Why is My Outside Air Conditioning Unit Not Turning On?

Presidential Heating & Air Conditioning

Gaithersburg HVAC Contractors


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an AC unit that is running thanks to the help of a professional Maryland HVAC contractorSuddenly you notice the air conditioner is not cooling the house. You adjust the thermostat lower and nothing happens. You go outside to see if the outdoor components are working and notice they are not coming on. You immediately think the worst and start having thoughts of all the money it will take to have an HVAC contractor install a new one.

What to Do When Your Outdoor Unit Stops Working

Before you panic, you can try a few DIY troubleshooting steps before calling a professional HVAC contractor for help.

1. Check all power sources. Is the power out anywhere else in the house or in the neighborhood?

Your air conditioner has lots of power sources to check. First, make sure the thermostat setting is on “cool” and is set several degrees below the outdoor temperature.

Outdoor units are powered separately from the indoor unit. Make sure the circuit breaker for the outdoor unit did not trip. Check the circuit breaker and reset it. Flip it to the “off” setting and then back to “on”.

Also, check to see if you have a shutoff box near the AC. You should have an emergency or shut-off switch. It is usually near the outside unit in a metal box on the side of your house. Someone may have switched it to the “off” position and left it off by accident. Sometimes, it can shut off when the condensation drain line becomes too clogged. This will shut down your air conditioner. You can try to unclog the drain line using a wet/dry vacuum to suck out the blockage. If you have a condensate drain pump to pump the condensate to the outdoors, a pump breakdown can trip the emergency switch.

Some also models have a fuse at the shutoff box. You can try replacing this fuse.
Check the power switch for the outdoor condenser or the air handler/furnace. You can often find the switch in your attic, closet, or crawl space near your furnace that can shut off power to your furnace and indoor blower. Sometimes the switch is accidentally flipped to “off”. In the “off” setting, it turns off the blower, causing the inside unit to freeze, which makes your entire air conditioning system shut down.

an outdoor AC unit that needs service repairs from an HVAC contractorMake sure the components are plugged in and all power switches are in the on position. Double check the outlet—if it is a GFI, has the GFI been tripped?

Your system may have a reset button located near the outside unit. Push the button and determine if the power is restored. If your air conditioner does not have a reset button, you can try “rebooting” it by turning off your air conditioner at the thermostat. Wait five minutes, and then turn it back on.

If you have restored the power but the air conditioner switches off again, you will need to call in an HVAC contractor. The system may be pulling too much electricity, short circuiting or overheating, all of which need a professional repair and can be serious problems.

2. Check the AC condensate overflow switch on the air handler. Some air handlers have a small safety float switch connected to the condensation drain pipe. This float switch will turn off the AC if the drainpipe becomes clogged and backs up with water. You should clear the condensation drain pipe or replace it. Over time, these become clogged with algae and dust. Your system may also have an electric condensate pump. If it is old, it should probably be replaced also. Replacing it may be easier than cleaning it out.

3. Check the capacitor and contactor in the compressor. If you hear clicking, humming, or buzzing in the compressor when you turn on the thermostat, you may have a faulty capacitor or contactor. Testing and replacing these parts is a job for an experienced electrician or HVAC technician, as it involves working with significant electrical voltage. However, these components are easy for a professional technician to replace.

If the fan is not working, but the outside unit hums, your problem may be the start capacitor. The capacitor’s job is to give the fan a boost to the fan motor when it starts up. You can test it by gently pushing the fan with a long, skinny stick. If the fan starts to spin then the capacitor needs replacing. If the fan does not start, you may just have a bad fan motor that needs replacing.

4. Check the air filters. They should be changed every three months. If they are old and dirty, the unit can be stressed and may malfunction and freeze up. Replace the filters and leave the system off for a few hours to allow it time to thaw. Use a hose and gently spray dirt off of the compressor. When it is dry, restart the system. If it is operating but not cooling, follow the guidelines below before calling for HVAC service.

a professional HVAC contractor servicing an AC unit5. Contact a professional HVAC technician. If none of these DIY techniques resolved the problem with your AC, it is time to call an expert. You may have a broken compressor, which is usually a major repair. Depending on the age of your system, you may need a system replacement.

Sometimes, homeowners want to replace only the outside condenser/compressor unit rather than the entire system. However, you will often be better off from a performance and efficiency standpoint to avoid trying to patch it together. Your HVAC contractor can provide expert advice on the best way to make this repair in the most cost-effective manner.

Regular Service Will Help Avoid AC Outages

The best way to avoid these midsummer repairs is to have a maintenance agreement in place with a reputable HVAC contractor. You will pay an annual fee for inspection and service on your entire HVAC system at the beginning of the season. They will professionally clean the components, ensure they are operating efficiently, and make minor repairs before problems become major expenses.

Contact a Reputable HVAC Contractor for More Information

Contact a professional HVAC contractor to discuss your air conditioning concerns and schedule an appointment for service.

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