Heater issue

Guys - The slider on my dash is stuck on the hot side.  I followed the cable to the heater box on the passenger side firewall and tried to manually move the rod the cable is connected to, but it 'thunks' against something inside and can't be moved.  I'm afraid the only solution to this is going to be to remove the plastic cover to the core & motor to fix it.  Should I drain the coolant before starting or can I leave the hoses connected to the core and open this up?
I used my truck the other day in near 90º weather and could feel ambient hot air (no fan going) giving me something else to do to the old girl.

Is it possible that the cable has slipped in the outside clamp and the door is already almost in the closed position?  I would take the clamp loose and the cable off the door to see if the door can move in its full sweep w/o the cable.

But you can take the inside cover off w/o removing the heater hoses or draining the coolant.  All you are going to do is get to the inside of the heater core.  But you might be able to see or feel what's keeping the door from moving.

I second Gary's test.
Did it work recently? If the door won't move without the cable, maybe something like a dirt dauber's nest inside there

Thank you, Guys!  I removed the cable from the arm and it swings fine.  So, something is coming in contact with the lever behind the dash and I'm going to have to remove the dash cover and radio to get to it.  Ugh!
Thanks again for the help on where to start!

Dumb question, but it moves freely without the cable but won't with the cable connected, wouldn't the issue be with the cable?

Not a dumb question at all. At this point looks like Tom is left with the lever itself being hung up which could be a connector that fell into it preventing movement OR it could be that the cable is bound up by dust or rust.

Will be interesting to see what it turns out being.

might even find that small wrench thats been missing since the radio got put in

You're not far off, Mat!  I'd made a bracket for the back of the radio to hold it tight.  As soon as I took off the top of the dash and loosened the radio, the heater cable worked beautifully.  I made another bracket and fixed it to a screw hole in the unused, empty central speaker location.

Chalk this up to moronic shade-tree fixes.

well i guess we all learned something today. silver linings man! silver linings.

that made me think of an old story. years ago i used a regular mechanic . time was at a premium and i made more then. i took my wifes pontiac in for a noise. i explained it to him as " imagine the sound of a 7/16"great neck combination wrench bouncing around on the upper portion of a lower control arm when hitting a bump" well it sounds like that. he just looked and grinned saying that was oddly specific. anyway he was able to fix it , all good!

Happy you found the trouble!


Reading at you, this vaguely reminds me of something similar, I had with this heater cable.  Too far in the pat to be clear, but I remember that the trouble came from something else than the cable or the flap.