HVAC Condensing Units

Condensing Units caution - Air Conditioning and Heating equipment uses high voltage. Caution is always advised when working around high voltage. When in doubt call a professional. Safety First!!

At least it seems that way to most people. This box made of sheet metal is the heart of your HVAC cooling system. Or for those with heat pumps, it is the heart of your HVAC heating and cooling.

Condensing Units - Heat Pump Condensers

A heat pump condensing unit will look similar to an air conditioning condenser. There are differences in the heat pump condenser and air conditioning condenser equipment. A heat pump condenser has a reversing valve and an air conditioner condenser does not have a reversing valve. A heat pump will provide heating and cooling and an air conditioner will only cool your home or business. Both systems are common in the fact that both types of condensers have condenser coils, a compressor, controls, and a condenser fan motor. Unless you have a water to air or geothermal heat pump system you probably do not have a heat pump if you live North of the Mid-Atlantic region (North of Maryland).

The Heart of Air Conditioner Condensing Units

Scroll Compressor Inside Heat Pump Condenser

The air conditioning & heat pump condensing unit houses the HVAC compressor (the heart of your system). It is the pump that is moving heat to the outside and bringing the refrigerant (which absorbs the heat) to the inside of your home. Vice versa for heat pumps in the winter.

For those of us inside the HVAC heating and cooling business who work on condensing unit compressors, we understand them to be the transferors of heat. This transferor of heat, the compressor (inside the condensing unit), is hermetically sealed and non-serviceable.

It is not much you can do with a burned-up compressor except replace it with a new one. However, there is much you can do to maintain the equipment to give it a longer than average life and keep it running as smoothly and efficiently as the day it was new.

Other components of the air conditioning and heat pump condensing unit include the condenser coils, the condenser fan motor, and several condensing units or heat pump controls.

How a Condensing Unit Works

A heat pump condensing unit is different from an air conditioner condensing unit. They both work using the process of refrigeration to accomplish their goal and they are both similar looking. There are several things going on to make a condenser work outside of this basic description. To learn more about the entire process of a heat pump see our article: How Heat Pumps Work.

And for air conditioners, you will want to visit How Air Conditioners Work. However, for this description, we will cover how a condenser works to show you the details of the condenser. We have covered the components of a condensing unit so you should understand the various parts of the basic condenser.

The vapor refrigerant leaves the evaporator in the suction line. The suction line delivers this heat-saturated vapor to the compressor located in the condensing unit. The compressor compresses this hot vapor increasing the pressure and the temperature of the vapor refrigerant. Once the compressor is done doing its job the now superheated saturated vapor goes into the coils of the condenser.

This process gives the condenser its name. The condensing unit fan motor draws air through the coils and a heat exchange process takes place. As the heat is exchanged from the vapor to the coils to the outside air the refrigerant vapor changes state to a liquid. The vapor condensed to a liquid thereby giving the condensing unit its name. The liquid refrigerant leaves the condenser and goes back through the process again.

Checking the Condensing Units Condenser Fan Motor

In late winter or early Spring, it is a good practice to check the condenser fan motor to make sure it turns. Unplug or turn off the condensing unit at the electrical disconnect box and then set the thermostat to cool. Go back outside and restore power to the condensing unit. Watch the air conditioning units & heat pump condenser fan motor to make sure it turns. The air conditioning & heat pump condenser fan motor should be blowing plenty of air up.

If the HVAC condenser fan motor fails to start it is recommended that it be checked out and replaced if necessary. Whatever the reason there is no need to take chances having the HVAC condenser fan motor fail and cause problems or damage the compressor which will require compressor troubleshooting to determine if the compressor is burned up.

Condenser Fan Motor Failure

If the air conditioning & heat pump condenser fan motor fails on a hot day, the unit stops cooling and the pressures in the condenser rise until a high-pressure switch (not all units are equipped with high-pressure switches) trips or the compressor overload shuts the compressor down. There is a possibility, with a failed HVAC condenser fan motor, that the compressor fails for good never to run again. An HVAC condenser fan motor is a lot cheaper than a compressor. Make sure the condenser fan motor is turning or running before the hot weather arrives.

The Repair

Condenser fan motor repair can be simple and it can be complex and it does involve high voltage so caution is advised. We always advise people to call a professional. The problem can be fixed in a quick efficient manner and any related problems that could have caused the issue can be rectified.

