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Discussion Starter · #1 ·
I've been searching these forums for a while now, but I'm not sure I've got an answer. My problem is a loud CLACK-CLACK-CLACK that comes from behind the dashboard. It only happens when the A/C cuts in, like starting up on a warm day or when the sun hits the dashboard sensor. It sounds like an angry little person with a stick trying to get out. Usually it is three raps, but sometimes two or four. My original thought was that it was a solenoid misfiring due to a short circuit or something like that. The closest that I've been able to find in these forums is the mode door actuator failure, but descriptions of that don't seem to include the sound effects I'm getting. Also, there doesn't seem to be anything wrong with the actual functioning of the system. I guess I could ignore it, but I hate it when things aren't right. Has anyone experienced this (and hopefully figured out what it is)? The details: '02 Envoy SLT w. automatic climate control.
Thanks to all.
 

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2004 gmc
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Sure sounds like it. To confirm, pull the fuse HVAC-B #36 in the rear fuse block while the ignition is off. Then put the fuse back in, then turn the ignition on but don't start the engine, and don't touch any controls for 90 seconds. Listen for the actuators to cycle through their travel, plus the blower will operate if it's the automatic control system. (I don't have the manual system, so I don't know what happens for those folks with regards to the blower.)

A dealer's tech tool can address each of the actuators and confirm a guess diagnosis - but that might cost as much as replacing one and guessing wrong.

Anyway, you might take part of the dash out and listen more closely or touch them during the noise to see if you can discover the right one.
 

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2004 gmc envoy_sle_xl
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HVAC actuator issues

Yes, it's the actuator, the problem is trying to find the one that's acting up. You may have to try different blower directions to see if the problem goes away or stays there. I had that exact same problem with the rear heater controls. Ended up being the acuator that controls the face, and face/floor door.
One problem I am having with my front HVAC is that when you go to full heat, the flow through the vents drops almost right off. I am assuming the actuators (2) for heat are worn out and not closing right, cutting off some of the fan flow. If i move either side or both at the same time to full cold, the fan flow comes roaring back.
I would change both heater actuators, but they're a pain to get at and about $50 CAD each! Plus you gotta rip a lot of the dash out
 

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Discussion Starter · #4 ·
Interesting, I tried the Roadie's suggestion but didn't learn anything. Everything behaved itself OK. I guess I'll have to play around some more.
 
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