1997 Jeep Grand Cherokee Heat Function Selector Problem

Hi Jeepies,
I suddenly have a situation where the heat selector control is stuck on defrost. Doesn't matter where you move the knob, you get defrost.
Can anyone tell me what controls this? Electric? Vacuum?
I can't get a bead on troubleshooting online, but I do get 50 ads for places trying to sell me a blend door repair kit...

Thanks!

http://www.ebay.com/itm/142229095598/www.ebay.com/ (http://www.automotiveforums.com/vbulletin/www.ebay.com/)
I would start pulling this item first check for vacuum. If you have vacuum make sure rotary switch works. Then check electrical switches and check for power to unit. I've had the vacuum connection plug at intake manifold before.
For broken plastic vacuum hose. I use a piece of vacuum hose about 2 inches long. I push the plastic tubing until it stops on each side. It make break somewhere else but the hose lasted until I sold the vehicle.

I started poking around the firewall and found a small cracked rubber hose that splits off from the main and goes through the firewall at about the right place for a vac hose to go to a heat selector box. Upon further inspection, it turned to dust in my hand so... I don't reall know how far it goes through the hole in the firewall to the connection, I don't know if I'm going to have to do an interior tear down to resect a new piece of hose from manifold to control box.
The fun never ends...

The hose is fairly cheap but labor intensive.

I guess that's my next question. How much tear down is involved in replacing that hose on the controller side? Is the whole dash going to have to come off to get to it? Seems like I could see into the hole it went into, through the firewall, if I could stand on my head...

I would pull the control as pictured in the link I provided. Find the rotary vacuum switch. Identify the supply vacuum hose. If you can't find where it comes through the firewall bore a hole bigger than the hose find a rubber grommet insert it and run a new hose through the grommet hook it up test. If working properly caulk the opening through the firewall. I've run a new wire this way. It lasted until I sold the vehicle.