Why is my Heat Pump Blowing Cold Air? | Richard, love your website!! I used a few months ago to install a new thermostat, and you cleared some things up with the thermostat wiring colors I had problems trying to figure out. Thanks!!

Now I just turned on my heat pump the other night when it was cold outside. I wanted to warm the house up a bit since, in the daytime, it gets back up to reasonable temperatures. The heat pump is blowing cold air when the thermostat was set to heat.

I am just wondering if I hooked something wrong hooking up the thermostat, or perhaps I have a problem with the heat pump and need to call someone out to fix the problem. Regarding your reply to my original comment, I turned the thermostat up to 80° F. when the house temperature was 72°, and the thermostat was set to heat.

The supply vents did start blowing warm air. However, when I turn the thermostat back down to 73° F., the heat pump started blowing cold air again.

I look forward to your answer. Thanks again for all your help!! Rebecca.

Heat Pump Blowing Cold Air | Refrigeration Heating Troubleshooting

Rebecca, thank you for your kind comments about the site!! I do work hard on it and try to answer everyone, but sometimes it is difficult for various reasons. Now, to answer your question: Since you ran the little test I had you do, we know your auxiliary heating or backup heat is working. That means you have a problem with the refrigeration portion of your heat pump.

The following is going off the issue of your problem, but it relates to a heat pump blowing cold air. Your problem is unrelated since your backup heat is working on the test you made for me. Thanks!! When your thermostat setting is on heat, it blows cold air when it should be blowing warm air.

Of course, when in heat mode, you get warm air and not cold air. That’s a no-brainer. Let’s explore this problem and break it apart because we want your heat pump to blow warm air when in heating mode. Here are the possibilities:

• Defrost Problem
• Refrigeration Problem - yes heat pumps use the refrigeration cycle to provide heat in the winter
• Thermostat or Control Problem
• A Problem in the Condensing Unit

Let’s explore each possible heat pump blowing cold air problem below.

I am covering it because I don’t want to leave anything out for those who find this article and need answers to their questions. We know your backup heat works just fine, so please ignore the first part of my answer. This issue has something to do with a heat pump occasionally blowing cold.

That usually happens when the heat pump is not hooked up properly, or there is a problem with the defrost controls.

Heat Pump Blowing Cold Air Troubleshooting Matrix

My Heat Pump Occasionally Blows Cold Air On Heat Setting | Heat Pump Blowing Cold Air

Goodman Heat Pump Defrost Control

It happens when the heat pump shifts into defrost mode. Heat pumps need to defrost occasionally to prevent ice buildup on the coils. A timer built into the defrost control board initiates defrost. It is a defrost method used by many conventional HVAC manufacturers. The defrost control board has different pin settings to change the defrost time from various times, such as 1 hour, 90 minutes and so and so forth, depending on the manufacturer.

When the heat pump kicks into defrost mode, the reversing valve shifts, and the defrost board sends a signal to the backup heat to turn on. Why do you want your backup heat on when the heat pump is in defrost mode?

Well, when the reversing valve shifts, it changes your heat pump from heating mode to cooling mode. That creates heat in the coils of the condenser. The heat defrosts the coils. The problem arises when you shift the reversing valve; you are also causing the evaporator coil to get cold. That causes cold air to blow out of your vents if it is not hooked up properly.

Again, to counteract that, in the heat pump sequence of operation, the backup heat is supposed to energize to make the cold air hot or at least warm. That prevents your heat pump from blowing cold air out of the vents. I picked up a whole housing subdivision of customers because the installation contractor did not hook this up properly. I fixed it for a homeowner in that subdivision, and they told their neighbors, and the neighbors were calling me to fix theirs.

Refrigeration Problems for Heat Pumps | Heat Pump Blowing Cold Air

Heat pumps use the process of refrigeration to move heat. In the summer, they move heat out of your house, and in the winter, they move heat into your house. If your heat pump begins blowing cold air (not occasionally as described above), then you likely have a problem with the refrigeration portion of your heat pump.

