I just replaced an old 4 wire thermostat with the Hunter 550. AC and heat work fine, but it seems the digital thermometer is stuck on 70. I can adjust the thermostat to above or below that, and the system responds accordingly.

Did I miss something in the installation or does it seem like the unit is defective?

"digital thermometer is stuck on 70" so if you set the stat to heat to 75 and it heats and kicks off your thermometer still reads 70, is that what you are saying?

Almost. If I set it to 75, the heat kicks on and will never turn off because it still reads 70 on the thermometer.

OK we are going to start at square one. Read http://www.hunterair.com/ssi/pdf/hunter/44550-Owners-Manual.pdf page 6-7 step #1 did you remove the mylar label from the display, this label reads 70 but it is a printed see through label

Wow... I'm trying not to be insulted, but I guess its as common as "did you plug it in" resolutions. Yes, the mylar label was removed. My process: I turned off the system, removed the old thermostat, installed the mounting plate attached the four wires accordingly (W,Y,G,Rc), snapped in the thermostat, turned the system on, programmed the thermostat, then watched the temperature reading never change from 70. The system will run forever unless I turn it off or if one of the programs are set to 70.

I appreciate your help.

No insult intended but Hunter put that in their instructions because initially it was not there and they had problems. From what you are saying I am thinking defective. Can you still return it?

I was able to reach someone at Hunter. They're certain its defective. Even though I just opened it, I bought it over a year ago and they won't exchange it without a receipt. Trash can for me unless someone is interested in buying a broken stat.

Thanks again ballengerb1.