Chrysler Repair: Inadequate heat:: Is it the blend air door? 98 Van, plymouth grand voyager, calibration capability

Question
1998 Plymouth Grand Voyager, 3.3.  Water is circulating through the heater core.  Very little heat on floor but none on defrost and from dash.  Where is the blend door?  On previous post you say on bottom of unit.  Explain to me what the unit is.  The dial where you pick where the air comes out of moves very freely.  Will slide up and down when you hit a bump, but does work.  How do we fix this problem?  Is it something we can fix or does it need to go to a dealer?  Thank You.

Answer
Hi Dave,
The van heater/AC unit in the '98, according to the shop manual,is very much electronic in the controls and internal door actuators. It also has a self-diagnostic and self-calibration capability. The entire unit is described on 40 pages in the manual and the wiring diagrams are 8 pages.
There is a complete description of the calibration test procedure, as well as details about how to service some aspects of the unit without removing the entire distribution system which is under the dash, behind the control panel. I would believe that if you had a set of these pages and the interest that you could at least try the calibration and diagnostic tests yourself. Whether you can fix it yourself depends upon the specifics of the problem.
If the two heater hoses are both hot, then there is good circulation. The reasons for insufficient heat could be:
obstructed air intake at the cowl, obstructed heater system outlets, blend-air door not functioning properly. If the temp cannot be controlled the reasons could be: blend air door binding, faulty blend air door motor, improper coolant temperature, faulty instrument panel control. Going thru the diagnostic tests should sort out which of these is the cause. The actuators for the various doors can be serviced without removing the unit, but the doors themselves to be serviced requires removing the unit from under the dash.
I would be pleased to xerox copy the pages (40) that descibe the unit and the tests and servicing, and the pages (8) that show the wiring diagrams. This would cost me about $4.00. The postage would be about $ 1.60. You could mail me back 17 39-cent stamps to cover these costs after you received the pages if you prefer to get these quickly.
It is obviously something that I can't walk you through without having these reference materials. Also I do not personally have a van or experience trying to repair this system. So the written materials are the best I can offer.
Roland