New Honeywell Thermostat Blowing Hot Air On Cool [Solved]

Experiencing the frustration of your Honeywell thermostat blowing hot air when it should be cooling things down? Don’t worry, you’re not alone. 

Let’s get to the bottom of this issue with a quick troubleshooting guide.

Table of Contents

Several factors could be causing your thermostat to misbehave:

Faulty or incompatible thermostat: Ensure your thermostat is the right match for your system.

Stuck Changeover valve: A sticky valve might prevent the switch from cooling to heating.

AC Condenser unit malfunction: Check if your condenser unit performs correctly.

Thermostat wiring issues: Faulty wiring could be the culprit; inspect and fix if necessary.

Defective circuit control board: A malfunctioning board might be confusing temperature control.

Incorrect thermostat settings: Double-check your settings to make sure they align with your cooling needs.

O/B terminal not connected: Ensure the O/B terminal is connected correctly for seamless operation.

Conventional heating system: If you have traditional heating, not a heat pump, this could affect your thermostat’s behavior.

Before diving into the specifics of our troubleshooting guide, it’s essential to note that this advice applies to a broad range of thermostat brands, including Honeywell, Sensi, Ecobee, Google Nest, and others.

Reasons A Honeywell Thermostat is Blowing Hot Air on Cool

Possible CauseMain Fixes
Incorrect thermostat settingsAdjust the thermostat to cool
Bad thermostat wiringCorrect thermostat wiring
Conventional heating systemUpgrade to an air conditioner or heat pump
AC Condenser unit not workingTurn on the condenser unit
Stuck Changeover valveReplace the changeover valve
Defective circuit control boardReplace the circuit control board
Defective or incompatible thermostatReplace the thermostat
O/B terminal not connectedConnect the wire to the terminal

1) Incorrect thermostat settings

1) Incorrect thermostat settings

The first thing you want to address when you notice your Honeywell thermostat blowing hot air on the cool setting is checking and correcting the thermostat settings. Incorrect settings are the primary culprits for this cooling and heating hiccup. It may sound like a no-brainer, but many homeowners need to remember to switch between heating and cooling on their thermostats.

Changing the orientation is crucial if you’re using a Nest thermostat. Here’s what you need to do:

Ensure you’re using a heat pump for temperature control.

For Nest Learning or Nest E:

Navigate to your thermostat settings and choose ‘equipment.’

Select ‘heat pump.’ You’ll find a switch button for toggling between O and B, with the default setting being O.

If option O is highlighted, switch to B. Conversely, if B is highlighted, select O.

Now, put the system to the test by calling for cooling.

If your system starts cooling, congratulations! You’ve just fixed the problem. If not, let’s move on to the next steps in our troubleshooting journey.

Read also: Honeywell Thermostat From Celsius To Fahrenheit

2) OB terminal not connected

If, after you’ve tackled the first troubleshooting step and corrected your Honeywell thermostat’s orientation settings, the issue persists with the system heating on the cool ground, it’s likely a wiring problem at the O/B terminal. It’s worth noting that conventional heating shouldn’t have a wire in the O/B terminal.

To check the O/B terminal wiring:

Ensure you turn off power to your HVAC system using the switch at the main circuit breaker or both.

Carefully detach the thermostat display from the wall and examine the wire connected to the O/B terminal. Look for any corrosion or looseness. Remove the wire and strip it enough to ensure a proper connection with the terminal.

Inspect for any signs of wear or damage on the wire. Ensuring the wire is in good condition for effective connection is essential.

Reinsert the wire into the connector and reattach the thermostat display.

Power on your system and test if the cooling function is working correctly.

Pro Tip: Regularly inspect and maintain your thermostat wiring to prevent potential issues. Well-maintained connections contribute to a more efficient HVAC system. 🔧

3) Bad thermostat wiring

Incorrect thermostat wiring might be the culprit if your Honeywell thermostat is blowing hot air when set to cool. Aside from inspecting the wire connected to the O/B terminal, it’s crucial to ensure all other cables are correctly mapped to their respective terminals.

This is especially important if you recently switched from a Honeywell thermostat to a Nest thermostat or between different brands.

Verify that there are no loose wires in the thermostat.

For Honeywell thermostats, check if separate wires connect to Rc (power for cooling) and RH (power for heating). If not, insert a jumper between the two terminals and test for cooling.

Note: Before opening the thermostat, turn off the power for safety.

