I have been having a problem with the heat and defrost system in my truck for awhile. After I run the heat or defrost on warm for awhile I get this persistant noise/knock. Its repetitious and it seems rhythmic when it happens. It just repeatedly goes" boom boom boom" about 3-5 seconds spaced apart until I cut it off. As soon as I cut it off it goes away. I was talking to my grandad and he sugessted it could be air in the system? It def. Seems like its coming from the heatercore/firewall area as far as I can tell. I also seem to have a water leak problem that I have repeatedly looked for but I can't find in the passenger area of the cab but I don't think its related.

Any help is much appreciated.

 

Sounds like your heater core is leaking.

 

Unplug the clutch on the A/C compressor and see if that makes the noise disappear.
As for the leak , is it water or antifreeze ?

 

I def. Don't think the heater core is leaking because its not antifreeze that I'm finding. I'll try that with the a/c clutch.

 

Anyone else ever experienced this?

 

Take the radiator cap off with the truck cold. Let it idle 15 20 minutes with it off and the heat on high. Top it off if needed.

This will ensure there is no air in the system, if the noise goes away you had air. If it comes back you have a coolant leak.

 

that problem was the first question I asked when i joined the forum. I never got a proper answer. By the looks of it though, Blhde might have answered my problem. Gonna try that in the morning. Im quite sick of people asking why my rig, which has 60,000km's makes a knocking noise in park, with the heat on. Sweet baby jesus! Finally!

 

also could be the blend door actuator

 

wait wait wait...if it is the thumping from under the hood, hold one of the radiator hoses and see if it jumps when the thump happens...if so there is a fix TSB for it...PM me for info and prices

 

I just learned today that I think this may be the problem or the blower motor itself! I did the cap off idle and it didn't get rid of it. Does the blower motor itself control the blend door?

 

Is this a ranger thing?!

 

the blend door controls hot and cold not the blower motor....first feel the hoses as i mentioned...because you dont want to dig into the dash for no reason

 

Okay will do..i'll check the hoses tomorrow. Thanks for the help!!

 

Now I know my truck is old...Controls cold and hot.Hot is when you put the heater on ,cold is opening(ROLL DOWN ) the window. I am going to need a RANGER DICTIONARY. I thought you guys were yankin when I saw this Blend dour control. Oh I have to come back and keep reading....This place is like gettin addicted to Days of our lives at lunch hour as a teen.(Only one semester) got over it.