Heat Pump Reversing Valve Basics: How One Part Lets Your System Heat And Cool

Heat pumps are becoming more popular every year around Rancho Cordova and the greater Sacramento area. With energy costs rising and efficiency standards getting stricter in 2025, many homeowners are looking at air source heat pumps as a smart way to handle both cooling and heating with a single system. One small but very important part makes that possible: the reversing valve.

If you have ever wondered how the same outdoor unit can blow cool air in July and warm air in January, or why your heat pump sometimes ices up on cold mornings, understanding the reversing valve will help everything make more sense. This article walks you through what a heat pump is, how the reversing valve and its solenoid work, what happens in cooling and heating modes, and common issues that our technicians see in Sacramento homes.

When you understand the basics, you will be better prepared to recognize problems early and know when it is time to schedule a professional visit with a trusted local company like Fox Family Heating and Air Conditioning.

What Is A Heat Pump?

An air source heat pump looks a lot like a standard air conditioner, and in cooling mode, it operates the same way. The system uses refrigerant to move heat, not to create it. In the cooling season, the indoor coil is the cold evaporator coil, and the outdoor coil is the hot condenser coil. Heat is absorbed from the air inside your home and rejected to the outside air.

The difference shows up when the weather cools down. Instead of firing a burner like a gas furnace, a heat pump can flip its operation so that the indoor coil becomes the hot coil and the outdoor coil becomes the cold coil. The system pulls heat energy from the outside air and brings it indoors. Even when the outside air feels cold to you, there is still usable heat in that air that a properly sized heat pump can capture.

Modern heat pumps are very efficient in mild climates like the Sacramento Valley. With current federal standards, new heat pumps are rated using SEER2 for cooling efficiency and HSPF2 for heating efficiency. As of late 2024, the U.S. Department of Energy minimum standard for most new split-system air source heat pumps is 14.3 SEER2 for cooling and 7.5 HSPF2 for heating. Many systems go well beyond those minimums.

Whether your system uses R-410A or one of the newer refrigerants such as R-454B, the overall heat pump cycle is the same. The reversing valve is the traffic director that sends refrigerant the right way for the mode you need.

How The Reversing Valve Works

You can think of the reversing valve as a four-way intersection for refrigerant. It has:

• One connection from the compressor discharge line
• One connection to the compressor suction line
• One connection to the indoor coil
• One connection to the outdoor coil

Inside the valve, a sliding element connects these ports in different ways depending on whether the system is in heating or cooling mode. That slide is moved by pressure differences created inside the valve and controlled by a small pilot section and a solenoid coil.

On most residential systems, the valve sits in its default position when there is no electrical signal going to the solenoid. For most equipment in our area, the default position is heating mode. That way, if something fails electrically, the system is more likely to still provide heat, which is considered more critical than cooling in many parts of the country.

When the thermostat and the outdoor control board call for cooling, the board sends a 24-volt signal to the solenoid on the reversing valve. That energized solenoid shifts the pilot valve, which changes the refrigerant pressures on each side of the internal slide. With enough pressure difference, the slide moves to its cooling position, and the refrigerant paths are swapped.

From your viewpoint as a homeowner, this all happens quietly in the outdoor unit. You do not see the slide move, but you notice the results inside when the air from your vents changes from warm to cool or the other way around.

Cooling Mode: Refrigerant Flow Direction

In cooling mode, the reversing valve directs refrigerant so that the indoor coil acts as the cold evaporator coil and the outdoor coil acts as the hot condenser coil.

The general refrigerant path in cooling looks like this:

1. The compressor pushes hot, high-pressure gas out of its discharge line.
2. The gas enters the reversing valve and is routed to the outdoor coil.
3. As outdoor air blows across that coil, heat is removed from the refrigerant, and it condenses into a warm liquid.
4. The liquid passes through the metering device and expands, dropping in pressure and temperature.
5. The cold, low-pressure refrigerant enters the indoor coil, where it absorbs heat from the air passing over the coil.
6. The refrigerant evaporates back into a low-pressure gas, travels back through the reversing valve to the compressor suction line, and the cycle repeats.

When everything is operating correctly in cooling mode, you feel cool air coming from your supply registers, and the outdoor unit exhausts warm air as it rejects heat from your home into the Sacramento summer air.

Heating Mode: Refrigerant Flow Reversed

In heating mode, the reversing valve does its main job. When the system switches to heating, the valve changes the paths inside so that the indoor and outdoor coils trade roles.

