This is kinda weird, so I think. Okay '99, 3.0 V6 5 speed.
I turn on the heater and switch the dial to defrost. And about every thirty seconds I hear a loud knock under the hood. Kinda like the click you'll hear when you're running the AC. Only more like a knock. When I switch the dial to feet only or to the face only position located between the "AC" and "OFF" position I don't hear it. All other directional positions I can hear it. Is it perhaps my AC condenser operating while the heater is switched on? I mean this "click" is so obvious I can feel it through my stick shift.
Now here's what I think it is. Air flow directional control mechanism is busted. Knocking is something that should stop but keeps turning and blah blah blah. I really don't know what the hell it is!
Wonder what the heck it is.

I have similar problems with my 4.0 wish i could tell you what is but i have no clue.

Well if I ever get time to check it out more closely I'll fill you in.

It is your AC compressor, probably rapidly approaching a violent death. That thunk is the compressor starting up when the magnetic clutch engages. Your feeling it in the driveline because the AC compressor is turned by the engine. Any drag exerted by the AC compressor will be felt in the driveline.

The AC runs in all positions except vent only and floor only. All the other settings run the AC which is why it doesn't happen when you have it on vent or floor. The AC does not care if you are using heat or cold air. It just does its thing regardless.

__________________
(Formerly)
FireRanger
2003 Edge 4.0 4wd

How to: Aux light wiring, relays, & fuses
Info: 300+ intake threads here on FRF
Info: HID Projectors
How To: NO HEAT Troubleshooting Guide

Disconnect your AC compressor in the winter time, thanks to Fords climate control, your AC comes on when the temp sensor in the cab says it is too warm now.

Ray

__________________
White 2002 Ranger XLT Extended Cab 4.0 4x4 4.10 LS
5 spd,/BW1354e
K&N CAI 77-2529KP
Jet Chip
2 1/4" Exhaust
Explorer Dome Light
IN THE WORKS:
Sable Electric Fan


“If you do not know where you are going, every road will get you nowhere.”
—Henry Kissinger

Oh great! @%&#!! What kind of a violent death can I expect? Will it cease up and fry the belt?

Oops! Almost forgot to thank you FierRanger. Thanks!

Gonna do it right now! Thanks

Try Clem's method! It cured mine. No more clunk and click.
But it looks like I will need a new AC here.

Disconnecting the AC compressor will keep you going for now. It isn't going to FIX it, but if it isn't in operation, it doesn't matter if its broken. However, just remember your defroster is like 75% less effective without the AC compressor in operation so just be prepared for fog that won't go away.

If I were to guess what will happen to it, it will probably just destroy itself rather that seizing and preventing the pulley from turning, but that's just a guess.

__________________
(Formerly)
FireRanger
2003 Edge 4.0 4wd

How to: Aux light wiring, relays, & fuses
Info: 300+ intake threads here on FRF
Info: HID Projectors
How To: NO HEAT Troubleshooting Guide

Over the years I have replaced countless starters, alternators, breaks, in tank gas pumps but never a AC unit myself. I guess it's time to tackle that now. I guess the first thing I need is a chilton's rangers manual.

They sell just the ac clutch at autozone i think its 85 dollars atleast thats what it is for mine. Im probably just going to fix it right get a new clutch put on. Im just wondering whats going to go on it next it seems like buying a ford vehicle newer than 1980 is a bad idea.