I replaced the heater core and now the only thing that operates is defrost and the automatic ventilation system when the heater/ac is off. The defrost air is not hot or cold. The ac compressor is working. Everything was working before I replaced the heater core. I think I reistalled all of the hoses correctly. The hose is hot going into the heater core on the engine side of the firewall but the return hose is not. The interior filled up with steam when the heater core leaked. I wonder if one of the sensors were damaged. Is there any way to test any of the sensors? Any help would be appreciated. THANKS!
The sensors are easily tested variable resistors -- tested with an ohmeter. The service manual has the values. That said, it seems much more likely that you may have missed a vacuum hose or electrical connector somewhere.
Sensor failure (all else being correct) will typically lead to full hot or full cooling. Since to change the heater core you removed the programmer/controller and a lot of vacuum lines a well as disconnecting the mode door operator ( the shaft that extends vertically out of the Programmer) bell crank. I would look to an incorrect re-assembly of the components by using the diagrams in the Factory Service Manual first with an emphasis on the vacuum lines, the electrical connector to the programmer and the correct orientation of the mode door bell crank.
Greg Surfas