Weird noise coming from near the heater core

[rusty79beast]

I recently bought a 1994 Chevrolet Silverado Extended Cab 4x4 with 5.7L TBI and automatic transmission. A weird noise has come from the heater core area. It happens for about 15 seconds when I turn the ignition on or to run, and also happens for another 15 seconds or so when I turn the ignition off. It is a clicking noise, and at first I thought it was the fan hitting the shroud since it is located right near the heater core. Upon further investigation, I ruled that possibility out. Does anybody have any clue what is going on? This started happening right after I recharged the A/C with some more R134a. It might be a coincidence, but who knows. Since it does this only when the key is turned on or off, I'm thinking it's something electrical. If anybody has any ideas, please let me know, because I'm stumped.

Thanks a bunch

 

[rusty79beast]

Anybody have a clue???

 

[4xcrazy]

yeah, it's some sort of door motor or something in there,,,it's tapping noise right??? mine is doing the same thing, tried to tear into it one day, too much work, someday it will go to a shop.

Allan, (justhorsinaround) used to have one do this too i think.

 

[diesel4me]

yup--

I heard a caller on "Click and Clack's Car Talk" show with the same dilema--he even held his cell phone up to the dash so they could hear it!...they reached the same conclusion,a door closing on the heater/defroster --guy said it was a vacuum looking device with wires on it making the clicking..might be a link to that on "Car Talk"'s website..

 

[bear76]

It's the recirculate/fresh air flap. There is a wire/hose you can disconect, but it will be forever stuck in what ever position it was in when disconected. It wont hurt the truck in anyway that I'm aware if you leave it, mine has done it for about 2yrs. Check on www.fullsizechevys.com there is alot of info on this.

 

[rusty79beast]

Thanks for all the replies guys! I will check it out when I get up north to the hunting cabin in a couple of weeks.