Unplugging the device for several minutes has been done. Many times. I need to do it three times before it lets me open the door. I tried changing media brands, always with the same effect. I am pretty sure the thing is kaput, but I posted here hoping to hear of a software update unknown to me before buying a new recorder. Thanks.

The plenum sensor will help prevent freezeups but if the cause of freezing is the A/C unit not low airflow from only one zone calling, it won't. Since you have a single stage A/C, having Y2 call means nothing. It shouldn't even be wired up. If it is, it is wired wrong though that isn't the cause of your problem. Your A/C should be wired to Y1 and nothing on Y2. What do you have the cool limit set to? I'd go no lower than 45, try 50 even. So they say the A/C is running just fine? Something is fishy. We use that panel with 3 zones at our office. Single stage A/C, 2 stage gas furnace. Has worked flawlessly.

Can't access my email for the last hour. Message says they are 'over capacity'. Uh-huh. Right. Like *never* happened before.

I hear what both of you are saying about quility of material changing with time. It's invitable as I see it, when seer ratings came into the lime light, mfgr A reduced wall thickness to better transfer heat,mfgr B&C followed and the race was on. It go's on and on with cost cutting to remain competive. What is inexcusable is quility of work done in the field. I noticed the biggest turn in the early 90s when EPA got involved then licenseing hvac contractors became required. I leave each to his own while judging EPA but here's a fact about hvac license in Texas (at least until I retired 8 years ago). Unlimited locations in every city in Texas can operate under the license of one person. A retorical question,does anyone see that kind of licensing as benificial to consumers? Conincidently there's an active thread over in home repair about licensing the trades if anyone care's to take a peek. Many mom and pop hvac companies were run out of business by those two developments. The horse is starting to ride the man and the horse is getting fatter by the day. Rant over. For those interested in finer points about evap coils damaged by ice. Copper "work hardens" and become's less pliable each time it's bent or otherwise stressed. Repeated freeze thaw cycles progressivly work hardens tube until cracks develop. What you might ask can the average tech do with that knowledge? If Jim bend's a line set then change's his mind,straighten's it out and rebend's only to have Joe show up to tell him it's wrong and once more straighten and rebend yet again,chances are the pipe will collaspe and/or break. If only Joe knew how to "aneal" the line it might be restored to a state of pliability saving the price of a new line set. At minium as Austin said the compressor is harmed during freeze up and fixing it asap is prudent.