Reversing valves don’t often fail, but when they do it can cause a lot of confusion while troubleshooting. There are three main things that can cause a reversing valve to malfunction:
- The valve is stuck in the heating or cooling position.
- The coil is defective.
- The valve is leaking internally.
1. If the valve sticks, it will not change from the heating to the cooling position or vice versa. Make sure the reversing valve is energized. Use your voltmeter to ensure the proper voltage is at the solenoid coil, then hold a small screw driver close to the coil to see if there is a magnetic field present. If the coil is energized, check to make sure there is a pressure difference between the high side to the low side when the unit is running. The reversing valve is a pilot operated valve and requires a pressure differential to operate.
If you suspect the valve is stuck, take a soft object like the plastic handle of your screwdriver and tap on either side of the valve body. This may free the valve. If it does, force the valve to change positions several times to verify it is operating freely. If it does, the problem may be resolved. If the problem reoccurs, the valve should be replaced.
2. A defective solenoid coil will not energize the valve in the cooling mode. (Some manufacturers energize the valve in the heating mode, make sure you check). This can be determined by using the voltmeter and screwdriver test outlined above. If there is voltage to the valve and no magnetic field present, the coil has an open circuit. In this case, only the solenoid coil needs to be replaced.
3. An internal leak in the valve is difficult to troubleshoot and is often confused with a compressor that is not pumping to capacity. Both a leaking reversing valve and a failing compressor have the same symptoms – both the heating and cooling capacity of the system are diminished. This is because the compressor continues to pump the gas around and around inside the leaking valve and usable refrigeration is lost in the process.
When a reversing valve leaks, it leaks from the high side to the low side. To check for a leaking valve, measure the difference in temperature between the suction line from the evaporator and the permanent suction line on the reversing valve (usually the middle line on the bottom). The temperature difference should not be more than 3F. If the temperature differential is greater than 3F, the valve must be replaced.
Note – Take the temperature at least 5 inches from the valve body to keep the temperature of the valve body from affecting your reading.
Keep these three procedures in mind, and when you come across a bad reversing valve it will be a cinch to troubleshoot.
by Ron Walker
