I have an 04 ranger 4.0 the compressor was hanging up it was replaced, some kind of by pass hose was installed to the dryer, new orfice and tube, however when the temp is set at mid range deferoster turned on or air, at times more than fewer when the compressor kicks in there is a very loud thumping noise coming from the pass side firewall engine compartment area/ heater box area, also at higher speeds the truck jerks when compressor engages, sometime it engages you can hear the click from the clutch and no problem, warmer days when it calls for more air its does it a great bit,

 

I too, hear a "thump" when I turn on the HVAC system in my '04 Supercab. Maybe it's the vacuum system that moves from vent to floor to defrost, etc. It really makes me feel like I ahve a cheap truck.

 

Thanks, I checked myself on that its not the door in the heater box, what it is when the compressor engages with so much force its slams the hose into a round vaccum canister that is mounted on the inner fender well, How do I know this I got under neath the vehicle and watched it, however it didnot fix the problem, The compressor was hanging up also, so the dealership said they replaced it! They also put some kind of bypass line on the dryer "still thumps at times mostly when RPMs are increased around 1500, This also makes the truck jerk sortta like cutting back hp on the engine, I had the vehicle in six times for this and they agree its an issue and there is something wrong but cant fix it,I had them disconnect the air and Its runs fine no complaints,I am contacting Lemon Law people to get in touch with FORD keep in touch and give me more info Thanks! harry

 

I was told this morning that this problem could be a sensor, engaging the compressor too often, compressor is engaging too often when defrost is on,