An improved control over the pressure vented or tapped to a back pressure chamber in a scroll compressor is achieved by maintaining a vent hole closed for the majority of the operational cycle of the scroll compressor. The hole is preferably selectively exposed to a discharge pressure for a small portion of the cycle, and to an intermediate pressure for a second small portion of the cycle. Other than those two small portions, the hole is preferably closed. The invention reduces pulsation in the back pressure chamber and also reduces pumping losses caused by fluid moving into and out of the back pressure chamber through the hole. In one embodiment, grooves are formed in the fixed scroll member to communicate a selected intermediate pressure and a discharge pressure to locations on the base plate of the fixed scroll member. A vent hole in the wrap of the orbiting scroll member cyclically moves over the two grooves. The vent hole is closed by the base plate of the fixed scroll member for the majority of its operational cycle. In a second embodiment, a pair of holes are formed through the base plate of one of the scroll members. The holes are covered by the wrap of the other scroll member for the majority of the operational cycle of the scroll compressor. Each hole is open for a small portion of the operational cycle to selectively tap an intermediate and discharge pressure to the back pressure chamber.