A gas turbine engine includes a first tap connected to a compressor section to deliver air at a first pressure. A heat exchanger is downstream of the first tap. A cooling air valve selectively blocks flow of cooling air across the heat exchanger. A cooling compressor is downstream of the heat exchanger and pressurizes the air from the first tap to a greater second pressure. A shut off valve selectively stops flow of the air between the heat exchanger and the cooling compressor. A controller controls the cooling air valve, the shut off valve, and the cooling compressor such that the flow of the air is stopped between the heat exchanger and the cooling compressor only after the controller has stopped the cooling compressor. A monitoring system communicates with the controller and includes a pressure sensor and a temperature sensor downstream of the cooling compressor.