I am at my wits end with this air handler. I have replaced the the transformer 7 times in the last 3 months. I have replaced every component in the control box, the heat strip and replaced the control box itself. I've also replaced the thermostat in hopes that this would resolve the problem. The system is a First Company Horizontal Fan Coil HX series pumping R22 through a Bryant 3 ton condenser. This problem begin during the summer. The resident would get at least a week of no problems with the condenser and then the transformer would blow. We are now in heating season and as soon as the 10Kw strip is energized, there goes yet another transformer. Any ideas of what may be causing this aggravation and why it isn't happy with heating or cooling?