Is HVAC device a heat pump

first, if you have an air conditioner in your attic, then there should be TWO drip pans, and TWO drain lines.

• one of the drip pans should be built in to the air handler/coil unit
• the second drip pan should be at least as big as the entire air handler and coil unit, and positioned under the air handler to provide coverage for the entire unit
• both pans should have INDEPENDENT drain lines
• ideally, the second drip pan should have a float sensor unit it to shut off the system BEFORE it overflows.

either drain should be able to completely empty whatever amount of water you have in the pan within seconds. if it can't, then you have a clog somewhere.

also, the large drip pan below the air handler should typically be completely dry. it's there as a backup in case the drain line for the air handler clogs up. if you have any amount of water in there, then you have a problem somewhere else.

so, than being said, do the following:

• verify that both the air handler and the external drip pan have independent drains
• get a wet/dry shop vac and suck out both drain lines
• pour bleach down both drain lines
  • if you don't have a way to pour bleach down the drain connected to the air handler, make one. a simple way is to cut the existing line at a vertical run, splice in a T, then make an L shaped piece out of some tubing and an elbow. leave the top part unglued so you can remove it. see drawing.

• test your newly cleaned drain lines. remember, both drain lines should be able to quickly remove any water you pour in them. if they drain slower than your bathroom sink, you have a clog somewhere.

Air Conditioners and Heat Pumps and are just refrigeration systems. The following are the differences:

Air Conditioners

Dedicated cooling only systems are often referred to as Air Conditioners and have a single usage cycle that dehumidifies and cools the interior air in the living space. These are turned off in winter time for the obvious reason that you no longer need cool air inside and so often are winter-proofed to also prevent air leakage and precipitation intrusion.

Heat Pumps

Dual purpose heating/cooling systems are referred to as Heat Pumps and have a reversible cycle. They can be used to both Air Condition and Heat the living space by switching the direction of refrigerant flow.

In the summer time, they cool the interior by heating the outside atmosphere. In winter time, they heat the interior by cooling the outside atmosphere. Hence the name Heat Pump.

They run year around and therefore must have free airflow through them year around (not be winter-proofed with air-tight coverings). Having some sort of roof with clearance to allow free airflow and to keep the snow out would be a really good idea.