After seasons of doing water flushes with less than marginal success, I finally got the guts up to try CLR. I figured it would either fix it, do nothing, or destroy the core. Anything is a good alternative to disassembling the dash.
So, this morning on the way to work, I cranked the heat and held my hand to the dash vents. Within a minute, it was uncomfortable to keep my hand there. Think I got it. I'll keep you posted.
Here's what I did. I got a long piece of heater hose and cut about 2 1/2 feet from the end. I attached this to the inlet and the remainder, which was about 5 feet, to the outlet. I then pumped water through the core to get out any coolant. Not sure that this was necessary, but I figured water would only dilute the CLR and I wasn't sure what coolant would do. I then sucked out as much water as possible with a wet-dry vac. The shorter hose, being previously coiled, stood straight up on the end. I coiled the other around the hood strut like a snake. I then poured in as much CLR as would fit. The whole bottle won't go in right away, but the level eventually drops as it begins working. I then did a process I call oral pulsation. I sucked in a little on the longer tube to draw the fluid in and then let it go back and then in again. I repeated this for about three minutes every 20 minutes. BIG WORD OF CAUTION. DON'T GET TOO ENTHUSIASTIC. CLR HAS AN ODD LEMON LIME TASTE, BUT STINGS. PRETTY SURE IT'S POISONOUS TOO. Take it easy on the suction and keep a big jug of water nearby just in case. I kept the CLR in for an hour and then sucked it out with a wet-dry vac. It will foam like crazy. Once I had the CLR out (and my vac was full), I continued with a water flush in both directions. I think switching flow directions frequently is the most important part. I flushed for a half hour which gave me plenty of time to clean the leaves out of the bulkhead with the overflow.