Defroster Noise

[cbsmith]

I have a 2005 Sierra Crew Cab 4x4. When the front defroster is on I hear a clunking noise coming from behind the dash int he engine bay. I can hear it clearly when I am stopped, even with the radio on. I can also hear it when driving if I turn the radio down. It happens about once eveyr minute. It has done this since I bought the truck two weeks ago.

 

If I turn it to one of the vent positions and turn on the AC I hear the same clunk, but only once. I think it is the AC compressor engaging. Then I get cold air, so the AC seems to be working. I am just wondering if the AC is supposed to cycle like that when it is on defrost.

 

I guess I should take it to the dealer to be looked at, but thought I would ask here first.

 

Chris

[BBSilverado]

I have a 2005 Sierra Crew Cab 4x4.  When the front defroster is on I hear a clunking noise coming from behind the dash int he engine bay.  I can hear it clearly when I am stopped, even with the radio on.  I can also hear it when driving if I turn the radio down.  It happens about once eveyr minute.  It has done this since I bought the truck two weeks ago.

 

If I turn it to one of the vent positions and turn on the AC I hear the same clunk, but only once.  I think it is the AC compressor engaging.  Then I get cold air, so the AC seems to be working.  I am just wondering if the AC is supposed to cycle like that when it is on defrost.

 

I guess I should take it to the dealer to be looked at, but thought I would ask here first.

 

Chris

 

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The AC copmressor does cycle on and off when you use the defroster even when the AC is not on. It will cycle at different rates depending on the temp and engine RPM's, but the noise is not generally that noticeable.