Heat Pump Blowing Hot Air In Cool Mode? (Fix It Now!)

Ryan Womeldorf
by Ryan Womeldorf

A heat pump can be an efficient way of delivering hot or cool air into your home depending on the time of year and the temperature outside. When the temperatures soar in the summer, a heat pump that blows hot air is doing you no favors.

Understanding why your heat pump is blowing hot air, even when in cool mode, is important. It could be due to refrigerant leaks, a dirty or clogged air filter, dirty coils, or even a failed valve. You will need to troubleshoot the issue or have a certified HVAC technician come out to check the issue.

Do You Need Heat Pump Repair or Service?

Get free, zero-commitment quotes from pro contractors near you.

Why Is My Heat Pump Blowing Hot Air in Cool Mode?

If it’s a warm day and your heat pump is not cooperating and is actually circulating hot air throughout your home, here are the seven top reasons that this might be happening:

1. Thermostat Set Incorrectly

More often than not, issues with heating and cooling revolve around an improperly programmed thermostat. When the thermostat is set to either heat or fan-only in the summer, the heat pump will blow warm air at best.

Thermostat on cool mode. Let’s say that you get over to the thermostat and notice that it is indeed set to cool mode. When set in cool mode, you should be getting cool air, right? Well, when warm air is still blowing in, it could be indicative that the thermostat is broken.

If your thermostat is powered by batteries, you can try to change the batteries first. Or, if you notice that the screen on your thermostat is blank, you should check if one of your breakers has tripped. Worst case scenario is that your thermostat is defective and will need to be replaced entirely.

If your thermostat is an older model, you should strongly consider replacing it altogether. They are relatively cheap – as low as $20 – but can be quite expensive the fancier you get. There are plenty of thermostat buying guides out there that can help you make the right choice. If your thermostat is newer, then it is probably one of the issues later on down the list.

2. Dirty or Clogged Air Filter

The air filter in your heat pump can cause major issues. The filter is meant to keep airflow consistent and provide a cleaner, better air quality. Over time, the air filter will become clogged by contaminants and dust in the air, reducing its effectiveness.

When the air filter is dirty, airflow is restricted. Even if your heat pump is working properly to cool the air, the air may not be able to pass through the ductwork and into your home. So, while it may seem like a greater issue, cleaning or changing the filter may be the right idea.

Cleaning your air filter. In a pinch, you can clean the air filter. Keep in mind that the overall quality and integrity of the air filter can be compromised over time. So, while it may be cheaper and quicker to clean the filter, you can only do it so much.

Use a soft brush to remove any thick layers of debris. So long as the dust is not packed on tightly, you can also give it a gentle shake or tap to get most of the dust and debris off, too.

The best course of action is to replace the air filter. Monthly is the best bet though in most cases you can extend it to bi-monthly. Keep in mind that changing out your air filter monthly will lead to increased costs in the long-term.

3. Low Refrigerant

Perhaps the most common mechanical reason for your heat pump blowing hot air is low refrigerant. The vast majority of the time, low refrigerant is the result of a leak somewhere in the system.

The refrigerant in the heat pump captures the heat inside your home (or outside in the winter) through the system’s indoor coil. The refrigerant line then carries the hot refrigerant outside in the summer, where it goes into the outdoor coil. Finally, the heat gets released and dispersed through the heat pump fan.

Refrigerant Leak. When the charge is low, there isn’t the requisite amount of refrigerant available to do the job. That means no heating or cooling at all. Unfortunately, a license is required to handle refrigerants as well as the special equipment needed to read charges.

Refrigerant leaks can be quite costly to repair. The tech will use a sensor to locate the source of the leak. Should it be at a fitting, the repair could be as little as $200-$250. But if the coil is leaking, replacing it is much more expensive. You can safely expect to pay $600 to more than $2,000.

4. Dirty Heat Pump Coil

Because it is an outdoor unit, the heat pump is subject to different levels of dirt and debris. Dust and dirt are still issues, but there is also grass clippings, pet hair, and dozens of other types of contaminants to contend with.

The indoor coil needs to be clean in order to collect heat. Likewise, the outdoor coil has to be clean to disperse that heat effectively. When it is clogged or dirty with debris, it won’t be able to do that job effectively.

  • Cleaning an outdoor coil. The good thing about an outdoor pump coil is that it can be done using a hose. Just make sure that you don’t use a pressure washer as the extra pressure can damage various components. Use the hose to rinse away any loose debris. For more stubborn debris and dirt, use a light bristle brush to break things up.
  • Cleaning an indoor coil. These are more difficult to clean because they are more difficult to get to. Generally speaking, unless you are on a tight budget, it is best left to an HVAC technician. Services should range between $75 and $200 depending on the service that you use.

