This was designed especially for adding cooling to an existing forced-air heating system. As shown on page 39, a cooling-coil section is put above the heater and pipe-connected to the cooling compressor, which is usually located outside.
Refrigerant is pumped to and from the cooling coil section is put above the heater and blower works the year round. In summer, the house air is pulled through the furnace (which is then inoperative), blown through the add-on cooler for air conditioning and distributed through the existing ducts.
The add-on unit is the most inexpensive if you start with a good forced-air heating system. For one thing, you usually save the cost of a cooling fan by using the furnace fan. For another, you use the ductwork already installed. And the remote compressor section can be bought with an air-cooled condenser so no water is needed. Total installation costs start at about $1,200 fora 2-ton size, the more complex the installation the higher the cost.