Blog Post

Common Problems Associated with Oversized DX Air Conditioning Systems

Common Problems Associated with Oversized DX Air Conditioning Systems

Diagnosing what’s wrong with your customer’s air conditioning unit can be a daunting task which can take up a lot of your time and potentially deplete your warranty reserve. One of the most overlooked issues is having too much cooling capacity. If you’re experiencing some of the issues below, we have a solution for you and your customers!

Excessive compressor short cycling

“what causes short cycling to happen?”

Short cycling occurs when an air conditioning unit provides too much cooling capacity for the space and satisfies the thermostat prematurely, effectively shutting the unit off. This excessive compressor cycling creates an unstable and uncomfortable environment in the space, while also placing severe wear and tear on the compressor, reducing the expected lifespan of the equipment.

“how can the apr control help prevent or eliminate short cycling?”

The apr control creates a variable capacity system through mechanical means (refrigeration flow control), reducing the cooling capacity to match the lower load in the space. This will help delay the thermostat from satisfying and allow the unit to stay on. The apr control will provide compressor protection while also creating a more stable indoor environment.

High humidity

“why does humidity build up in an air conditioned space?”

When the setpoint of the space is reached, the thermostat shuts the compressor off. Entering air goes across the inactive (warm) face of the evaporator coil. When this occurs, the latent load (moisture) will not be able to be removed from the air because the evaporator’s temperature is above the dew point of the entering air. To remove moisture from the space, the evaporator coil needs to be active and below the dew point of the return air (or mixed ra/oa). Make sure to look at the runtime of the compressor, it tells a whole lot of the story!

“how can the apr control help manage humidity in an air conditioned space?”

The apr control will extend the runtime of the compressor and maintain the evaporator coil below dewpoint of the entering air by maintaining the suction pressure at around 40 degrees sst. This will allow the dehumidification process to continue, keeping your customers comfortable. While every job is different, rawal devices has helped customers reduce their humidity from 80% rh down to 50% rh in the past! Check out some of our case studies that demonstrate these results.

Varying space temperature

“what causes inconsistent indoor space temperatures?”

When the compressor cycles due to the unit providing too much cooling capacity (again), this can create large swings in discharge air temperature which can cause occupant discomfort. This occurs in both constant volume and vav (variable air volume) systems. The result will be unstable temperatures and will likely lead to the customer calling you with the most common complaint in the hvac industry; “we’re always either too hot or too cold.”

“how can the apr control help stabilize space temperature?”

By reducing the capacity of the air conditioner, the apr control helps avoid the large swings in space temperature by extending the runtime of the unit and creating consistent conditions. If you see major fluctuations in the space temperature and humidity, you should be considering the apr control!

Evaporator freezing & liquid slugging/ compressor floodback

“what causes evaporator freezing and liquid floodback?”

It sounds obvious but overcooling the space will lower the temperature and heat content of the return air. As this lower temperature/lower heat content air goes across the evaporator coil, there are times when there is not enough heat content to evaporate the liquid refrigerant in the evaporator into a gas. If this occurs, it is possible and likely even that straight liquid will go into the compressor and potentially cause a failure. This is referred to as liquid slugging or flood back. Evaporator freezing or frosting takes place when the lack of heat content in the return air allows the evaporator coil to fall below freezing; resulting in the condensation on the coil to ice up, leading to downtime or potential system failure.

“how can the apr control help prevent evaporator freezing and compressor floodback from occurring?”

The apr control offers exceptional compressor protection! The apr control modulates the amount of refrigerant flow sent to the evaporator coil. This will help prevent the evaporator coil from freezing while also sending less refrigerant to make sure the lower heat content of the return air will still be able to evaporator the liquid into the suction gas.

These are just some of the many issues that the apr control can help solve or prevent when dealing with dx air conditioning.
Be sure to sign up for our product overview webinar to learn more and have your questions answered directly.

Learn from Rawal Experts

Get exceptional live technical support for installation and service – call Rawal Devices today!

The Rawal APR Control is a variable capacity enhancement to DX HVAC systems.