van and the air conditioner was not blowing cold air. I found out it was a Freon gas leak problem. I took it to the Chevy dealer and they replaced the leaking suction discharge hose. Next day, I found out that the rear air conditioner was not blowing cold air. It was working fine before the Freon gas leak. Now, the front A/C works fine but the rear A/C is not blowing cold air. The blower motor is good, rear A/C switch and speed control works fine. What could be the problem?