Digital Zeus™ HVAC Tool & Instruments Journal

Most reference books will refer to compressors as the heart of refrigeration systems. If that’s the case, then the reversing valve would have to be the lungs, or liver, or kidneys of a heat pump system, for it is the component that determines whether the system runs in heat or cool…The reversing valve may be a mystery to some. They are in fact, an assembly of two valves: the main valve which actually directs the refrigerant flow in the system, and a pilot valve which controls the main valve. The pilot valve applies system pressures to the ends of the main valve, suction pressure to one end, discharge pressure to the other, creating a pressure differential which will force the main valve plunger to slide in one direction or the other. This design allows the heat pump system pressures to actually switch the reversing valve position. A solenoid capable of switching the main valve directly would, no doubt, be very large. I’m oversimplifying the design and operation a little, but my intent is simply to summarize the function of the valve, because if it fails mechanically, your only option is replacement…an intimate knowledge of the inner workings turns out to be academic. 


 
Valve failures will generally be 1) solenoid coil failure, 2) “stuck in heat or cool” position or 3) stuck somewhere between heat and cool positions. Coil failure is usually fixable. You only need to verify the absence or presence of coil voltage in the appropriate cycle, to eliminate wiring problems. Coils can short out or go open and in most cases, a new coil can be substituted.Stuck valves could be the result of a pilot or main valve problem. In either case, I’ve had no luck in making a “repair”…In my personal opinion, “unsticking” a valve is only temporary…it will most likely stick again. I don’t recall ever seeing a valve stick one time only. But if you determine a stuck valve is the case, you can try freeing it by raising the head pressure. To do that simply electrically disable whichever fan motor is providing condenser air. If stuck in “cool”, the outdoor fan motor…if stuck in “heat”, the blower motor. I usually let the head pressure run up to 375-400 psi (R-22) or so. Obviously, this technique offers some inherent potential system hazards, so evaluate the entire situation carefully before you decide to do it. No advantage to creating a new problem, in attempting to correct another.

The Wisdom of Wayne Shirley Available at http://www.wayneshirley.com and http://www.hvacprotech.com Master the Heat Pump. Read the Rest of This Article: http://hvacprotech.forumwise.com/hvacprotech-thread3179.html