New Honeywell Thermostat Blowing Hot Air on Cool [Solved]

Is your new Honeywell thermostat blowing hot air on cool mode? It can be frustrating to wake up in the middle of the night sweating only to discover that your newly installed Honeywell thermostat is not cooling.

There could be a few reasons your Honeywell thermostat is blowing warm instead of cool air, especially if it’s a new installation. These include:

  • Your outdoor ac unit has no power access (tripped circuit breakers)
  • Wrong thermostat wiring
  • Your system is in delay mode
  • Compatibility issues
  • Changeover valve issues

Read also: Honeywell Thermostat Not Cooling [8 Easy Solutions]

Reasons A New Honeywell Thermostat Would Blow Hot Air on Cool Mode

It’s not uncommon for a new thermostat to misbehave after an installation. This is mainly because of errors made during the installation, system compatibility issues, and just a few other reasons. Let’s now go straight into details.

1) System Is in Delay Mode

If you have set your Honeywell thermostat to cool mode and its flashing ‘cool on’ but blowing warm air instead of cold, your thermostat could be in delay mode. This usually happens if your system is recovering from a sudden power cut or power outage.

The thermostat has a delay mode functionality that protects your compressor and your entire equipment from short cycling. However, delay mode should not take more than 5 minutes.  If the delay mode is not an issue, let’s jump right into the second step of our troubleshooting.

2) You Are Using a Conventional System

When you are dealing with a Honeywell thermostat that is blowing hot air on cool mode, you first want to verify that you have a heat pump and not a conventional system. A heat pump should blow cool air on cool mode, but a furnace will not.

To know if you have a heat pump, try setting your thermostat to heat mode and raise the temperature to a point above the current room temperature reading. If the outdoor unit (condenser kicks on), you’ll know it’s a heat pump.

But this method can not work if there is a power cut to your outdoor unit. In this case, the best you can do to tell if you have a heat pump is to head over to your outdoor unit and check the label on it.

If there is anything labeled ‘heat pump,’ you’ll know your system is a heat pump. If there is no ‘heat pump’ label, you can copy the model number from the label and look it up on the internet. The result should display information about the kind of system you have (heat pump or not.)

3) Your Outdoor Unit Has No Power Access

When troubleshooting a thermostat that’s not cooling, verifying that your outdoor condenser unit has access to power is essential.  After installing your new thermostat, you might have forgotten to turn on the circuit breaker for your ac condenser unit.

If your condenser unit can’t turn on because of power issues, it won’t be able to dispose of the heat from your home. And that could be the reason your thermostat is blowing warm air instead of cool air.

Check once more that the breakers are up and conducting power to your condenser unit. Sometimes, you might have blown out fuses in your disconnect (outdoor device installed on your house wall). And other times, blown fuses on the control board could be why your system is not blowing cold.

Check your thermostat orientation to see if your condenser unit is running correctly but your thermostat is blowing hot air on cool mode.

Also read: Honeywell Thermostat Heat Not Working [7 Fixes]

4) Bad Thermostat Wiring

If your thermostat is blowing hot on cool mode, thermostat wiring issues could occur. You must ensure that the wiring from the old thermostat is correctly matched to the new thermostat. On top of that, both terminals R (for power) and Ric  (power for cooling) have to be connected. If these two terminals are not connected by separate wires, use a jumper (a short wire) to connect the two.

To make a jumper, you can just cut and strip off a small piece of wire from one of those wires.

How should I wire my Honeywell thermostat?

Each terminal has a specific function. For example, wires that control cooling are different from those that control your system’s heating. These wires must be appropriately connected if your thermostat is to work without issues.

The O/B is responsible for controlling the changeover valve. Ensure it’s connected and there are no loose wires in your thermostat installation. Before touching your thermostat wires, verify that you have turned off power to your system in the circuit breaker. This is for your safety and also that of your equipment. Take a look at the wiring diagram for your Honeywell thermostat below:

S – Indoor and Outdoor Wired Sensors

Y – Compressor Stage 1 (Cooling)

Y2 – Compressor Stage 2 (Cooling)

G – Fan

C – Common

U – Humidifier, Dehumidifier, or Ventilator control

L/A – A – Input for heat pump fault

O/B – Reversing valve for Heat Pump systems

E – Emergency Heat

Aux / W2 – Heat Stage 2 (Heating)

W – Heat Stage 1 (Heating)

R – 24vac (Heating transformer)

Arc – 24vac (Cooling transformer)

5) Changeover Valve Issues

A defective changeover valve can be why your Honeywell thermostat is not cooling your home. A change-over valve is a device on your heat pump that reverses the flow of the refrigerant. Because of that, your heat pump can work as a heater and an air conditioner in the cooling.

