Heat Pump Not Cooling? The Reversing Valve Could Be To Blame

18 March 2016
 Categories: , Articles


With the spring season under way, there's a good chance you're shifting your focus from heating to cooling your home. Unfortunately, reversing valve issues can prevent your heat pump from making the same transition. The reversing valve is what makes it possible for your heat pump to switch from heating to cooling mode on demand. Problems with this component could keep your heat pump locked in heating mode. The following takes a look at the common reasons behind reversing valve failure as well as a few solutions to help get your heat pump back on track.

Common Reversing Valve Issues

Dirt and debris can accumulate within the reversing valve, causing the main slide to stick in place. Ordinary wear and tear can also cause the solenoid operated pilot valve to fail, leaving the valve locked in place. Both issues can freeze the heat pump in heating mode until they've been corrected.

A reversing valve leak can also make it difficult for to heat pump to transition from heating to cooling mode. The symptoms of a leaking reversing valve often resemble those of a failing compressor, which could make it somewhat difficult to correctly diagnose the problem.

Fixing Stuck Valves

Diagnosing and temporarily fixing a stuck reversing valve is a relatively simple affair. After locating the reversing valve on your heat pump, give the valve a couple of taps with the rubber handle of your screwdriver. In most cases, this will dislodge the debris holding the slide in place and allow the heat pump to switch to cooling mode.

Unfortunately, the reversing valve will likely get stuck later on as long as the debris remains in the refrigerant lines. Not only will you have to replace the reversing valve in its entirety, but you'll also need to have the refrigerant lines purged and thoroughly cleaned before adding new refrigerant.

Fixing Solenoid Issues

You'll need a multimeter and an unmagnetized screwdriver in order to diagnose solenoid-related reversing valve issues. The valve itself is usually located next to the compressor within the outdoor cabinet of the heat pump system:

  • Start by setting the mode switch on your thermostat to "cool."
  • Make sure your multimeter is set to measure "volts" and check for power at the pilot valve solenoid. The solenoid receives 24 volts of power when energized, so this is what you should see if the solenoid is receiving power correctly.
  • If there's no voltage at the solenoid, check for power at the low voltage transformer and the wiring circuit leading from the reversing valve.
  • If there's voltage at the solenoid, check for resistance by placing the blade of your screwdriver at the end of the solenoid. The solenoid should be able to magnetically pull the screwdriver blade towards it when activated.
  • Disconnect the wiring harness attached to the solenoid and, with your multimeter set to "ohms," measure the amount of resistance at the solenoid.

A good solenoid should read anywhere from 10 to 60 ohms. If you get a reading below that threshold, simply disconnect the solenoid from the reversing valve and replace it with a new solenoid.

Diagnosing Valve Leaks

As mentioned before, diagnosing a leaky reversing valve can be somewhat difficult since it shares its symptoms with those of a failing compressor. Fortunately, there is a way you can rule out compressor failure. However, you may want to have your HVAC contractor perform the following steps, as he or she will have the proper tools and expertise needed to complete this task:

  • Connect your refrigeration gauges and make sure the heat pump is turned on but with the compressor motor turned off.
  • Wait for the head pressure to build up to 475 pounds before switching the unit off. In the meantime, place one hand on the reversing valve suction line and the other on the dome of the compressor. The former should heat up faster than the latter in the event of a reserving valve leak.
  • After the desired head pressure has been reached, listen out for the sound of hot gases pushing past the source of the leak. In most cases, you'll hear a hissing noises originating from the reversing valve.

After confirming the reversing valve leak, your HVAC contractor will likely replace the entire valve with a new one. This should also be left to your contractor since the removal and installation process involves brazing the copper piping connecting the reversing valve to the rest of the heat pump unit. Contact your local plumber for more info