Fire it Up....CLUNK

[Bad340fish]

I noticed this the other day, its more reacuring(sp) now. When I first fire the truck up in the afternoon it fires as normal and then I get a NASTY CLUNK and then all is good. It seems to do this when the AC is on, hell haven't had it not on in awhile. I don't drive the truck everyday. And it only does it when its first fired up, not anymore until the next day or whenever it gets driven. This happen to anyone before? It sounds horrible. All seems to be in check under the hood. I have to take it to the dealer anyways to have my LSD worked on. And I knocked it out of alignment on these wonderful tulsa roads the other day. TIA



PS Alignment under 3/36 warranty?

Clark

 

[TxDieselKid]

bad but good....

I too have this happen. I just got the truck 4 weeks ago, and have olny heard it about 5 times. It does seem to be something with the AC. I was just going to post something on this, but read yours. Someone please help us.



AJB

 

[mbrolin]

Its better to turn the a/c off before shutting down and then turning it on again once started. IMHO. The a/c clutch is engaged electronically when the key is turned on. The a/c pump is under pressure . The clunk is the clutch engaging and turning the pump against this pressure. No the alignment is not covered under warranty.

 

[HDH]

I also Have had this happen. several times!

It scared the crap out of me the first time this happened.

I thought a Cat was sleeping in the fan shroud and got chopped up in the fan!

I think its a Design flaw in the programing of one of the computers.

Doug.

 

[Shooter]

Repeat after me: THE DEALERS ALIGNMENT RACK IS NOT MY FRIEND -- good now again: THE DEALERS ALIGNMENT RACK IS NOT MY FRIEND -- good! now 20 more times.

You will be better off having it done by a good truck shop not a car shop like the dealer. the dealer will only put it in factory specs so broad that they are no spec's at all, not make it right by aligning it to any specific numbers or values.





The clunk is the ac compressor clutch engaging. Sounds bad; is probably bad; but no fix.



Michael: It still does it if you turn off ac before shutdown and turn it back on after engine has run a short while next day. I shut off the ac for faster cooldowns before shut down.

 

[Bad340fish]

It doesn't make that noise any other time. ONLY when starting the truck up. The AC clutch should disengage when the ign switch goes to the start position, just like your radio and alot of accesories cut off.



There is a very good dealer here. They have aligned vehicles for my dad many times over the years. I trust taking it to them.



If I can get a whole day off of work I will take my truck to where I went to school and do it myself. Even did some Training from Hunter Engineering. Haven;t touched an alignment machine since lol. Saying that I hope my teacher will let me lol. Thanks for the replies

Clark

 

[TXVINCENT]

My 99 has been doing this same thing since it was 6 months old. Mine only does it when I first turn on the A/C after starting the truck, I have always turned the A/C off before shutting the truck down. IT has seemed to be getting louder here lately. I always figured it was the A/C clutch engaging. Mine is out of warranty and has been for a while. Has anyone had this repaired or fixed it.

 

[Whitmore]

I think Michael Brolin has got it right, I would like to add my thoughts as this very insodend happens to me as well, I think that when you shut down the truck with the ac on and then let it sit the refridgerant condences in the system as the motor cools off then when you fire up the all mighty cummins the compressor has a small shot of liquids that it has to run thru it , I am sure this is not good on them either, what I do when I remember is shut the ac off atleast 2 minutes before the motor and I havent had the problem since ... ... ... it works for me Kevin

 

[OILBRNR]

The clutch does not engage for several seconds after the engine fires. Actually, I think it comes on the same time the PCM brings your guages to life.

 

[Ethdee]

You know, that might be happening to mine, too. I've noticed a pop or clunk twice now, but I assumed it was the vent doors sticking and popping open. My hearing isn't the best...



I wonder how many more there are?



Ethdee

 

[fest3er]

Originally posted by Ethdee

... I wonder how many more there are?

Happens to me, too. Sometimes I think it's the recirc door sticking.



An experiment: Try leaving the A/C on Max before shutting down, and see if the clunk happens. Try this a few times. Then leave the A/C in a normal position before shutting down and see if the clunk occurs. Try it a few times. This next one's a pain. Disconnect the vacuum to the A/C controls (plugging it, of course) and see if the clunk occurs.



If the clunk happens regardless of door position or vacuum available, then it's most likely in the compressor. If it *is* the compressor, likely the clutch is sticking and needs a bit of lube. How to lube it, I don't know!



Fest3er

 

[Bad340fish]

Not the Vents

I know its not the vents!! It was loud enough the first time it happened that I looked under the truck to make sure nothing fell off!

Clark

 

[Shooter]

Re: Not the Vents

Originally posted by Bad340fish

I know its not the vents!! Its loud enough the first time it did that I looked under the truck to make sure nothing fell off!

Clark

What he said ^^^^^^^^

 

[super38]

The clunk you are refering to is the fresh air damper slamming shut as vacuum comes up after the engine starts.





jd

 

[MCummings]

Here is a previous post about the same subject.



Harsh A/C Engagement





MerrickNJr

 

[WOWZY]

I have it too but not very often. I did see it happen after I started my truck one morning and got out to shut the hood. I heard a little "Pre-Clunk" and looked at the A/C, then I heard the loud clunk while I was watching.



What it looked like was the A/C clutch tried to pull in and it couldn't pull in all the way like if it had teeth that wouldn't line up at first. The clunk is really loud if you've got your head under the hood. It scared the hell outa me even though I watched it happen.



Mine only does it about once a month.