However, if the changeover valve gets stuck in the heating position, your thermostat won’t do enough to help resolve this problem. Fortunately, changeover valves are replaceable. A defective changeover valve can be replaced, and cooling for your home can be restored in no time. You’ll need to call professionals to come and replace it for you.

Also read: Honeywell Thermostat Won’t Turn on AC [Solved]

6) Thermostat Compatibility Issues

Your thermostat is not cooling your home probably because it’s incompatible with your existing system. It’s very tempting to buy a very nice smart thermostat without checking the compatibility with your system. Some newer thermostats are not compatible with older HVAC systems. If you are unsure whether or not your thermostat is compatible with your system, call HVAC professionals for advice.

Or shop for new Honeywell Thermostats below:

SaleBestseller No. 1
Honeywell Home RTH9585WF Wi-Fi Smart Color Thermostat, 7 Day Programmable, Touch Screen, Energy Star, Alexa Ready, C-Wire Required, Not Compatible with Line Volt Heating Gray
  • COMFORT COMES IN YOUR COLOR. Personalize your Wi-Fi Smart Color Programmable Thermostat to fit your décor.
  • SAVE ENERGY AND GET REWARDED by checking with your energy provider about available rebates. Plus, eligible customers can enroll in their local Utility’s “DEMAND RESPONSE PROGRAM” which can reward you for allowing the utility to slightly adjust your AC or furnace temperature settings when there is high energy demand.
  • YOUR SCHEDULE. YOUR WAY. Flexible programming options for your schedule or utility company’s peak rate pricing.
  • EASY OPERATION AND INTUITIVE. Bright, easy-to-read touchscreen makes for simple operation.
  • COMPATIBLE WITH: Forced air (gas, oil or electric), hot water and steam, and heat pumps with electric backup. Does NOT work with electric baseboard heat (120-240V). C-Wire required.
SaleBestseller No. 2
Honeywell TH4110U2005/U T4 Pro Program Mable Thermostat, White
  • Country Of Origin: United States
  • Model Number: TH4110U2005/U
  • Item Package Dimension: 6.49999999337″ L x 5.099999994798″ W x 2.299999997654″ H
  • Item Package Weight: 13.8 oz
SaleBestseller No. 3
Honeywell Home RTH2300B 5-2 Day Programmable Thermostat
  • 5-2 DAY PROGRAMMING: Separate programs for the weekdays and weekends with 4 program periods per day including wake, leave, arrive and sleep
  • PRECISE TEMPERATURE CONTROL: Precise temperature control of plus/- 1 degree Fahrenheit. Temperature range limits allow you to set minimum cooling and maximum heating temperatures
  • DIGITAL DISPLAY: The display panel is backlit with an intuitive interface for one-touch access to setpoint temperature
  • EASY INSTALLATION: Easy to install yourself and works with many heating/cooling systems, plus heat pumps without auxiliary heat
  • REMINDERS: Built-in battery change and filter change reminders

7) Malfunctioning Control Board

control board compartment
Control board compartment

If your furnace control board is malfunctioning, it could prevent your system from responding to temperature adjustments from your thermostat.

The control board receives instructions about cooling and heating from your thermostat. Then relays this information to every other component of your system concerned with that specific instruction.

Sometimes the control board can become irresponsive to the thermostat, and all it needs to start working again is a reset. You can reset your furnace’s control board by turning off your furnace by either the power switch or the circuit breaker for about 5-to 10 minutes and restarting.

An utterly dead furnace control board is replaceable. But for this fix, you’ll need the help of professionals.


Why Is There a Jumper Between R And RC in a Honeywell Thermostat?

The R terminal is for power (for the entire HVAC system), and the R c is power for cooling. These two terminals need to be connected separately to the furnace control board. A jumper will be needed to connect both terminals if only one is connected. If the Rc terminal is not connected, your thermostat won’t be able to cool.

How Many Wires Are on A Heat Pump?

Depending on the type of heat pump, the number of connecting wires can vary from 5 to 8, with 2nd-stage heat pumps having more wires than single-stage heat pumps.

What Color Is the C Wire?

The C-wires are typically blue in color. C-wires are necessary in most modern thermostats, they supply them with a continuous 24volts power supply.

Final Thought

We hope that this troubleshooting guide about your new Honeywell thermostat blowing hot air on cool mode has been helpful. Otherwise, if the problem continues after trying out the tips given in this article, then it’s best you call local professional HVAC guys.

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