Thats not it, mine did it with no vacuum hooked up.

 

I also don't think it's the vents closing, it's a much louder, more prounced thunk than that would sound like IMO.

 

Unless my truck's got vents the size of 747 tail flaps, that ain't it, the whole truck shakes when I turn the AC on.

 

On mine at least, the clunk feels like its coming up thru the floorboards for some reason.

 

Maybe you guys are talking about something else. I can certainly feel it, but I wouldn't say my entire truck shakes. I just can't think of what else it could be considering the area where it seems to be coming from. I dunno.

 

Mine the whole truck does not shake, but a solid clunk can definitely be heard, almost like someone hitting the side of your truck with an orange or tennis ball.

Grr, dont ask me how I know what an orange hitting the side of the truck sounds like. I had my truck a week, still smelling and looking new, and some punk kids in my neighborhood were pelting every vehicle that went by with oranges(they hid in bushes and it was dark) Man was I mad, but no damage

 

Keep in mind that with the lower redline of the diesel, compared to a gas truck, the "gearing" for the compressor is likley very different. And the compressor is turning faster at idle in our trucks than a gas truck. Larger speed difference from off to on, big thud...that's what I'm telling myself at least.

 

steven, I think your absolutly right , I work in the HVAC field, and can tell you this noise is the A/C compressor kicking in at a high rate of speed.

 

My 2003 does it too. It definately on my vehicle is coming from the the compressor when first turned on for the day. The electromagnets in the compressor clutch really slam together. It makes my truck shutter. I've spoke with the dealer about it and of course says it is normal, "strong compressor". Someone mentioned different head pressures might be causing it first thing in the morning. That explanation sounds correct because no other time in the day is it as severe. It may be a strong compressor but I wonder what form of fatigue is taking place from that strong form of clutch engagement.

 

md11 - I can only say my tahoe did it the exact same way, and at about 90k miles the compressor failed and had to be replaced. Thats why the noise concerns me.

 

I know on my Hemi it sounded like someone was being slapped when the compressor would kick in, and it would go on, go, off, slap everytime. I don't think it's anything to worry about. It happens maybe once when I first start it with the A/C on. But, if the A/C is not on when I start it and then I hit the A/C button, it is very quiet . I don't worry about it. My friend has a Furd and his does the same thing.

 

On my '03, '01.5, '98, and '95 it's the fresh air recirculating door in the evaporator housing closing after sitting for a while. Yes it's loud. There's a lot of dash there for the noise to amplify through. It doesn't shake the truck so hard the tailgate falls down but it does sound like someone kicks the firewall. Ok by me. Try leaving the a/c on a fresh air setting when you shut it off for a while and see if it makes a difference when you fire it back up.

 

Same thing.

Pretty loud.

Usually happens first time each day.

Glad to hear it's "normal." Guess I won't worry about it.

 

It may be 'normal' and a problem....lol wouldn't be the first time..

 

add me to the list as well...every morning i cringe at the thought of turning the A/C on because i am afraid i am hurting my baby...and only 2k on the clock too