There are several important accessories needed for an attic install. However, in our opinion, the two most important are: safety cutoff switch and drain pan.
This is designed to cut the unit off whenever the drain is overflowing. Drains overflowing are most commonly found from a clogged drain line, say for example: a insect as built a nest on the outside of the drain line, or dirt has built up blocking the drain line. Whenever this happens water from the AC system could backup, clog the drain, and overflow. This overflow could damage the ceiling, insulation, or other aspects of the attic area. Thus, a safety switch is a must have for an attic install.
In a similar sense to the safety cut off switch, a drain pan serves a similar purpose. It collects the water when/if an overflow does occur. Ideally, we would like a safety cutoff switch installed in the drain pan as well.
Here, at The HVAC Outlet, we recommend these accessories on all attic installs. And, your HVAC contractor should do so as well. If these are not present, and an issue does occur, then you could potentially have a significant issue on your hands.
A drain pan can be purchased over the phone at the HVAC Outlet. We would like to know the dimensions of the drain pan needed or the air handler or furnace being used. The drains pans vary in size depending on application.
A safety cut off switch can be purchased here.