Quick Wiring Color Code for Honeywell Thermostat:

Thermostat WireTerminal
Aux / W2Heat Stage 2 (Heating)
EEmergency Heat
L/A – AInput for heat pump fault
O/BReversing valve for Heat Pump systems
R24vac (Heating transformer)
SIndoor and Outdoor Wired Sensors
UHumidifier, Dehumidifier, or Ventilator control
WHeat Stage 1 (Heating)
YCompressor Stage 1 (Cooling)
Y2Compressor Stage 2 (Cooling)

Pro Tip: When dealing with thermostat wiring, consult the color codes and specific instructions for your model to ensure accurate and efficient connections. 🌈

4) You don’t have a heat pump

If your Honeywell thermostat is blowing hot air on the cool setting, it could be because you don’t have a heat pump. A heat pump operates by providing heat when needed and cooling when necessary.

If you only have a furnace or conventional heating, setting the thermostat to cool won’t effectively cool your home. Try turning on your system to heat to check if you have a heat pump. You might not have a heat pump if the outdoor unit doesn’t activate.

For a more precise confirmation, manually check the label on your outdoor condenser unit. In most cases, this information is available there.

If you believe you have a heat pump, but the thermostat continues blowing hot air in cool mode, ensure the condenser unit functions correctly.

Expert Tip: Understanding your HVAC system type is crucial for effective thermostat usage. Confirm your system’s specifications to optimize heating and cooling settings.

Read also: How to Reset Honeywell Thermostat Without a Reset Button?

5) The AC condenser unit not working

The AC condenser unit not working

The condenser unit plays a crucial role in the cooling process as it is where the condensation of freon occurs. This is the stage where the heat from your home is expelled outside, aided by a condenser fan.

If the condenser is inactive or lacks a power supply, cooling within your home won’t happen.

Check for a power supply if your outdoor condenser unit fails to turn on when you adjust your thermostat. Head to the circuit breaker and inspect the switch labeled air conditioner. If it’s tripped, reset it to the original position and see if your condenser resumes operation.

At times, a defective compressor capacitor can be an issue. In such cases, replacement is necessary.

Troubleshooting an AC Compressor That Won’t Turn On:

Possible CauseMain Fixes
No power/tripped breaker switchTurn on tripped circuit breaker
Defective capacitorReplace capacitor
Stuck contactor in the off positionClean or replace contactor
Defective fan motorReplace fan motor

Pro Tip: Regularly check your outdoor condenser unit for any signs of wear or malfunction. Keeping it in good condition ensures efficient cooling and extends the lifespan of your HVAC system. 

6) A stuck changeover valves

A stuck reversing valve in a heat pump could be why your Honeywell thermostat blows hot air on the cool setting. Let’s delve into how a reversing valve functions to grasp this issue better.

The reversing valve on a heat pump facilitates the switch in the direction of the refrigerant flow, enabling the heat pump to alternate between cooling and heating. In essence, it reverses the flow of freon, allowing the heat pump to function as both an air conditioner and a heater.

Over time and due to various factors, a reversing valve may become stuck in the heat position, leading to the thermostat blowing hot air when set to cool.

Another common factor contributing to a stuck reversing valve is a broken solenoid. The solenoid is responsible for transitioning between modes, and if it’s broken, the reversing valve can get stuck.

While a solenoid is inexpensive, its replacement should be cautiously approached. If you’re familiar with the task, you can replace it affordably. However, for those unsure, it’s advisable to seek professional assistance.

Troubleshooting a Stuck Reverse Valve:

Possible CauseMain Fix
Aged reversing valveReplace reversing valve
Broken solenoidReplace solenoid

Pro Tip: Regular maintenance can help identify potential issues with the reversing valve early on, preventing malfunctions and ensuring your heat pump operates efficiently. 🔄❄️🔧

7) A defective circuit control board

The circuit control board (CCB) is the heart of your HVAC system, performing various functions such as relaying thermostat instructions, sensing errors, and displaying error codes. Additionally, it keeps a close eye on input sensors to ensure the safety of your equipment.

When a CCB is defective, it may disregard cooling or heating instructions from the thermostat, potentially causing your thermostat not to blow cold air in the cool mode.

Troubleshooting a Bad Circuit Control Board:

Possible CauseMain Fix
Blown-out fuse on the control boardReplace the 3 or 5 Amp fuse
Defective furnace transformerReplace furnace transformer
Defective transistor or relayReplace control board
Defective control boardReplace control board

Pro Tip: Regularly check your circuit control board for any signs of wear or damage. Timely replacement or repair can prevent disruptions in your HVAC system and ensure efficient operation. 