The refrigerant path in heating mode looks like this:

1. The compressor still pushes hot, high-pressure gas out of its discharge line.
2. This time, the reversing valve routes that hot gas toward the indoor coil.
3. The indoor coil becomes the condenser. As your furnace or air handler blower moves air across the coil, heat from the refrigerant is released into your ductwork and then into the rooms of your home.
4. The refrigerant leaves the indoor coil as a warm liquid, passes through the metering device, and expands into a cold, low-pressure mixture.
5. That cold refrigerant flows to the outdoor coil, which now acts as the evaporator. The coil absorbs heat from the outside air, even when temperatures are close to freezing.
6. The refrigerant leaves the outdoor coil as a low-pressure gas, travels back through the reversing valve to the compressor suction line, and the cycle continues.

Because the outdoor coil is colder than the outside air in heating mode, moisture in the air can frost up on that coil. This is normal to a point and is one reason the defrost cycle is so important on heat pumps.

Why Heat Pumps Work Well In The Sacramento Area

The Sacramento Valley is an ideal region for heat pumps because our winters are relatively mild. Typical January lows are around the upper 30s, and true freeze events are not very common. That means there is plenty of heat energy in the outside air for a properly sized heat pump to capture.

In summer, we see many days at or above 100 degrees, so you still need strong cooling performance. Modern air source heat pumps are designed to handle both extremes, especially when installed and set up correctly for our climate. With SEER2 and HSPF2 ratings that keep improving year after year, many homeowners are finding that a heat pump can reduce overall energy use compared to running a separate air conditioner and gas furnace.

As of late 2024, federal tax credits for qualifying high-efficiency heat pumps are available under the Energy Efficient Home Improvement Credit in the federal tax code. Many utilities, including SMUD and PG&E in Northern California, have also offered rebates for qualifying heat pump installations. Because tax laws and rebate programs change frequently, it is important to confirm current details with the Internal Revenue Service and your local utility before making a purchase decision.

For the latest federal requirements on heat pump efficiency, refrigerant rules, and tax credits, review information from the U.S. Department of Energy, the U.S. Environmental Protection Agency, and the Internal Revenue Service before you decide on new equipment.

If you are thinking about replacing your system and want to know whether a heat pump is a good fit for your home in Rancho Cordova or Sacramento, our team can help you compare options and understand the long-term costs.

The Role Of The Solenoid On The Reversing Valve

The solenoid is the electrical part that tells the reversing valve when to change position. It is a small coil of wire that becomes magnetic when energized by 24 volts from the outdoor control board.

Here is how it fits into the system:

1. Your thermostat calls for heating or cooling.
2. The control board decides whether the system should be in heating mode or cooling mode based on that call.
3. For most brands, the board sends 24 volts to the solenoid when cooling is needed and removes that power when heating is needed.
4. The magnetic force from the energized solenoid shifts the pilot section of the reversing valve, which changes the internal pressure balance and moves the slide to the correct position.

If the solenoid fails or loses power, the valve can stay in the wrong position or refuse to shift at all. From inside the home, this might look like the system staying in cooling when you want heating or blowing lukewarm air in either mode.

Because the solenoid is an electrical component, diagnosing it correctly involves checking voltage and resistance with a meter. That is work best left to a trained HVAC technician who can do it safely and accurately.

Defrost Cycle Basics

Whenever a heat pump is in heating mode, the outdoor coil is operating at a temperature below the outdoor air. On cold, damp days around Sacramento, moisture in the air freezes on that coil and creates a layer of frost or ice. A light coating is normal, but too much ice blocks airflow and reduces efficiency.

To prevent this, heat pumps use a defrost cycle controlled by the outdoor board. Here is what typically happens during defrost:

1. The control board monitors outdoor coil temperature and run time.
2. When conditions indicate that the coil has frosted, the board temporarily shifts the system into a modified cooling mode by using the reversing valve.
3. The outdoor fan usually shuts off, and the hot refrigerant helps melt the ice off the coil.
4. You might feel slightly cooler air coming from your vents for a short time, because the system is not delivering full heating during defrost.
5. Once the coil is clear, the board switches the valve back to normal heating mode and restores regular operation.

If the defrost cycle stops working correctly, you may notice heavy ice buildup on the outdoor unit, loud fan noises from hitting ice, or very poor heating performance. Since the defrost board, sensors, and reversing valve all work together, a qualified technician should diagnose this type of problem.

Common Reversing Valve Problems

Reversing valves are heavy-duty parts, but they can still fail. Most issues fall into one of three categories: electrical problems, mechanical problems inside the valve, or problems elsewhere in the system that affect how the valve works.

