The introduction of outside air with highly variable load creates the need for variable-capacity systems. APR Control enables the system to match capacity with changing load conditions.

Local and national building codes require ventilation rate minimums to address potential health issues. Proper ventilation rates contribute to improved indoor air quality, which not only contributes to healthier indoor environments but also improves the productivity of occupants. Most cases of sick building syndrome can be directly traced to inadequate ventilation.

For cost-effective solutions, many engineers and contractors look to the APR Control to give their systems the necessary range of control; from 100% outside air for lab applications to 25% for conference rooms. The APR Control has provided cost-effective solutions for all types of outside air concerns.


At the turn of the millenium, a school building in Maryland had a mold growth problem in some of its classrooms. As a result of oversized air conditioning systems and high amounts of outside air (as demanded by ventilation codes), the simple thermostatic controls were satisfied quickly, causing compressor short cycling. The reduced system runtime increased humidity levels during unoccupied periods.

Following installation of the model APR-1D Control (for R- 22 refrigerant), the 4-ton systems were given the ability to run at as low as 1.5 tons, extending the runtime significantly. This reduced humidity in the space that was the primary cause of the mold growth.