What could that be ?

[Swedishmoose]

Hi there,


I've got a question about a weird noise from behind the dashboard.

It is a Ford Falcon Futura 4 speed Auto ( model year 2000 ) with manual aircon.



Everytime I turn the aircon on it takes about 5 -15 seconds and than you can hear one knock from behind the dashboard. It is pretty loud and you can actually feel the the knock in your left foot when it is resting on the plastic foot rest.

I was thinking it could come from the heater or aircon element behind the dashboard.

Could that be a sticky air duct ( flap ) or something like that ?
But if that was the case it should always do it and not just when I turn the aircon on because all ducts and flaps are operated through vacuum lines.

Is there a valve or something that can get stuck ?


The only difference I have noticed was that it doesn't do it all the time when I first turn on the ventilation fan first ( without turning the air con on ), wait a bit and then turn on the aircon.


If I turn the aircon on right after starting the car it takes about 5-15 seconds...KNOCK...but everything seems to work allright.

I just want to avoid damage in the heater element because its no fun to take the whole dashboard out for crap like that.

Are there any cleaner or lubricants that I can spray into the ventilation system when I put the air distribution switch on recirculation ...like spraying it into the air intake on the passenger footwell side ?


Any ideas what it could be ?


Thank you for any info



cheers


The Moose