My 1997 Chevy blazer will hardly blow any heat, when you turn the cold air on the air flow is much stronger. But when I turn it to heat the air flow drops way off and also even when my truck warms up the heat never gets very warm, It's definitely there but just doesn't get very warm. Could this be the heater core? Or is it more likely something else?

 

Whatever you do don't buy a heater core yet. My Jimmy and Blazer both had this problem. Go to the hardware store and get some clear plastic tubing. I believe the heater core inlets are 2 different sizes. 3/4 and 5/8. Get a foot of each. Also get a garden hose end to put on the hose that you're going to connect to the HC outlet. disconnect both heater hoses. Connect the clear hoses and clamp the hose that connects to the outlet. hook up your garden hose and carefully back flush the HC. Watch the other clear hose to see all the crud that comes out. Once you start getting it cleared out you can turn up the water pressure more. A friend of mine also did this on his bravada and it heats like new. And change your thermostat.

 

Make sure to check your gauge first, if the engine is not coming up to operating temp, it is more than likely the thermostat stuck open (safe mode). If this is the case simple replace the thermostat.