All but 3 vents blow cold air w/ AC on

I have the same problem with my '99 also. I checked the filters in the back of the glove box and they we in bad shape. All the vents got colder after I removed them but still the 3 left dash vents were not. There has to be a vacuum motor somewhere or the hvac control unit must be bad. If I find anything else out, I will post it here.

Thanks for the post and reply. That's interesting about the left 3 vents not working after taking the filters out. I agree...probably a vacuum motor or a diaphragm that either went south or a hose or two got disconnected. On a different car I used to have, that was a problem I encountered...the center vent diaphragm busted and I had to replace it. If you find out anymore, please post. Thanks again!

my 98 Venture was doing the same,, but when I added more refrigerant to the system,, we have COLD air from ALL the vents

We tried the same with ours, but it didn't do the trick. Turned out the compressor was bad. With my other car however, adding refrigerant did the trick. Definitely worth the $$ to try adding the R134 to see if the system needs a recharge first. Much easier and cost effective remedy to try before ripping out the compressor. Glad yours worked out with the additional R134.