Here are some of the more common symptoms homeowners notice:

• The heat pump cools fine in summer but blows cool or lukewarm air in heating mode.
• The system heats but will not switch into cooling when you adjust the thermostat.
• You hear the outdoor unit running, but indoor temperatures do not change much in either mode.
• The outdoor unit runs very hot, trips safety devices, or seems to short-cycle.

Some specific issues our technicians see include:

1. Failed solenoid coil
   The solenoid can burn out over time, especially if it overheats or has been energized and de-energized thousands of times. When this happens, the valve may stay stuck in one position because it never gets a proper switching signal.
2. Stuck internal slide
   The sliding part inside the valve can stick because of contamination, overheating, or damage from a past compressor failure. In some cases, switching the thermostat from heating to cooling and back a few times while the system is running can generate enough pressure difference to free the slide, but a truly stuck valve usually has to be replaced.
3. Valve is leaking between the high and low sides
   A worn or damaged valve can allow high-pressure and low-pressure sides of the system to mix inside the valve. This raises suction pressure, lowers discharge pressure, and can cause the compressor to run hot and pull higher amps. From a homeowner’s perspective, this often feels like very weak heating or cooling, even though the outdoor unit seems to be running normally.
4. Control board or wiring problems
   Sometimes the valve itself is fine, but the control board never sends the correct 24-volt signal, or a wiring issue prevents the solenoid from energizing. That is why technicians always check the whole control circuit during a service call.

Because the reversing valve is brazed into the refrigerant lines, replacing it is a significant repair. The system has to be recovered, opened, and then recharged to the correct level afterward. This is not a do-it-yourself project and should always be handled by a licensed HVAC professional.

Heat Pump Vs Furnace For Sacramento Homeowners

Many homeowners in Rancho Cordova and Sacramento want to know whether they should keep a gas furnace, go all in on a heat pump, or use a dual fuel setup.

Here are a few points to consider:

• Comfort in mild winters
  Because our winter temperatures are not extremely cold, a properly sized heat pump can usually handle most of the heating load without needing backup heat very often. That makes it a strong option for comfort and efficiency.
• Energy source and costs
  A gas furnace relies on natural gas, while a heat pump runs entirely on electricity. If you already have solar panels or plan to install them, a heat pump can make even more sense because you are using more of your solar production to heat and cool your home.
• Efficiency ratings
  High-efficiency gas furnaces can reach very high AFUE ratings, but only for heating. A modern heat pump offers high efficiency in both cooling and heating seasons, which can balance your utility costs across the year.
• Environmental impact
  Many homeowners are interested in reducing their use of fossil fuels. Switching to a heat pump can be one step in that direction, especially as the electric grid continues to add more renewable energy sources.

The right choice for your home depends on your budget, the age and condition of your current equipment, and how you use your system. Our technicians can help you compare a high-efficiency heat pump with furnace options and explain how the reversing valve and other components will affect your comfort over the life of the system.

When To Call A Professional

Heat pumps are safe and reliable when they are installed and maintained correctly, but the reversing valve and its controls are not simple parts. There are a few basic checks you can do as a homeowner, such as:

1. Make sure your thermostat is set to the correct mode and temperature.
2. Checking that the outdoor unit is running when the system calls for heating or cooling.
3. Changing your air filter regularly so airflow is not restricted.
4. Visually check the outdoor unit for heavy ice buildup or damage.

If you notice any of the following, it is time to schedule service:

• The system stays stuck in heating or cooling mode no matter what you do at the thermostat.
• You hear the outdoor unit running, but the air coming from your vents never feels truly warm or cool.
• There is heavy ice or frost on the outdoor unit that does not clear on its own.
• Your utility bills are much higher than normal for the season.

An experienced technician will check electrical signals, system pressures, temperature differences, and the condition of the reversing valve and other key components. They can tell you whether a repair is possible or whether a larger replacement should be considered.

If you are concerned about your heat pump, call Fox Family Heating and Air Conditioning at 916-877-1577 or schedule your appointment online. Our team works on heat pumps every day across Rancho Cordova, Sacramento, and the surrounding communities.

Conclusion

The reversing valve is a small part with a big job. Changing the direction of refrigerant flow allows your heat pump to keep you cool in triple-digit Sacramento summers and warm during our chilly winter nights. When the valve, solenoid, and defrost controls are working together properly, you enjoy efficient, reliable comfort in every season.

If you understand the basics of how your heat pump works and recognize the early signs of trouble, you can address issues before they turn into breakdowns on the hottest or coldest days of the year. Regular maintenance, proper diagnostics, and professional repairs will help your system last longer and perform better.

Fox Family Heating and Air Conditioning serves Rancho Cordova, Sacramento, and Northern California. If you need help with your heat pump or reversing valve, give us a call!