I have two GE Zoneline 5100 units in my condo, they have both been working fine for the past 8 years. I was out of town this week when the temperature dropped here in Chicago from 65 to 15. When I got home, one unit turned on and is working fine, the other is "dead". It is getting power (both are on the same circuit breaker), but it just won't turn on. Doesn't seem to be any kind of circuit breaker, fuse or other electrical reset I can perform. All of the DIP switches are set to "off". Is some kind of freezing protection activated? I haven't crawled out of my 19th-floor window to look for any ice on the outside...this has never happened before in the same kind of weather. If it helps: Model #AZ51H09DBDV1, Serial #GR888524