There are only a few reasons your 75F device will appear to be power cycling.
- Low voltage. If your device is flickering on and off it may mean your transformer is weak and should be checked.
- Weak Transformer. If your device only appears to power cycle at wider intervals that are seemingly random. It can be that it is associated with a control relay energizing and pulling down a contactor shared by the same transformer. In this case the transformer may have enough power to power the device, but not the device and the contactors.
- Loose Wire. If your device is power cycling at truly random intervals it may be that there is a loose wire somewhere on the power bus.
- Safety Interlock: Sometimes a safety (condensate pan switch, high/low pressure limit, etc.) is wired so that it will break the power or common to a thermostat or controller. Trace power wiring to ensure interlocks are not causing the power cycling.