Customer stated heat pump has froze. Found heat pump locked out on low pressure fault code. Reset and checked running pressures and compared to manufacturers pressure recommendations on 22F Fahrenheit ambient. Current running pressures are 72/337psi, which are normal. Outdoor coil is clean. System went in 15 second defrost. Not long enough to thaw any ic build up on outdoor coil. Need to get pricing and availability on defrost board and defrost sensor.