Heating & Cooling Combined Unit: Why won't my air conditioner turn on?

Check the thermostat settings. Make sure that your air conditioner thermostat is set to Cool and the temperature setting is low enough to call for cooling.

If you have an electronic thermostat and it has no power, check the house circuit breaker for your air conditioning system. Reset the house circuit breaker if it's tripped.

If resetting the house circuit breaker doesn't restore power to the thermostat, then the thermostat may have failed. Replace the thermostat if it's getting power but won't power up. If you replace the thermostat and the air conditioner still won't work, you'll likely need to have a service technician examine and repair the air conditioner.

If the thermostat works and it set properly but the air conditioner won't turn on, the condensate drain float switch may be tripped because the condensate drain line is clogged and water is backed up in the drain system. Clear the clogged drain line so the float switch resets and allows the air conditioner to run.

Other problems that can prevent the air conditioner from running include a wiring failure, bad thermostat and a faulty electronic control board. A service technician typically needs to diagnose and repair these types of air conditioner failures.

heating & cooling combined unit

THESE REPAIRS MAY HELP SOLVE YOUR HEATING & COOLING COMBINED UNIT PROBLEM

Thermostat replacement

Replace the HVAC system thermostat

The thermostat controls the heating and cooling system in your home. The thermostat senses the temperature inside your home and cycles the system on and off to maintain the set temperature. When your HVAC system control thermostat quits working, replace the thermostat.

Hvac system thermostat

Find the required part specific to your product.

HVAC Thermostat
March 3, 2022By Lyle Weischwill

How to replace a heating and air conditioning system thermostat

If the buttons on your HVAC system control thermostat don't work or if the display panel doesn't light up, the thermostat may need to be replaced. This DIY repair guide explains how to replace a thermostat in less than 30 minutes.

Repair difficulty
Time required
 30 minutes or less
Unclog AC drain line

Clear the condensate drain

Your central air conditioner or heat pump has a pipe that drains condensate water that drips from the evaporator to the outside of your home. If the drain pipe or condensate drain system gets clogged, water overflows the drain pan under the evaporator and starts dripping below the inside air conditioner unit. The overflowing condensate can cause water damage in your home.

Many central air conditioners have a drain float switch that shuts the system down if the drain is clogged and water backs up under the evaporator. If this switch trips, the air conditioner will shut down to avoid water damage.

If water drips from below the inside air conditioner unit and/or the air conditioner shuts down because the drain float switch tripped, then it's time to unclog the drain line.

You may be able to remove the clog with a shop vac. If not, you can use a plumber's snake to clear the drain line.

Watch our video Air Conditioner Not Cooling: Float Switches and Drain Pipe Clogs to learn more about fixing and preventing condensate drain system clogs.

To keep the condensate drain system from clogging up in the future, pour a cup of liquid bleach down the drain vent tube every month. The bleach kills mold and mildew that can build up inside the drain pipe and hose. To keep from killing the grass in your yard, stick a pan under the drain hose outside to catch the bleach as it runs out. And always remember to protect your eyes and skin when handling bleach and other harsh chemicals.

Clear the condensate drain

Find the required part specific to your product.

How to unclog the AC drain
March 16, 2022By Sears PartsDirect staff

How to unclog the air conditioner drain line

Follow the steps in this repair guide to unclog condensate drain line for your central air conditioner. Water will drip under the inside AC unit when the drain is clogged.

Repair difficulty
Time required
 15 minutes or less

Symptoms common to all heating & cooling combined units

Choose a symptom to see related heating and air conditioning system repairs.

Dirty air filter, clogged condenser coils, low refrigerant charge, faulty compressor
Thermostat problem, clogged air filter, burner failure
Dirty flame sensor, failed flame sensor, damaged burner, bad high limit switch
Thermostat problems, bad compressor/condenser fan capacitor, lack of refrigerant, failed compressor
Main causes: errant thermostat settings, lack of electrical power, clogged drain line, wiring failure, control failure.
Main causes: Errant thermostat settings, lack of power, bad interlock switches, lack of exhaust ventilation, wiring failures.

Repair guides common to all heating & cooling combined units

These step-by-step repair guides will help you safely fix what’s broken on your HVAC system.

March 16, 2022
By Sears PartsDirect staff
How to unclog the air conditioner drain line

The condensate drain line for your central air conditioner can clog with mold and mildew. Water will back up and start dripping below the inside air conditioner unit. Follow the steps in this guide to unclog the drain pipe.

Repair difficulty
Time required
 15 minutes or less
March 16, 2022
By Sears PartsDirect staff
How to replace the furnace flame sensor

The flame sensor detects when furnace burner flames are lit. You may need to replace the flame sensor if flames only stay on for a few seconds.

Repair difficulty
Time required
 15 minutes or less
How to replace a heating and air conditioning system thermostat

The control thermostat for your HVAC system can stop working. This repair guide shows how to replace it.

Repair difficulty
Time required
 30 minutes or less

Articles and videos common to all heating & cooling combined units

Use the advice and tips in these articles and videos to get the most out of your HVAC system.

August 5, 2022

Introducing new technical repair content that we’re developing for the Sears Technical Institute

By Sears PartsDirect staff

Learn about Sears Technical Institute and the advanced technical content being developed for aspiring appliance techs.

February 22, 2022

Why is my furnace not igniting?

By Lyle Weischwill

Find out why the burner on your furnace isn't igniting.

February 22, 2022

Can a furnace be repaired?

By Lyle Weischwill

Learn about furnace repairs and how much they cost.