Chrysler Repair: 93 Minivan lack of heat, plymouth grand voyager, heater control valve

Question
QUESTION: Hi,I have 93 Plymouth grand voyager that is putting out very little heat except momentary after it's sat after the engine is warm. I've power flushed all the lines and replaced the heater control valve due to cracking. The control panel appears to operated the floor,dash vents ok and the incoming fresh appears to be working. It's almost like the heater core is getting no H20 yet if I disconnect the outgoing line H20 is slowly circulating. 240K mi if it matters. Thanks for any insight and I apologize for submitting an older vehicle but it's almost a generic ?   Richard

ANSWER: Hi Richard,
The diagnosis involves a couple of possibilities: heater core coolant flow rate and blend-air door function.
On the flow: when you have operated the heater and the engine long enough for the coolant temp to reach normal (I presume the temp gauge is at mid-scale or so) feel the in and out going heater hoses at the firewall to see if they are of nearly equal temperature, which they should be. That would corroboate you have good circulation. If not, then verify that the heater control valve has been actuated by the vacuum line (it should only change position when you go to recirc AC position which cuts off, by-passes, the flow through the core). If that is working then another possibility if you have the 2.5L 4 cyl is that you have air trapped in the core. Let me know if that is the case.  Otherwise, it suggests the core is clogged and you need to back flush it (and if that doesn't work then change the heater core).
On the door function: there is a cable attached to the lever which connects to the air door lever. When you move the temp lever does it feel like it is moving something? If not, then there is a mechanical disconnect issue between the temp lever-cable-air door lever. Unfortunately there is a fairly large amount of dash disassembly required to fix that. I can xerox the pages from the '93 manual that shows how that it done and postal mail it to you.
'No problem' with the vintage of your van. I have manual that go back to '82 so this is right up my alley.
Roland
PS Use the "thank/rate" tab below to get back to me without having to wait for me to be 'available' to take a question. Use the comments section.

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QUESTION: Hi Roland,

The in/out lines from the core seem the same temp and while I had the heater control valve off I actually did a high pressure flush of every coolant line and removed a lot of rust and debris.The flow seems very good to and from all hoses. The heater door feels like it's moving well as you can feel a thump on the heater box with my hand and the flow seems to be altered. I do have all the dash apart but was hoping not to have to pull the box.It is a 3.3 if that matters. I have forced the heater control valve into the closed and it has no effect.

Answer
Hi Richard,
If the door inside box seems to be sounding like it is moving, and you have good flow through the core, then the only other possibility is that the coolant temp is lower than normal due to an engine thermostat that is opening at too low a temp. You might want to see if the system is pressurizing and maybe use a thermometer to check the coolant in the radiator before it pressurizes to access if it is moving to be in the range of 220F or not. Other than that, I can't think of anything else unless the "thump" is something other than the door itself (such as the lever/door interface is broken and the air is not really being diverted through the heater core). Closing the heater by-pass valve should maximize the core flow. If you can see the temp cable/door lever interface observe what happens when you move the temp lever.
Roland