Then run the self test. I don't have the key sequence in front of me, but do a search as it's been mentioned here a few times. See if the new head unit will run the test. If not, you have a bad head unit. Got two off eBay that were bad. If it runs the test, but fails, then remove the actuator and run it again with the actuator hooked up, but not installed. Watch for movement in the actuator. One of the things the self test does is run the actuator through it's range of motion both ways (full hot and full cold) Also, when you replaced the head unit, did you replace it with the correct one? Did the color codes match? If not, who knows what will happen. Finally, if all that checks out, you have no other choice but to do the pinpoint tests in the manual. That will check your wiring for you.
