HVAC Problem

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98chevy2500SS

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This issue is on my 97. When I turn on the Defrost+Floor vents w/ heat, after 15-20 minutes or so it will start blowing very weak until I switch it to Front Vent, wait for it to start blowing, then back over to the Defrost+Floor Vent and then it will go back to normal. I will usually move around the temp if it gets too hot and it might be a trigger for this weak blowing, but I don't know. This seemed to have just happened a few days ago when it started getting cold. The blower motor is working, I can hear it moving like normal. It doesn't seem to have a problem with the front vents, as it blows just fine. Is this something as simple as lubing up the actuator links? I will check the coolant to see if that's triggering it, but I do have hot heat, so I wouldn't think that it would be an issue.

Kinda weird why its acting up now, last fall it didn't do this, it stayed on the Defrost+Floor Vent the whole time I was in the truck in the winter, no issues.
 

someotherguy

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That does sound like typical gummed up link behavior. My 94 would do that and eventually go *thunk* as the linkage let go and the door slammed into position. Cleaning/lubing fixed jt.

Richard
 

98chevy2500SS

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Thanks for the reply. Lubed up the actuator, and also checked coolant this morning. All tested out good. Observed a little more on it this morning. When I have it on LO on the Defrost+Floor with heat, it will blow weak after 15-20 minutes. But when I switched it to cold this afternoon, and the Front vent mode, with fan speed on LO, it didn't blow weak after 15-20 minutes. So I am a bit confused why it acts up on the defrost+floor setting, it doesn't seem to do it to any of the other modes.
 

someotherguy

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I hate to suggest this since those controls are so fragile (especially the plastic tabs) but if you're up for it, it may be interesting to see if swapping controls between your 97 and 98 makes it behave. I haven't seen the vent position actuator go bad yet, but surely they can go bad just like the temperature mix (rare-ish) and fresh air/recirculate (all the time.)

Richard
 

95C1500

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I busted the mounting tabs on my controller years ago when I tried swapping in LEDs. I haven't brought myself to order another one off Amazon (the only place I've seen that has any in stock)
 

98chevy2500SS

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@someotherguy, I didn't even think of that. I could give it try. The guy said he put a brand new control unit in it not too long ago, or so I think. I could find a factory unit out of a junk yard sometime, but yeah I could swap the units tomorrow and see if it changes anything next week.

@95C1500 yeah I did the same thing on my 98 when I swapped in LEDs, until I figured out you have to press in the tabs instead of prying them. I only broke one though, sounds like you broke both, haha.
 

95C1500

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I pressed them and they both snapped. The face plate is literally "held" in place by the dash bezel lmao
 
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