My 1996 Blazer is misting up inside the cabin. This is obviously due to moisture in the heater/blower system. This is NOT a leaky core as there is no smell of anti freeze. There is however a mouldy smell similar to a curry smell. This tells me that water is collecting in the system somehow. Also the operation of the fan (blower motor) is intermittent, after a rainstorm it may not work for a day or 2.

My question is; Is there some kind of drain hole in the blower motor or vent system that is blocked? I guess this might be the case but I cannot see where?

 

Yes, there is a drain at the bottom of the HVAC case located directly in front of the firewall on the engine side. If you look at where the AC lines go in, there will be a 1" to 1.5" wide flat protruded area where the two halves of the case come together. If you follow this down to the bottom of the HVAC housing, where it meets the firewall, there will be a hole there. It is VERY difficult to see as it is directly above the frame and there is a ton of stuff in the way, but its there. To get good access to it, you may need to pull the passenger side inner fender. This is what I did to clear the drain on my housing.

The next thing that you should look for is leaves or other foreign material in the cowl of the truck that may be causing the water to feed into the HVAC housing.