Heater issues

[socrates60]

I recently had to replace the little electronic control module for the climate control that controls the vent switching (I was only getting air out of the dash vents). Anyway now it seems like the temperature control isn't working right. If I crank the temp up I will get warm air out for a second or two, but then it seems like all it's doing is blowing cool air from the outside, and no matter what I do with the temperature control it doesn't affect it.

So is it possible my heater core has gone bad, or is it (hopefully) something simpler? Like I said it will blow warm air out for a second or two, but then it's just cool air--almost like the flow from the heater core is being shut off.

Thanks for any help/answers.

[elecfus]

a heater core is exactly like a radiator. a bad heater core will leak coolant into the foot well.

when you turn the climate control switch to hot it opens a valve that lets coolant flow to the radiator core.

testing proceedure:
manual control unit:
check the actuator cable is connected and moves smoothly.
run car, move the actuating lever with the cable to manually open/close the valve.
digital control:
warm engine to operating temperature so that the radiator bypass valve actuates
disable recirc, econ, mode and fan options
switch control module to defroster only setting. this forces it to only try to blow air through the heater core.

at least now you know if it will blow hot air.
next, enter self diagnostic mode by holding down auto then holding down off at the same time for 5 seconds. take finger off 'off' first then auto, you are now in testing mode. press off to cancel.

there's about 50 pages to the diagnostics so i cbf posting it all. just check the service manual.