I have a vertical closed non pressure system w 2 command aire heat pumps. They are controlled by 2 Ranco temp controllers. When heat is called Heatpump one kicks on, and after timer delay, heat pump 2 kicks on but will only run for about 30 seconds. And turns off. I was worried thinking compressor was bad but....I unhooke safety switch wire on HP1. (Running Heat pump) Called for heat, heard contractors click but compressor didn’t start because switch unplugged, after timer delay HP 2 fired up and ran perfectly heating buffer tank as it should. This tells me unit is fine. Question why won’t both run together like it’s designed to. System is 12-13 years old. Once winter kicks into full gear, one pump can’t keep up and ancillary heat will destroy electric bill. I’m thinking temp controller but any suggestions appreciated.