Hi Folks,
I just bought a 2005 F-150 Screw FX-4,and I have a loud "THONK"
Only 1 thonk at cold start,and it won't repeat the noise until it has
sat for a few hours.
My dealer said it was the A/C and was normal.I have never heard an
A/C that loud.Sort of sounds like the exhaust hit the frame rail,But
there is nothing even close.
Any help or clues to look for would be appreciated!
Thanks for your help!!
Clayshooter

 

Are you sure it isn't the blend door of the heating/AC closing/opening. This is controled by vacuum. I have heard this on more than one of my trucks.
Makes a nice little thump.

 

It sounds more like it comes from the engine bay,and it is quite loud,like a thump from a aluminum bat to the frame. Can't pin it down just yet.I have never had a noise from the A/C be this loud.

 

Yes on mine it sounded like it was coming from the passenger side front. Fairly loud. Not sure without hearing it, but with mine it was a thump, not a bang or any other type of noise.

 

Thanks for the response!
This noise sounds as though it comes from the drivers side,and from the rear of the engine area.Its just to loud to be A/C,as the dealer suggested.He reasoned that the compressor oil drains and has to refill and thus makes this thonk,and they say it is normal and no need to worry!
Famous last words,just before something breaks.

 

I bet it is the blend door. Try starting with the A/C off and see if it happens. They make a nice thonk.

 

My '05 screw does it also clayshooter. It only does it if it sits for 2 days or more, overnight startup doesn't give the noise. My guess is these new trucks start so quickly (about two revolutions on starter) that it is bearing rattle. I guess the oil drains out of the bearings etc and it starts so quickly that the pump cant fill it that fast. Who knows...it doesnt seem to hurt anything so we will see.

 

Question - what was the OLD startup noise?

Mine was found to be two beer cans rolling around under the seat

I did have one loud 'Thonk' every time, just before startup. This was traced to the driver's door closing. Hey - it was early!

A/C clutch? Try disconnecting the connector at the clutch. Mine is kinda loud on startup.

Cheers
Grog

 

It does it even with the A/C and all venting controls off.I'm willing to go along with the wait and see.It only has 600 miles on it,so warranty is still in tact!
Thanks for all your responses!

 

Hi Clay - the PCM commands the A/C compressor to run on startup, I think - for seal lubrication purposes - even if the system is turned off.

I know this because on mine, as part of my e-fan system I have indicators for things like the clutch engagement ( which turns on a second fan). That dang light comes on ( and a thonk is heard) on startup even with the a/c & ventilation system off.

Pulling the plug will check for that for sure.

Cheers
Vic

 

Sounds like it would at least put it out of my mind.
Thanks for the suggestion! I will give it a try tonight!