Safely. In some cases, the fan motor is not bad. It could be another electrical component in the system causing the problem such as the AC or heat pump run capacitor for the motor. It could also be the air conditioner compressor contactor causing the problem. Either way, a professional HVAC technician can fix the problem quickly and efficiently.

Some condensing units have ECM condenser fan motors. The condensers typically are staged or modulating condensing units for high-efficiency systems. They are typically controlled by an electronic circuit board or other solid-state control and usually require a special diagnostic tool to troubleshoot.

Basic Condenser Maintenance & Upkeep

The question you are probably asking now is “What can I do to keep the condensing unit running smoothly and efficiently?” First, you can keep the air conditioning & heat pump condenser coils clean of grass, dirt, and mud. Over time, these things build up inside the HVAC condenser coils and block the condenser coils. This accumulation of debris reduces the designed surface area of the air conditioning & heat pump condenser coils.

Reducing that surface area of the condenser causes the compressor to work harder because there is less heat being exchanged from the HVAC condensing unit coils to the atmosphere. The less heat being displaced to the outside air the more heat stays inside the condensing unit and the refrigerant. This causes the condensing unit pressures to rise inside the condensing unit.

Condensing Units - Keeping the Condenser Efficient

For the typical*air conditioner (AC) or heat pump, the pressures should not exceed 300 P.S.I.G. on the hottest day of the year. *(Recent HFC refrigerants out on the market operate at higher design pressures.) If your condensing unit has dirty condensing coils and the thermometer outside is above 70 degrees then your condensing unit is most likely running at a higher pressure than it is designed to run at. The solution is to clean the HVAC condensing unit coils.

Cleaning the Air Conditioning & Heat Pump Condensing Unit Coils

Clean Coils are important

Before you drag the water hose over to the condensing unit and start spraying, you’ll want to secure the condensing unit. This begins at the HVAC thermostat and ends at the condenser electrical disconnect box located at the condensing unit.

Turn the thermostat to the off position and pull the plug inside the condenser electrical disconnect box. Some condenser electrical disconnects have a switch like a circuit breaker located inside them. Turn the power off.

Condensing Units Cleaning

After the power is off and the air conditioning & heat pump condensing unit is secure, break out the water hose with a good nozzle that will allow you to spray water at high pressure.

A little soap will help clean the dirt and other debris off the HVAC condenser coils also. Apply the soap and let it soak for a few minutes. Then spray the condenser coils. Be careful not to use too much pressure as you may bend some of the heat exchange fins that surround the air conditioning & heat pump condenser coils.

Condensing Units - Inside Out

For best results, it will help if you spray the water from the inside of the condensing unit coils out. This may require you to take the top of the condensing unit off. If you are not mechanically inclined do not attempt this procedure. Simply spray all the dirt and debris off the HVAC condensing unit coils as you can possibly spray off.

Electrical Connections

When doing maintenance one of the things the tech does is check the electrical connections. A loose electrical connection can cause problems including failure of the system. Of course, as previously mentioned, a condensing unit has high voltage inside so we never advise you to open the cabinet unless you are specifically trained in working around high voltage.

Even with the power off, there is a potential for electric shock inside the condenser. Along with low voltage controls, there are two main high voltage components in the typical condensing unit. The compressor and the condenser fan motor with the compressor pulling more current than the fan. It is important to check the electrical connections from time to time to prevent problems including failure.

Advised Caution

Among the things to be aware of around the air conditioning & heat pump condensing unit are:

• Weed Eaters around the electrical wires especially the thermostat wire.
• branches from trees falling into the fan blade.
• Insects getting inside the condensing unit and inside critical electrical components.
• Children playing around the condensing unit (toys like balls can bend the heat exchange fins on the condensing unit reducing airflow).
• plastic children’s pools, tarps, and other objects which can be picked up by the wind and blown on top of the condensing unit. There should not be any objects blocking airflow over the condensing unit and at least 2 feet of space around the sides of the condensing unit.

Condensing Units Additional Resource

In some cases, when a catastrophic failure occurs in the condenser, you can elect to have just the condensing unit replaced rather than the entire system. It is important that the indoor system is matched with the new condenser and the HVAC contractor should be able to accommodate you and take care of all the technical specifics in this case. Whether it is a heat pump condenser or an air conditioner condenser you can simply replace the condensing unit and leave the indoor air handler in place. To see some reviews of condenser visit or condensing unit reviews pages: Condensing Unit Reviews for Various Brands

Condensing Units

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