8) A defective or incompatible thermostat

If you’re using a smart thermostat brand like Honeywell, Google Nest, Ecobee, Sensi, or any other modern thermostat, and it keeps blowing hot air in cool mode, the issue might stem from a defective or incompatible thermostat.

In the era of feature-rich programmable thermostats, it’s easy to be enticed by new models without checking compatibility. Soon, our website will feature a thermostat compatibility checker to assist you in making informed choices before purchasing a thermostat.

If you suspect your thermostat is incompatible with your existing HVAC system, use a compatibility checker or consult a local HVAC professional for guidance. Incompatibility often requires replacing the thermostat. Occasionally, it might be a case of a bad thermostat, which may need cleaning or replacement.

Signs of a Bad Thermostat:

Possible CauseMain Fix
Inconsistent temperaturesClean thermostat, adjust, and if needed, replace
AC or Furnace runs constantlyCheck the wiring
AC or furnace won’t startRecalibrate or properly wire your thermostat
Clean the thermostat, adjust, and if needed, replaceTry changing batteries

Pro Tip: Regularly check for thermostat updates and ensure compatibility with your HVAC system to prevent performance issues. 

9) Leaking freon

Freon plays a crucial role in your air conditioning system’s cooling and heating process. It absorbs heat from indoor air and releases it through the outdoor condenser unit.

When there’s insufficient or no freon in your heat pump or AC, your system won’t be able to produce cool air, even when the thermostat is set to cool mode.

Freon can gradually leak out over time, influenced by system aging or adverse weather conditions.

Detecting a freon leak is challenging, so if you suspect a leak, it’s advisable to consult an HVAC professional. Here are signs indicating a potential freon leak:

  • Air conditioner blowing warm air (not cool)
  • High electricity bills
  • Ice buildup on the refrigerant lines
  • Strange sounds from the condenser unit
  • The set temperature is never reached

A licensed professional will typically identify and seal the leaks upon confirming low freon levels before recharging the system with freon.

Pro Tip: Regular HVAC maintenance, including checking for freon leaks, ensures optimal system performance and energy efficiency.

10) Delay mode

10) Delay mode

The delay mode on any thermostat serves as a brief time off, typically up to 5 minutes, during which the thermostat refrains from activating the heat pump compressor.

This precautionary measure prevents the compressor from starting too quickly, a phenomenon known as short cycling. Short cycling is every day after a power outage or when the system is abruptly turned off and back on.

During the delay period, the compressor remains inactive, while the fan can still blow air. This might explain instances where your thermostat seems to be blowing warm air when set to the cool setting.

It’s essential to note that the delay mode usually lasts no more than 5 minutes. Depending on your thermostat model, you might see a delay message on the display to notify you about this temporary pause.

If 5 minutes pass and the issue persists, another underlying problem might be preventing the cooling in your system. 

Pro Tip: In cases of persistent issues beyond the delay mode, it’s advisable to check for other potential problems or seek assistance from a professional HVAC technician to ensure the efficient operation of your system. 

Answers To Key Questions

Why is my thermostat blowing hot air when I set it to cool?

Your thermostat may have a setting issue. Double-check the cooling settings to ensure they are correctly configured.

Why is my AC blowing hot air in cool setting?

Check your air filter; a dirty filter can restrict airflow, causing the AC to blow warm air. Replace the filter if needed.

Why is my Honeywell thermostat running heat instead of AC?

Verify the mode setting on your thermostat. It might be set to heating instead of cooling. Adjust it accordingly.

Why is my Honeywell thermostat not blowing cold air?

Examine the thermostat’s temperature setting. If set too high, lower it to a cooler temperature to activate the cooling.

Why is my Honeywell thermostat not cooling my house?

Inspect the thermostat’s batteries; low power can affect its function. Replace them if necessary for optimal cooling performance.

Final Thoughts

Now that you’ve discovered the potential reasons behind your Honeywell thermostat blowing hot air on the cool setting, we hope you’ve successfully addressed the issue.

HVAC systems are built to endure for a minimum of 10 years, and with regular annual tune-ups, they can often last even longer.

If, by the end of this guide, you haven’t resolved the cooling problem, it might be prudent to seek the assistance of experts. Professional HVAC technicians can provide the expertise needed to diagnose and fix more complex issues with your system.

Thank you for taking the time to read this article! If you have any additional questions or need more help, please don’t hesitate to ask. I appreciate your engagement! 

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