Valve failure are: the valve can not be commutated or commutation slow, gas leak, electromagnetic pilot valve and so on. (1) The reversing valve can not change direction or change slowly, usually due to poor lubrication, the spring is stuck or damaged, oil or impurities stuck sliding parts and other causes. In this regard, should first check the work of the oil mist is normal; the viscosity of the lubricant is appropriate. If necessary, lubricate, clean the sliding part of the reversing valve or replace the spring and reversing valve. (2) After the valve is used for a long period of time, the sealing ring of the valve core is prone to wear and the valve rod and the valve seat are damaged. As a result, gas leakage in the valve, slow or abnormal valve operation, and other faults can not be reversed. At this point, the seals, stem and seat should be replaced or the reversing valve replaced. (3) If the electromagnetic pilot valve into the vent hole is clogged with debris and other debris, closed laxity, the activities of the core is stuck, the circuit is faulty, etc., can lead to the reversing valve can not be reversed. For the first 3 cases, clean the sludge and impurities on the pilot valve and movable iron core. The circuit failure is generally divided into two types of control circuit failure and electromagnetic coil failure. Before checking the circuit fault, the manual knob of the reversing valve should be rotated a few times to see if the reversing valve can be normally commutated under the rated pressure. If the commutation is normal, the circuit is faulty. Check, the instrument can measure the voltage of the solenoid to see if it has reached the rated voltage, if the voltage is too low, you should further check the control circuit power and the associated trip switch circuit. If the reversing valve can not be changed normally under the rated voltage, check whether the electromagnetic coil connector (plug) is loose or inaccurate. Method is, unplug the plug, measuring the resistance of the coil, if the resistance is too large or too small, indicating that the electromagnetic coil is damaged, should be replaced.