Chrysler Repair: Sporadic heater malfunction, chrysler lhs, 94 chrysler lhs

Question
'94 Chrysler LHS that intermittantly does not heat. It is an auto-temp system. Do you think it is the thermostat?  Serpentine belt replaced this summer, so has new coolant and new water pump.   Lori

Answer
Hi Lori,
I am less familiar with the LHS than some other models. Could you tell me which size engine it has?
If the problem were the thermostat, that would be shown by the temp gauge on the dash also being in the cold zone when you were not getting heat. So see whether that is the case or not.
There are several possibilities: there is a vacuum controlled heater by-pass valve that is used when you go for max cooling, and if that were coming into play incorrectly then the hot water would not get to the heater core at all. When you aren't getting heat, open the hood and see how the incoming and outgoing heater hoses (these are the ones that go thru the fire wall near the center) are feeling. If both are hot then you have flow thru, if one is significantly colder, then you may have a clogged heater core, or air trapped in the heater core.
The most useful test now would be to read the computer which operates this automatic system to see whether it has noted something to be wrong. By pressing the control buttons in the order shown, the unit will go thru a "self-test" that may tell us something:
SELF-TEST
Warm up the car
Turn off running lights, if on.
Pash the 'Panel' button momentarily
Display should light
Momentarily and simultaneously push the Defroster(symbol), Floor, and Auto buttons
1.All the symbols should light
2.Blower motor should go to highest speed
3.Air should be directed to panel outlets
4.Air temp should become hot then cool
If no to any of the above 4, let me know which.
Then either the display will return to the prior to test setting OR The blower will stop and the display will flash a failure code number between 1 and 18. Record the number and push the Panel button to resume the test (more numbers might be displayed, keep recording and pushing the Panel until the numbers stop coming out and the panel returns to pre-test appearance.)
Let me know which if any numbers came out.
So those are several possibilities to work on. Let me know what you learn/observe about them.
Roland