1999 VNL610 Cummins M11
I’m getting little to no air through my HVAC dash vents, floor or defrost. Does not matter if it's a/c or heat. This seems to have happened gradually overtime.
What I’ve done so far with little to no improvement:
Removed fresh air cabin filter housing, cleaned that intake area (drain was plugged).
Also verified the fresh air door is working via cab controls (closed, partial, full open).
Can see thru the fresh door firewall opening all the way thru the a/c coil in cab, so it’s clear.
Replaced “Fresh Air Cabin Filter” at firewall.
Heater core is clear, can see thru it with upper diverter ducts removed, so externally the heater core is clear.
Replaced blower motor. (Old one was working. New one appears to spin just as fast old one did.)
Verified no duct blockage. I removed the individual ducts from the top of the air distribution. Put the shop vac hose blowing thru each duct (dash vents, floor, defrost), each was getting plenty of air volume.
Believe I have verified that HVAC control that operates where to send the air is working. I can see that the 3 individual duct dampers work via the control lever.
Operating the blower speed switch. I can hear the speed change from 1 to 2 from 2 to 3 and no noticeable difference between 3 to 4.
Any thoughts on what else to try?
At this point I’m leaning towards replacing the blower resistor.