What Are AC Coils and Valves and Why Do They Matter?

Bry'Ana Arvie
Written by Bry'Ana Arvie
Updated January 20, 2022
A mother using smartphone while her son is drinking milk
Photo: Portra / E+ / Getty Images


  • Evaporator coils use refrigerant to absorb the heat from your home. 

  • Condenser coils release the heat from the refrigerant outdoors.

  • AC expansion valves regulate how much refrigerant flows through your evaporator.

  • All of these components are important for producing cool air.

  • Maintenance involves changing filters and getting serviced at least once a year.

Get quotes from up to 3 pros!
Enter a zip below and get matched to top-rated pros near you.

When it’s a stifling 90-degree day and the air’s thick enough to touch, thank your AC coils and valves for blasting your AC like the stereos at a Saturday night concert. 

There are countless essential components of your HVAC system, but none are more vital than the coils and valves on a balmy summer day. It’s the evaporator coils, condenser coils, and AC valves that push the actual cool air circulating through your home. Understanding the important role they play in keeping you comfy and the common issues that may arise is key to maintaining your HVAC for longer.

What Is an Evaporator Coil?

Also known as the evaporator core, the evaporator coil absorbs the heat inside your home. This coil—made from aluminum, copper, or steel—sits inside your air handler or blower. An evaporator coil’s job is quick and simple:

  1. The blower pushes warm air over the evaporator coils.

  2. The refrigerant nestled within the coils absorbs the heat and carries it to the condenser coils. 

What Is a Condenser Coil?

After the evaporator coil absorbs your home’s heat, the condenser coils release that heat outside. These copper coils rest inside your outdoor condenser. How a condenser coil works is a bit more complicated:

  1. After the refrigerant absorbs heat from your home’s air, it travels outside via a copper tube to the condenser unit. 

  2. The warm refrigerant gas enters the compressor, where the compressor pressurizes the refrigerant and turns it into a hot gas. 

  3. The condenser coil condenses the pressurized gas into a liquid, releasing the heat the refrigerant absorbed outside. 

  4. The liquid refrigerant travels back inside your home, where the cycle starts again. 

What Does an AC Valve Do?

The AC valve, also known as the expansion valve, controls how much refrigerant flows through your HVAC system. Located in front of the coils, the AC valve acts as a metering device, monitoring when refrigerant can access the coils. (Picture an AC valve as the parent controlling how much candy their kids get. The parent can easily limit candy consumption when present, but kids have unlimited access to those sugary sweets when away, leading to a sugar hype and tummy ache.)

Standard air conditioners use a valve that only opens and closes; however, high-efficiency cooling systems use a thermal expansion valve (TXV). A TXV is like a smart meter, opening and closing in varying degrees so that just enough refrigerant gains access to the coil to meet the cooling load of your home at any given moment. By only allowing the necessary amount of refrigerant in a system at a time, it increases the overall efficiency of your HVAC system. 

Why Are AC Coils and Valves Important?

HVAC heating and air conditioning residential units
Photo: Christian Delbert / Adobe Stock

Your unit's AC coils and valves work in tandem with the compressor to control the cooling output. When operating perfectly, your unit is more efficient. 

The AC valve helps prevent your system from overloading with refrigerant. There are a few consequences for a system that gets too much refrigerant:

  • Your home will fill with lukewarm air

  • Your system will run constantly

  • Your compressor will get damaged

  • Your HVAC system will operate with less efficiency

AC Coils and Valves Maintenance

You can maintain your AC coils and valves are prone to dust, debris, and leaks—all of which affect your unit’s ability to absorb heat, dehumidify your air, and cycle cooler air indoors. Change your AC’s filter monthly to prevent clogs and blockages. Also, contact an HVAC contractor near you to service your unit and clean your AC coils and valves once or twice a year. 

In addition to system maintenance, have your pro inspect your coils for erosion or leaks. If you need to replace these parts, here’s what you should expect to pay:

Need professional help with your project?
Get quotes from top-rated pros.