Many service technicians experience service calls where the compressor has both a low head pressure and a high suction pressure. Often, the refrigeration equipment is still running, but the product temperature is suffering about 7° to 10°F. These calls are tough to handle because the compressor is still cooling, but not cooling to its rated capacity. The medium-temperature products will spoil quicker and the low-temperature products are not frozen as solid as they should be. They will also spoil sooner.
There are three main reasons why a compressor will simultaneously have a low head pressure and a high suction pressure: Bad (leaky) compressor valves, worn compressor rings, and a leaky oil separator.