I have a 7fbcu30 freezer truck that the free lift cylinder will not come down when it is cold. 30- -4 degrees f. Once it warms up it will function as it's supposed to. Fluid has been changed using aw68, cylinder valve has been checked, safety valve is stiff at first. I inherited this problem from a former tech. who could not resolve it. There is no binding in the mast itself. Once i loosen the safety valve the cylinder drops normally. I suspect the valve is sticking when the temp drops and frees up when it warms.