There's something different when it comes to the heat pump system. We know it runs like a regular air conditioner in the cooling season, but when we get to the heating season, some extra components come into play and we get confused or lose track of the sequence of operation for a heat pump. So let's go over some of the basics that even I have to review from time to time because heat pumps really are not my strongest suit. I have a video called Basic Heat Pump Operation that you might want to refer to if you need an even more stripped down version of the heat pump operation. This one's going to focus on the reversing valve or the switchover valve and what we should be checking to diagnose a heat pump that's not working or might be frozen over in a heating mode on a cold day. So let's quickly review some of the things that we learned in the last video. In cooling mode, the heat pump works just like an air conditioner. The refrigerant cycles through the system and basically makes the indoor evaporator coil a cold coil and the outdoor units coil the hot coil. We remove the heat from inside of the house at the outdoor unit and pull it to the outdoor unit to be released into the atmosphere. In heating mode, a reversing valve reverses the flow of refrigerant to make the indoor coil the hot coil and the outdoor coil the cold coil. So we're trying to extract the heat from outside and bring it inside, which can be done down to a certain temperature. The reversing valve exists to change the direction of the refrigerant. Twenty-four volts from the defrost board energizes the silenoid on it. On 90% of the systems out there, reversing valves default into heating mode. This way if the valve is not working or doesn't have 24 volts flowing to it, at least the heat will still work. That's because most parts of the country heating is more important than cooling is. Here in sunny California, we might disagree with that. The silenoid coil moves a pilot valve that creates pressure difference inside the reversing valve. Small capillary type tubes house that pressurized refrigerant and push the slide laterally to isolate two of the three holes leaving the reversing valve. The tube in the middle and the tube coming in from the top are attached to the compressor. The incoming line is always the compressor's discharge line and the middle tube of the three on the bottom is always the compressor's suction line. The tubes where the refrigerant is flowing in different directions whether in heating or cooling mode are on the two sides of that middle suction line. One leads to the outdoor coil and one leads to the indoor coil. In heating mode, which is the default mode in most systems, meaning the reversing valve silenoid does not have 24 volts coming to it, the refrigerant will be coming in from the cold outdoor coil up to the valve and then back down the middle suction line tube and make its way back to the compressor. Of course, you know from there the refrigerant is super heated in the compressor and discharge back to the top tube of the reversing valve and into the third tube where it's then directed to the hot indoor coil so that air can blow across that coil and send warm air into the duct system and onto the rooms of the house. In cooling mode, 24 volts is applied to the reversing valve silenoid from the defrost board. In this case, the refrigerant will be returning to the reversing valve from the cold indoor coil up into the reversing valve, back down the middle suction line tube and make its way back to the compressor. The refrigerant is super heated in the compressor, discharge back to the top tube of the reversing valve and into the third tube this time where it's directed to the hot outdoor coil. This way we have a cold indoor coil that the fan blows air across sending cold air into the duct system and onto the rooms of the house. What if the slider inside the reversing valve gets stuck? We all know parts fail electronically and mechanically. It can be easier to figure out the electronic problems because they're a little bit more straightforward. The slide inside the reversing valve is controlled by the pilot valve through pressure differential within the system at the time. So if system pressures are flat because the system has been off for a little while, the slider isn't going to move. Succeed and discharge pressures travel through the small cap tubes leading to the reversing valve, ultimately making the slider move. Things that slide get stuck and reversing valves fail by getting stuck because they got overheated or they inherited soot, debris and contaminants that resulted from a burned out compressor. Whatever is in those lines will make its way through the valve and what are the only two things that's allowed inside refrigerant lines. Virgin refrigerant and the compressor's oil. I've heard people say that a wax buildup can cause the valve to stick, but I can't really find any solid information on that. So if you know of this happening in different parts of the country, let me know in the comments down below. If you have the proper 30 to 70 psi of pressure differential in the system and the slide doesn't want to move back and forth inside the valve, let's make sure that there's 24 volts plus or minus 2.5 volts and make sure that's getting to the valve of silenoid. If low voltage is good to go, the silenoid's coil will create a magnetic field much like the one