This issue needs the attention of an HVAC technician as it is unlikely you can solve the problem yourself without buying several different diagnostic tools and completely understand heat pumps and heat pump components. Let’s take it from the top:

Heat Pump Thermostat | Heat Pump Blowing Cold Air

First, make sure your thermostat is set to heat, and you have increased the setpoint for heat. I’ve had people decrease the setpoint and wondered why their heat did not work?? Anyhow, make sure you only set 1° above the house temperature. Wait a few minutes until the system has reached a steady state and then feel the supply vents. Is the temperature warm or hot? No. Then keep reading.

Now turn the thermostat up at least 5° above the house temperature. Feel the vents again after a few minutes? Is the air coming from the vents hot or warm? No. Keep reading. Has anyone changed the thermostat recently?

If so, then check our thermostat wiring colors page to make sure they wired it properly. If not, then keep reading. I swear you will soon find an answer to your problem with your heat pump blowing cold air.

The Heat Pump Condensing Unit

Problems that will cause your heat pump to blow cold air in the winter include:

• Your heat pump condenser tripped the breaker, so it’s blowing cold air. That includes electrical problems such as a bad compressor contactor.
• The reversing valve not shifting properly. Reversing valves for most heat pumps only shift for cooling. Rheem and Ruud shift the reversing valve for heating. I disagree with that, but Rheem and Ruud do it their way, so who am I to say that a reversing valve if it fails, should fail to heat because heat is so much more important than cooling.
• Your heat pump has a refrigerant leak (Freon leak as some people call it) that needs a leak check to find and repair the leak. Fixing a refrigerant leak is always recommended; however, some people call a contractor, and the contractor refills the system until you need it again. I recommend you fix the refrigerant leak.
• Something could be wrong with the compressor. It could have an electrical problem, or it could have a mechanical issue. Either way, a professional should troubleshoot the compressor problem and fix it. Hopefully, this is not your problem.

Delta T for Heat Pumps and the Human Factor

Lastly, to rule out any subjective factors related to what you think is warm or cold (it’s different for everyone based on perception), you can do a delta “T” reading. Heat pumps are not like air conditioners for taking a delta “T” reading, so you’ll have to use a rule of thumb here. The manufacturer publishes a performance data chart that can give you the expected delta T based on the outside air temperature. Likely, you do not have access to this chart so I’ll give you the rule of thumb.

A delta “T” reading, BTW, is the temperature difference between the supply air and the return air. Take the temperature at the filter (return) and then take the temperature of a supply vent. Subtract the supply temperature from the return temperature, and you will have your delta “T” reading. The rule of thumb says this temperature difference should be between ~10°F and ~30°F depending on the outside air temperature. If the outside air temperature is freezing the delta T will be lower.

Conclusion

Heat Pump Blowing Cold Air | Refrigeration Heating Troubleshooting

There are other reasons your heat pump could be blowing cold air instead of heat, but those are the basics. Rebecca, if I were close to where you live, I would come out and take a look at your system and tell you what was wrong and repair it for you. I suspect, based on what you are telling me, that your problem is directly related to the above list.

Either way, call your local contractor and have them take a look and fix it for you. Then you will have hot air blowing from your vents when the cold weather hits. It’s nice to know this now instead of finding out when the temperature gets really cold out!! Good luck!!

Update: Rebecca sent me an email after the contractor left her house. The heat pump is working fine. Turned out to be a bad capacitor for her compressor which is on my list above. She did a fine job installing her new thermostat, and everything works well now. And the blown capacitor has nothing to do with changing her thermostat.

Glad I could help!! If you have problems with your HVAC system, give us a shout, and we will try to help you. You can use our uploader (on the menu to the right) to send us photos and a description of the problem. Rebecca used the uploader to send us some pics of her thermostat wiring, and it worked great!!

Why is my Heat Pump Blowing Cold Air?

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Resource: The Home Comfort Book: The ultimate guide to creating a comfortable, healthy, long lasting, and efficient home