I have a York hvac system. AC works great. Heat is intermittent. I'll turn it to heat on thermostat and it may run for a while, but at some point (inconsistent as to how long), it turns from blowing warm air to blowing cold air. At times, I am able to turn everything off at the thermostat, wait 10minutes, and turn it back on and it works. I have someone coming out and don't want to play doctor but thought I'd ask this forum for any insight. Brrrr! Thanks! K