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1982-2000 C/K Truck & SUV Chassis & Drivetrain Discussion Forum for the 1982-2000 GM Pickup Trucks and SUVs, and their Transmissions & Drivetrains, cab, chassis, electrical systems and a lot more.

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  #1  
Old 09-06-2019, 08:03 AM
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arveetek arveetek is offline
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Default No air out of vents on A/C

I'm having an issue with my 1995 Tahoe. I have very little air coming out of the vents on the dash. I've never thought there was proper air flow out of the vents, but this past week it suddenly got worse. With the blower on high, there is very little air coming out of the dash vents.

Here's what I know:

1. The blower is functioning properly. New blower and wheel in the past year. Works on all speeds.
2. The mode door is functioning properly. I can watch the actuator move from floor, to vents, to defrost. I seem to have more (normal?) air flow on the floor and the defrost, just not the vents.
3. The blend door is functioning properly. I can change the temp from cold to hot, and it appears to work as normal.
4. The recirculation door is not functioning properly. It broke a few years ago, however I have it propped up in the recirc position.
5. A/C is working. I have cold air, just not air flow out of the dash vents.

So what else could cause a blockage or restriction in the dash vents ductwork?

Thanks!

Casey
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1995 K1500 Tahoe 2 door, 6.5LTD, NP241, 4L80E, 3.42's, 285/75R16 BFG K02's; Kennedy OPS harness, gauges, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, Turbo Master, 3.5" Kennedy exhaust, F code intake, '97 air box; dual t/stats, HO water pump, Champion radiator; Racor fuel filter; 352K miles and running strong!
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Old 09-06-2019, 09:30 AM
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DmaxMaverick DmaxMaverick is offline
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Possibly a misaligned duct connection behind the dash. They are foam-wrapped inserts. The foam can deteriorate or unglue and go missing (usually causing a restriction), allowing the ducts to get out of place. If the fan is blowing, the air is going somewhere. Also, moving bellcranks doesn't necessarily mean moving doors, or fully moving doors.
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Old 09-06-2019, 12:10 PM
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To what Greg mentioned... See if you can reach up into the area where the dash vents are, and feel whether there is a lot of air blowing around in that area. If so, the vent ducting may have become disconnected/dislodged. It could be that some prior work (even before you got it) was the beginning of this problem.

You can remove the instrument panel and glove box/liner to see more into that area.
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Old 09-06-2019, 12:15 PM
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Ah, there are more linkages and flaps that I was not aware of. Skip to 11:05 for a good shot of the linkage and mode doors in this video:

https://www.youtube.com/watch?v=N3pG4EzSlko

I can visibly see the actuator and at least one arm moving. I'll have to get back under there to check the other arm that I didn't know was there. That's got to be my issue. Hopefully I can address what I need to without dismantling the entire dash.

Casey
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1995 K1500 Tahoe 2 door, 6.5LTD, NP241, 4L80E, 3.42's, 285/75R16 BFG K02's; Kennedy OPS harness, gauges, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, Turbo Master, 3.5" Kennedy exhaust, F code intake, '97 air box; dual t/stats, HO water pump, Champion radiator; Racor fuel filter; 352K miles and running strong!
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Old 09-07-2019, 04:49 PM
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Default Problem Solved!

Turns out there are actually 3 mode doors / flaps in the HVAC system, all of them controlled by one electric actuator. It's pretty neat how one electric motor can move all three flaps at different times. However, after careful visual inspection, it appeared that all three flaps were moving correctly. I could not see inside the HVAC box to actually see the doors, but everything seemed normal from the outside. I would have to disassemble the entire HVAC system to get to the mode doors.

I decided to remove the fan motor to check the cleanliness of the evaporator coil (I cleaned it a few years ago). Lo and behold, I discovered the evaporator was about 1/2 clogged with debris. The past 2 weeks at work, the feed mill directly behind our dealership has been drying corn, resulting in a ton of corn husk chaff to be blown all over our parking lot and vehicles. It's almost like brown snow. Apparently my rig has been sucking that chaff into the HVAC system where it got blown up against the evaporator coil. I washed it all out with a garden hose, and now the air flow is back to normal. What I thought was just reduced air flow from the vents was actually reduced air flow across the entire system.

Casey
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1995 K1500 Tahoe 2 door, 6.5LTD, NP241, 4L80E, 3.42's, 285/75R16 BFG K02's; Kennedy OPS harness, gauges, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, Turbo Master, 3.5" Kennedy exhaust, F code intake, '97 air box; dual t/stats, HO water pump, Champion radiator; Racor fuel filter; 352K miles and running strong!
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Old 09-07-2019, 06:37 PM
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Yep, that'll do it. I have 2 vehicles waiting for cabin air filter replacements, now (the evap's and ducts get a good blowing while I'm in there, too). I usually wait until the end of the dry season, but the reduced airflow we are now noticing will require it sooner. It's been a year of very heavy pollen, and too hot for me to find the gumption to do it. It's cooling off, so under the dashes I go this week.
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Old 09-09-2019, 06:31 AM
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I wish the older vehicles had cabin air filters...

Casey
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1995 K1500 Tahoe 2 door, 6.5LTD, NP241, 4L80E, 3.42's, 285/75R16 BFG K02's; Kennedy OPS harness, gauges, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, Turbo Master, 3.5" Kennedy exhaust, F code intake, '97 air box; dual t/stats, HO water pump, Champion radiator; Racor fuel filter; 352K miles and running strong!
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