Strange occurrence. While winterizing AC system today, went to run antifreeze through AC system as I usually do and couldn't get anything to flow through system. After several attempts, took hoses off pump and intake of coils, no blockage - could blow through very easily. So took hose off discharge of coils - same thing, flows freely. Put it all back together and hooked fresh water hose up the hose that attaches to discharge side of pump and tried again. Water went through and was quite brown when it came out the through hull. It eventually cleared up and I let it run for about 10 minutes and shut down. Ran to store to get a fitting and came back. Went to run antifreeze threw again and same issue. No flow, clogged. Did same thing, both hoses clear and coil is blocked. Just don't understand how blocked again after just a n hour before could run water through easily. Cannot get anything through coils now - water nor air. Anyone experienced this? Is there a way to unclog coils? Was considering Barnical Buster, but unless I can get it to the actual blockage, not sure it would work.