Chrysler Repair: Heater Blowing Cold/ Wont Shut off, drb iii, double failure

Question
Hi Roland,It made me start a new question.
The relay is not the problem. I swapped it out and it still kept blowing after I powered the unit down.
What next?
Auburn

Answer
Hi Auburn,
I suspect the blower motor module is your problem. I will copy and mail the pages about changing that to you. If it is very expensive you might want to check with the dealer to see the cost of using the diagnostic reader to see what is says it sees as the problem. It would take a double failure of the control panel (energizing the relay* and failure of the speed control function) to cause the blower to run on high continuously.  That is not out of the question, so a readout might be worth it, particularly if you made a gentleman's agreement to buy the power module if that was so-indicated by the DRB III (so that they might not charge you for the readout?). You might want to look for a used control panel if that turns out to be the problem in light of that price, so don't agree to do that for a free readout :)
Roland
*it is not explained in the manual as to whether the blower motor relay is energized all the time the ignition is on or if you also have to have the control panel at 'power', so that may not be a 'failure' mode at all. But I still suspect the power module for the blower motor because it evidentally generates a lot of heat and that means it is subject to failure if it is not kept cool when the blower is running. That is why it is placed in an intake air duct of the system. That sort of solid state device is prone to failure if not cooled. If for example the air intake was ever blocked by leaves, the blower module could have overheated.