There are two cooling solenoid valves that control compressor cooling located behind the side service cover in the upper left hand corner. These solenoids are connected to the backplane by plugs. There are LED´s above the plugs on the backplane that indicate when the solenoid is energized.
In the TT300 and TG230 Model Compressors, the cooling path is serial. First to the Inverter and SCR´s, then to the motor. Vapor from the cooling process is recovered between the stages of the compressor. One solenoid is routinely opened and closed to control cooling. If one solenoid is open and temperatures in the inverter/ compressor continue to rise, the second solenoid will open to provide additional refrigerant flow through the cooling circuits.
Other TT model compressors The left hand solenoid is the Motor Cooling Solenoid and the right hand solenoid is the Inverter/ SCR Cooling Solenoid.
The BMCC card sends signals to control the Cooling solenoids. However, the relays to control these solenoids are in the Serial Card.
There are temperature sensors under the inverter, the SCR´s and in the motor cavity.
The compressor controls have upper and lower limits for the temperatures in the Inverter and the Motor Cavity. When the temperature measured is above the lower temperature limit and rising, as the measured temperature hits the upper limit the appropriate cooling solenoid is opened. As the temperature begins to fall, once it hits the lower limit, the appropriate cooling solenoid is closed.
Under normal compressor operation, you should be able to watch the inverter and motor cavity temperatures rise and fall as the cooling solenoids are opened and closed by the compressor controls.
If you do not see these temperatures cycling, you will need to investigate further.