Thumping in cooling system

[cdxhizors]

Should I just replace the heater core? I hate to throw parts at it but idk what to do. This is getting annoying.

 

[jeremysdad]

Possible issue with bypass valve/vacuum line? Take it out and run the hoses straight to the core and see if it stops. AC runs when you're in defrost. Just a thought.

 

[cdxhizors]

Possible issue with bypass valve/vacuum line? Take it out and run the hoses straight to the core and see if it stops. AC runs when you're in defrost. Just a thought.

I appreciate the input.. A/c doesn't work.. No lines or condenser lol so I've ruled that out.

I'll try brass fittings to bypass that valve. I've already replaced the valve and confirmed that it has vacuum.