HVAC control systems and their wiring are somewhat complicated to most AV integrators. Having worked in the HVAC field for a while back in high school and being a c4 diy er with a c4 thermostat, I can imagine where most HVAC installers won't know exactly how to wire in the c4 thermostat nor will they care much about working with an integrator on adjusting the settings(max runtime/min runtime, etc) on the control board of the AC unit. Most LV/AV integrators don't know that some/most brands of HVAC systems have adjustable settings besides the thermostat.