when i run my air it comes to defrost and/or floor no vents..I followed the line to the engine compartment and chased it to a round canister, then down to the tranny. By the way my 96 blazer LS doen't take off real good either could vacuum be the prob??

 

If you do a search about the vent thing on here, its a safety thing GM did. It defaults to defrost/floor so you can keep your windshield clear and have some heat on the floor. Im not sure about the tranny issue. Could be something else. But Im not for sure. I dont think the transmission uses a vacuum to operate but I could be wrong.

 

Almost for sure a vacuum issue. I'm not sure on a '96 but you make have that vacuum ball (accumulator) under the hood that's plumbed into the brake booster. Check all the lines for cracks, breaks & connections are secure.

As for the trans check the fluid as per the manual, I believe it's Hot, in Neutral & level surface.
How many miles since a fluid/filter change in it? Every 50,000 miles is what they ask for.

 

Almost always a vacuum issue; could be as simple as a cracked vacuum line. In my experience, though, visual inspection of the lines isn't as effective as getting a MityVac (or similar) and testing each line individually. Some of those holes or cracks aren't easy to see.

I assume you have 4WD; if so, I would check the transfer case fluid level. The vacuum line that goes towards your tranny actually connects to a vacuum switch on the transfer case, which allows vacuum to pass through when shifting into 4WD. The vacuum then goes to an actuator (under the battery tray) that pulls a cable that locks the front hubs. The seals in the vacuum switch are prone to leaking, which puts negative pressure inside the transfer case. The negative pressure will suck transmission fluid past the input seal and pull fluid into the transfer case. Over time, the transmission fluid level will drop, which could be causing your transmission problems.

I had this happen on my '96 Sonoma. Lost control of my vents around the same time my tranny got so it didn't like to move in reverse when the fluid was cold. When I pulled out the transfer case fill bolt, about 2 quarts of tranny fluid poured out. Also had to remove all the tranny fluid that got sucked up into the vacuum lines. All was well when I did that and changed the tranny fluid. But that all really did...suck.