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Discussion Starter · #1 ·
Like the title says Its not the blend door actuators (Or I should say I would be very surprised) as the knocking noise happens even when I have both HVAC fuses pulled and the controls don't function. It doesn't start until about 10 minutes into driving and is then intermittent. I can feel the heater box and it certainly feels like the knocking noise is coming from there. When I have the fuses in and the key to the run position I can hear and feel all actuators working correctly.

I originally thought it was my passenger blend door as I unhooked all other actuators and it still knocked so I replaced it and I still have the knocking noise. Anyone who has replaced it knows what a huge pain that is.

I appreciate any advice.
 

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I used to have heat while the knocking was going on but now no heat and the same knocking sound at intervals of about every 10 seconds roughly. During the summer I flushed the coolant so I may have air lock or a blockage in the heater core or something, although I thought it would work itself out by now if that was the case but I only get luke warm air coming out when at operating temp.

I may need to flush my heater core but I'm open to other suggestions, especially in regards to what the knocking sound from the heater might be.

Sorry if this seems like I'm hi-jacking your post, it just sounded like the exact same problem I have going on with my truck. I'll see if I can get a video of it making the noise.
 

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Discussion Starter · #6 ·
No worries. I noticed today that when it would knock if I kept it above 2000rpm it would quit and then immediately come back once at idle. I tried burping the coolant today but it is still knocking. I'm about to take a sawsall to this thing.
 

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Well after replacing my thermostat and there is still barely any heat and the knocking is still there. Kind of sounds like it's coming from the water pump, would it be possible for the water pump to knock about every 5-10 seconds but only when my heater is on?

I also think the no heat problem may be a clogged heater core because 1 hose going in is significantly hotter then the other one going out. I may have 2 problems going on at once here.
 

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Ya that's my next plan. I don't want to take the connections off at the firewall because they are known to break.. So I was thinking about taking them off on the water pump side and attempting a flush from there. Just not sure which hose I want to connect the hose to in order to back flush the heater core.
 
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