There are ways to clean the indoor coil yourself, though. Follow the same protocols: gentle brushes to perform the heavy cleaning, rinsing away the debris when finished.

5. Frosted Indoor Coil

When the system is set to Cool mode, the coil from the furnace or air handler gets very cold. Add in the fact that it condenses moisture from the air in an effort to dehumidify your home and you’ve got an interesting combination. After all, condensation plus cold temperatures equal frost.

That build-up is what prevents heat from gathering. As a result, the heat pump will blow out hot air instead of cool air. Some heat pumps reverse the flow of refrigerant to pick up some outside heat, defrosting the coil in the process.

How to fix the frost issue. Be prepared to allow your system 30-45 minutes of downtime. Let the coil take on warm air for that time. Then, turn the system to fan mode. Fan mode pulls air from your house into the system and over the coil. That air should be warm enough to defrost the indoor coil.

6. Valve Failure

There are a number of valves within your heat pump system. Those valves are meant to direct the flow of refrigerant through your heat pump system. There is the thermal expansion valve (TXV), the reversing valve, and valves that control the flow of the refrigerant.

What you may not have realized is that heat pumps don’t actually make heat. All they do is move it around. Those reversing valves change the flow of refrigerant to carry out or collect heat (for air conditioning) or flip it around for heating mode.

Valve replacement. Each of these valves are supported by solenoids, which are electric components. When the valves (or the solenoids) get damaged, the valves won’t work properly. And when that happens, the valve needs to be replaced.

The most difficult part is diagnosing the problem. More importantly, replacing a valve usually means having to add refrigerant to the heat pump system. And that requires a refrigerant license as well as pressure testing.

7. Duct Leak

Air ducts, especially if they’re older, are prone to leaking. When your ductwork has sprung a leak, it won’t be able to effectively distribute the air through your home’s vents. This can cause your home to feel warm in some areas. If you suspect that you may have a duct leak, you’ll want to contact a professional heating and cooling company.

They’ll be able to perform a detailed analysis of your ductwork to spot the source of the leak and correct it. By finding the source of lost energy, you will save money in the process.

Do You Need Heat Pump Repair or Service?

Get free, zero-commitment quotes from pro contractors near you.

Repair or Replace the Heat Pump?

There are a number of factors that will determine whether you should repair the heat pump or replace it entirely. It comes down to the age of the heat pump, the cost of the repair, and whether or not your system is under warranty.

  • Warranty. If your system is under warranty, you will most likely get a repair. After all, a warranty is meant to cover a variety of repair issues and will save you a ton of money on repair costs over the life of the warranty.
  • Cost of repair. The cost of the repair can really be the most important aspect. If your entire system runs about $4,000, you probably don’t want to spend half of that on repairs. Also, if your system has the need for frequent repairing, it might be worth considering replacing the entire thing.
  • Age of the system. How old is your heat pump? That is another consideration to make. If your system is a decade or more in age, and it has had several repair issues already, it might be more ideal to replace the system. Granted, paying $3,000-$6,000 is never an attractive prospect, but it might save you time, money, and hassle in the long run.
  • Get estimates. When in doubt, get estimates. It may seem more frugal to get a repair done but an estimate can give you better clarity. Not only that, having an HVAC technician come out to assess the condition of your heat pump will let you know if there are other underlying issues.

Related Questions

How do I know that my heat pump is low on refrigerant?

The level or charge of refrigerant should not decrease over time. Though, leaks can cause your heat pump to lose refrigerant. If your heat pump is leaking, it’s likely you’ll have other problems arise as well.Since the purpose of refrigerant is heat absorption, a lack of refrigerant will hinder the coil’s ability to absorb heat and, thus, cause the moisture on the coil to freeze. Low refrigerant will also place unnecessary strain on the heat pumps components, resulting in inefficient performance overall.

Why is my heat pump not cooling my home?

If your heat pump isn’t cooling your home or it’s doing a poor job, start with your thermostat. Make sure that the thermostat is set to cool and at least two degrees below the current temperature. If it is set correctly, then make sure that your outdoor unit’s fan is running.If it isn’t running, there may be a lack of power to the air conditioner, an issue with the wiring somewhere between the thermostat and outdoor unit, or a bad thermostat.

Ryan Womeldorf
Ryan Womeldorf

Ryan Womeldorf has more than a decade of experience writing. He loves to blog about construction, plumbing, and other home topics. Ryan also loves hockey and a lifelong Buffalo sports fan.

More by Ryan Womeldorf