I have beeb working on a new EMI 3x multi heat pump. I replaced the reversing valve and operation to the unit was restored, the following month the same thing happens, once again the the valve was replaced and operation was restored, here we are 3 months later and the unit is down again. all repairs were performed with a nitrogen purge, 3 evac, heat paste and a wet wrap on the valve. I have never in 13 years had a revesing valve go out more than once. The only explaination would be a bad batch of valves made at the factory, but those odds are slim. any ideas?