'97 C1500 - Clunk From Passenger Side Dash When Max AC or Recirc Are Engaged

[df2x4]

So my red '97 C1500 has developed an interesting issue. Whenever I engage Max AC or recirc, there is an audible "clunk" sound that seems to come from the lower passenger side dash every 25 seconds on the dot. Everything seems to work fine, I can hear the volume of airflow change whenever I engage either of the problematic settings like you would expect. Whenever the "clunk" occurs the airflow seems to diminish for a split second. The regularity of the sound makes me think this might not be a typical actuator motor failure, but admittedly I've never experienced anything like this before so I'm not quite sure what to expect.

My HVAC control unit is original to the truck, and one of the mounting tabs has been broken for nearly 10 years now so it flops around a little. That combined with the consistent interval between the noises (and the fact that the recirc door seems to work except the exact moment when the noise occurs) makes me think that maybe my control unit is to blame.

I'm open to any input on this. Guys who have had the recirc actuator motor fail, does this sound like what you experienced? I get no grinding noises or anything that sounds like gears, just a clunk every 25 seconds when Max AC or recirc are engaged.

 

[Z71Hobbs]

Might be a relay failing on top of the hvac box?

 

[df2x4]

Is that actuator controlled by a relay? I'm fairly confident that the noise is the recirc door making contact with one side of the box, as the volume varies a little each time.

@someotherguy, I just found your guide on ChevyTalk for replacing the recirc actuator motor in an '88-'94. Comparing parts diagrams for a '94 and a '97 side by side, it looks like the systems are a little different. Just curious, do my symptoms sound anything like what you experienced when your recirc actuator motor went bad? I'm finding a lot of posts from others saying that they would have 20-30 seconds of solid clicking or slow/nonexistent mode switching, I'm getting neither of those.

 

[someotherguy]

May be actuator, may be controls. They're the same basic setup but the controls do behave differently. I've experienced a few 95-up models with that continuous back and forth on an actuator but they weren't my vehicles to diagnose/repair. IMO the actuator is probably still the issue and it doesn't know its end position so the controls keep running it

Richard

 

[df2x4]

May be actuator, may be controls. They're the same basic setup but the controls do behave differently. I've experienced a few 95-up models with that continuous back and forth on an actuator but they weren't my vehicles to diagnose/repair. IMO the actuator is probably still the issue and it doesn't know its end position so the controls keep running it

Richard

Thanks for the info. I'm going to go ahead and order a new recirc actuator motor. I have a brand new control unit on the parts pile to throw in if the actuator doesn't fix it.

 

[delta_p]

if you take out the blower motor you can see the door good, or looking from underneath where the through the recirc intake. The door may have come off the notch on the opposite side of the actuator which can be fixed through the blower motor passage. It may be flopping and the actuator driving back again.

 

[df2x4]

if you take out the blower motor you can see the door good, or looking from underneath where the through the recirc intake. The door may have come off the notch on the opposite side of the actuator which can be fixed through the blower motor passage. It may be flopping and the actuator driving back again.

Thinking this probably isn't the case due to the sound of the airflow, everything seems to work fine except at the exact moment of the clunk. I will keep it in mind though, thanks for the heads up about accessing the door by removing the blower motor!