1996 gmc 3500 cube van when heater fan is on and in cold position it blowes very hard but when you turn it to full heat it hardly blows at all?? what do I need to clean or fix
It sounds like there is something between the blower and the heater core, maybe even on the core itself. It could just be leaves which have gotten sucked in and are now blocking it. When the blend door is is over to the cold side, it blows air just fine. Yet when the blend door is pushing across the heater core, it is greatly reduced. This leads me to believe there is something plugging it. You'll need to tear the heater box on the inside apart to figure out what is blocking it. You might be able to do this by pulling the blower motor from inside the engine compartment. Once it's off, it should give you access into the area where the blend door is at (I believe). I suggest doing this first, because it is about a 10 minute operation to pull the motor. Here is a nice video of how to remove the blower motor. If you don't see anything there, you'll have to tear things apart under the dash on the passenger side. There should be the heater box accessible under the dash which, once pulled, should allow you to see if anything is in there blocking the blower.