Cold Heater

OK so everything else works but you get no warm air regardless of the settings, AC also works? From the description it sounds like either the blend door is stuck closed, the control head is still a problem or the heater core is plugged. To figure out where the issue is you are going to need some testing. To check the core run the engine for a while and be sure that both hoses get hot, that would show that coolant is going through the core. Next to check if it's the door you need to remove the actuator and with the fan on and a warm engine reach in with a screwdriver or similar to move the door shaft. If you move it do you get heat? If yes you know the door works but isn't being moved by the actuator. However as you say the temp lights are flashing that usually indicates that the control head cannot control one of the actuators, it may not be the blend door actuator though as a failure in any of them can cause the error. Unfortunately testing the control head and the actuator on those is difficult if you don't have the proper test device. Being a 94 you might find a shop that still has the tools to test it, the other option is to replace the other actuators and see if the system comes back to operation. Did you use an OE actuator for the electronic climate control? There are two different ones. GM #89018368 is the one you want according to GM. The other one looks the same but doesn't provide feedback.