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Little to NO HVAC air movement (1999 VNL610 Cummins M11)


CHIEFWAHO
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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.

275234234_5616981464982154_9981431194296

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Having completely rebuilt my virtually identical system, I think you're definitely on the right track with everything you've done so far. (I also have a 1999 VNL 610) The one thing you might be missing is the sealing of the individual duct sections. When I had mine all apart, I could see all the foam weather stripping was completely worn away. I ordered some pricey weather stripping and redid all the ductwork. It made a seriously dramatic difference. Seems like most of the cooled or heated air was leaking out long before it arrived at the various vents. You might check that out. It's definitely a chore to do, but well worth the effort. Good luck! Jay

Edited by Jaydrvr
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13 minutes ago, rickeieio said:

Unlikely, but possibly the blower is running backwards?  Wires switched?  I've heard of it happening......

Not sure that could happen, unless you cut off the connectors and hard wire it?? But then, we've all seen some butchered rat's nest of wiring, soooo.... Jay

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Likely not relevant, as I own a 2006 780.

I found my dash ac switch assembly to be the problem. I can switch the fan knob through each step, and hear the week sounding fan change speed.

I can also move the knob slowly BETWEEN each speed setting, and stop when the fan is going full beans. I stop BETWEEN the notches.

I know I could order a new switch assembly, but I am a cheap b@$+ฯ@ГΩ.

I can always find the sweet spot in between by fiddling with the knob.

Edited by Parrformance
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On 3/8/2022 at 10:40 AM, CHIEFWAHO said:

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.

275234234_5616981464982154_9981431194296

Oops. 
yes I would try the resistor. If the switch was not changing the fan speeds it is most likely corroded. I’ve replaced those before and some of them crumbled when removed. 
I may be checking mine soon because there doesn’t seem to be a lot of change in speed with my switch positions.

hopefully you’ll get it soon.

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