GO system ground loop 5 ton cooling season ok! Heating get about 75 deg big red light Test code FP1 fault water coil freeze protection. Thermistor check ok. Believe the sys is functioning right leaning towards ground loop water flow. Flow controller motors are running. Question what should be the psi reading on the loop? The gauge read 0. The compressor ices up the unit heat exchanger gets quite cold. The company that installed went out of business.

thanks John