Korea and some other countries located in the northern hemisphere employ the air conditioner for the space cooling in the hot summer season and also some kinds of heaters for the space heating in the cold winter season. Especially in Korea, a great number of air conditioners of about 12,700,000 sets have been used these days. However, they are used for a short operation period of only 58 days a year, which results in the material and economic losses. To solve this problem and employ this system for the emergency shelter, a new conversion unit which could convert the existing air conditioner to a heat pump system for simultaneous heating and cooling was developed in this study, and the thermal performance was tested. The results indicated that the indoor air could be heated from $27^{circ}C$ to $39^{circ}C$ by the air conditioner converted to a heat pump system with the ambient temperature variation of $-10^{circ}C{sim}10^{circ}C$, and cooled from $20^{circ}C$ to $15^{circ}C$ by the converted system with the ambient temperature variation of $20^{circ}C{sim}35^{circ}C$. And also the heating COP increased from 3.3 to 5.3 in case of the heat exchange of the super cooling(HESC) circuit and from 3.0 to 4.0 in case of the By-pass with the ambient temperature variation of $-10^{circ}C{sim}10^{circ}C$, respectively, whereas the cooling COP decreased from 3.1 to 2.1with the increase of the ambient temperature from $20^{circ}C$ to $35^{circ}C$.