A cover for the bulb of a thermal expansion valve is comprised of two halves of an insulative body that are wrapped around the bulb and associated outlet types in clamshell fashion to encapsulate the combination. Internal and external flaps are hingedly connected along their longitudinal edges to permit access for inspection purposes, and the external flap is secured to the internal flap by Velcro. A tongue structure on the outer surface of the body fits into grooves on the inner surface of the outer flap to seal the cover against the entry of moisture. The two halves are secured in place at their ends by way of bands.