Harmon PF100 blower wont work with Plenum switch in automtic

Hello,

Forgive me for my lack of complete details. I've been called to active duty with hurricane sand recovery since the 26th of October. My girlfriend at home is having trouble with my PF100 and this is what I can tell....

The limit switch thats in the plenum, 11 inches above the top of the furnace, when set to automatic, the blower isnt kicking on. I came home briefly for four hours one night (after four hours driving) and briefly looked at it, switched it from auto to manual and back to auto and it ran for a few hours until I left. Today it aparently wasnt running again.

Girlfriend says she switches it to automatic and it shuts off before she can get up the stairs. Thermostat is set to 70 degrees, its 57 degrees in the house.

I know it generally needs a cleaning... but I gave it a total cleaning before I left too. Any idea what would cause this? From the trouble shooting manual, it appears that cleaning can be an issue. I cleaned it before I left and in november when I was given a day off... Thanksgiviing I think. I've only had 4 days off since October 26th.

Any thoughts?

Is the upper plenum hot to the touch when the blower kicks off?

TS

Its warm, as in you can tell hot air passes through, but its by no means hot.