on a single pole contactor. Once energized, it'll pull the switch, activating the pilot valve, which in turn gets the ball rolling for the slider inside the reversing valve to move. You can test the silenoid coil to see if it's good or not by checking a few things. Make sure it's seated in the core or else the coil will draw excessive amperage and burn the coil up. With no power to the coil, check it for continuity with an O meter. If the meter reads O L or zero, the silenoid itself needs to be replaced. With 24 volts applied, it energizes the coil. Now you can remove the retainer that holds the coil in place on its core. Then you can move that coil back and forth along its core. And if the coil is good, a definite magnetic pull will be felt. You can check a coil out with your senses too. Visually and by smell. Visually you can check for any dark round coloration of the coil. But a telltale sign that you have a bad coil like this is its smell. A burnt coil puts off a very unique metallic smell that hangs around it for quite a while. It's the same smell that you get on a burnt motor winding because it's essentially the same thing. If the valve is not shifting, switch back and forth between cooling and heating mode. This will sometimes free the valve by creating a pressure differential greater than the 30-70 pounds that's required and maybe force the internal slide to shift. The last resort is lightly tapping on the body of the reversing valve. Take care not to hit the capillary tubes because they can easily be dented, damaged or broken. If 24 volts is applied and the coil is good, a definite clicking noise is heard as the coil moves along the core. If the coil is good and no clicking is heard, the pilot valve is defective. If we're trying to be in heating mode but the reversing valve seems stuck in a cooling position, we need to make sure 24 volts is not getting to the silenoid. If 24 volts is present, then the reversing valve thinks that it's supposed to be in cooling mode. If you remove the plug from the silenoid, does the valve switch over to heating mode then? Of course, the system has to have that 30-70 psi differential between the high side and the low side for the slider to actually move. If that pressure differential is there without 24 volts being applied and the valve won't switch from cooling to heating, the reversing valve is bad. Now if we're trying to be in cooling mode but the reversing valve seems to be stuck in the heating mode, we want to check to make sure that 24 volts is being applied to the silenoid. If it is, then check the silenoid like we've already talked about. Again, the system has to have that 30-70 psi differential between the high side and low side for the slider to actually move. If that pressure differential is there and 24 volts is applied to the silenoid, but the valve won't switch from heating to cooling, the reversing valve is bad. Finally, sometimes you'll have a situation where the slider is stuck in the middle or leaking high side refrigerant to the low side. This can cause the compressor to run hot, increasing the amp draw to above its RLA and tripping the internal overload protection switch of the compressor. I explained what that is in my compressor video, but your such-and-line pressures will be higher than normal and your high side pressures will be lower than normal. This alone can make you think that you have a bad compressor, but a couple more checks will help you complete this diagnosis. You'll also read that the suction line entering and leaving the reversing valve will have a significant difference in temperature by feel or an actual temperature probe measurement. Record the temperatures of the line approximately 6 inches away from the body and see if there's heat gain or loss. In the cooling mode, take the temperature reading of the discharge line coming in from the top and the line going to the outdoor coil. Take another set of readings at the constant suction line and the line leading to the indoor coil. The temperature difference between the readings at the discharge line and the line going to the outdoor coil should be 4 degrees or lower. The temperature difference between the readings at the constant suction line and the line going to the indoor coil should also be 4 degrees or lower. The temperature difference is due to heat transfer as refrigerant passes through the reversing valve. Under extremely high outdoor temperatures, the difference can be as high as 7 degrees, and there's nothing wrong with that reversing valve. Just like with control boards on a furnace, if the board is giving proper voltage to the reversing valve, silenoid, and the slide isn't working, it's probably not the board. If the board isn't giving proper voltage, then it's the board or something else upstream of it. You can see reversing valves aren't that hard, so the next time you walk up on a failed heat pump and it starts pointing towards the reversing valve, you can always refer back to this video. If this is your first time watching our channel, please click subscribe down here on the bottom right, and if you click that little bell next to it, you'll be notified of all of our videos as they come out. Thanks so much for watching and we'll see you on the next video. If you're watching Fox Family Heating and Air, don't forget to subscribe, and check out more of our videos by clicking on the right side of the screen.