4 Way Reversing Valve

Here is another view of how the 4 Way Reversing Valve diverts flow; the pipe on the single stub side of the valve is always the discharge from the compressor. The discharge is diverted to the condenser, the middle stub is always suction going to the compressor, and the left over stub is always from the evaporator. The switching function is accomplished by the sliding back and forth of an internal barrel which has diverting passages. The systems own high side pressure is used to ram the barrel to the desired end by a pilot duty solenoid valve. On the diagram below, click back and forth between Buttons 3 and 4 to see the barrel slide to opposite ends. Then try Buttons 5 and 6 to see the refrigerant flow being diverted.

Liquid Line Check Valves & Bi-Flo Driers

The Liquid line always carries liquid but the direction of flow reverses in each mode. Each coil has it's own metering device with a check valve piped in parallel. When refrigerant flow meets a check valve in the blocked direction it has no choice but to divert through the TXV. When refrigerant flow meets a check valve in the allowed direction it will take the route of least resistance and go through the check valve and ignore the TXV. There are TXVs that have this check valve function built right into the valve itself. The Bi-Flow filter/drier works in a similar manner. Inside a bi-flo drier there are check valves which ensure that refrigerant flow goes through the drier core in the same direction regardless of the liquid line flow direction. The drier core must experience flow in one direction only. Otherwise, if counter-flow was allowed debris that had been filtered out would unload and re-enter the system.
The accumulator attempts to protect the compressor from liquid refrigerant in the suction line. This is accomplished by use of an inverted trap. However at the same time it can trap oil entrained in the refrigerant. This could eventually hold back the entire oil charge which would cause compressor failure. To overcome this problem a small orifice is located on the underside of the inverted trap. A Venturi Effect occurs and any trapped oil is sucked through the orifice and carried away by the suction vapours to be returned to the compressor sump where it belongs.