Upon arrival the system was in FP1 lockout and retry mode with 420 logged FP1 short cycles. Last visit to this house was Seth replacing the ABC board in November 2023. Hafter reset and retry I witnessed the system attempt to cycle on once and shut right back off within 2 to 3 seconds almost like a contractor chattering on and back off. After an additional retry with the system running the equipment appeared to be functioning properly with the FP1 sensor stable at 25 to 28° in low stage heat. After switching to high stage heat The system ran good for 30 seconds to 1 minute until it instantly dropped off to -3°f within two or three seconds and proceeded to lock out again on FP1. After investigating the control boards, wiring, sensors, and installing refrigerant gauges and water temperature sensors The system turned on and ran normal and exactly to book specs including refrigerant pressures, superheat and subcooling, water temperature drop and air temperature rise. All perfect to 30° wat