Refrigerator Troubleshooting. Oil pressure failure switch
This method is typically used to include compressors oil pumps and on several compressor systems. Management function is to stop the compressor(s)when oil pressure developed pump falls below a certain level, or if the oil pressure is not possible to achieve the maximum safe level for the desired period after launch.
Oil pressure, as measured with a gauge, is the sum of the crankcase pressure (suction) and pressure arising at the pump. Rejection switch should be set to work in the " useful " pressure, not on the total pressure. To define a useful pressure (provided the correct lubrication of the compressor), subtract the suction pressure from the total pressure. Since the oil pump works only when the compressor is running, the total pressure is equal to the pressure in the crankcase during cycles.
When the compressor starts, oil pressure rises to the cut-in switching point.
Differential switch will open and break the chains of the heater and the compressor will operate in normal mode (see Fig. 90).
If the effective pressure does not rise to the cut-in point within the time limit (60 to 180 seconds), differential switch contacts will not open and the heater will remain in the circuit. This causes a bimetallic strip in terms relay deformation and open the synchronization of contacts, which will break the chain starter coil and stop compressor. Similarly, if the useful pressure falls below the cut-in point in the process of exploitation, differential switch is closed and the power of the heater. Time relay compressor stop after the time delay feature of the switch. The controls are available with 60 and 90 seconds of delay, but it must be realized that the time is not changed.
The most current oil pressure refusal switches are provided with terminals for connection to a crankcase heater. Since the terminal arrangements vary, reference shall be made on the wiring diagram supplied with the switch.