Tag Archives: REVERSING VALVES

Replacing A Reversing Valve

(The content of this post is intended for consideration by trained service personnel only)

Replacing reversing valves is one of the more taxing repairs to heat pumps. I’m sure every tech has his preferred method for doing it, which probably depends on his personal level of confidence, skills and dexterity with a torch. The primary objective (for me) is getting the new valve in, without destroying the internal heat sensitive components. The valve body can only withstand temperatures approaching 250 F degrees…which ain’t much considering the 1400 F or so necessary to get a good braze joint.

And you have to consider in most cases, the valve is in a position where you can’t just “sweat” it out. There has to be some “slack” available and usually isn’t. Even if you have the special torch attachment that can heat all three tubing connections simultaneously, you still need room to pull the valve away from the tubing. Even if you manage that, you got to consider brazing in the new one without burning it up.

So, I usually study the “geometry” of the valve and try to cut the tubing in places I can easily access on the re-braze…Then, once you get the “assembly” out, you can heat the connections in whatever manner you prefer and remove the old valve.

Then, you only have to braze in the new valve one tube at a time, allowing you to use wet rags or whatever, to keep the valve body cool.

Once you complete that step, using swaged ends or couplings allows you to reconnect the cut joints.

TROUBLESHOOTING HEAT PUMP SYSTEMS…REVERSING VALVES

(The content of this post is intended for consideration by trained service personnel)

The reversing valve is the component of a heat pump system that determines whether the system runs in heat or cool. 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 slide piece to shift 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”…I’ve “unstuck” a few, but the fix was only temporary. They most often stick again.

The last failure situation is the valve stuck somewhere between cycles, which is usually a difficult situation to diagnose. The valve slide position is such that the net result is a significant amount of leakage between low and high side pressures, producing symptoms of a faulty compressor…high suction and low head pressures.

There are several methods used by service people to confirm or eliminate the valve, involving tubing temperature measurements. More involved procedures amount to isolating the compressor, then eliminating it as the problem.

You can see a more in depth explanation of reversing valve operation and troubleshooting techniques in the “Diagnosing Reversing Valves” rental videos:

Diagnosing Reversing Valves

(The content of this post is intended for consideration by trained service personnel only)