Heat/air conditioning problem
 

I have a 2000 Blazer. The heat and air work great when they are working. It appears the controls randomly may not tell it what to do. The air will come and go. It is cold when it's working. Same with the heat. Any suggestions will be appreciated. Thanks!!!

Automatic or manual climate control? When you say they come and go, is it the fan that stops working or does the air get restricted/redirected by the HVAC system?

It is automatic and it seems the air gets redirected. Can this be a vacuum problem?

Possibly, but that typically leads to air being diverted to defrost and heat outlets, not an overall restriction. Sounds more like a door has broken inside the HVAC housing.